Pass struct kvm_page_fault to handle_abnormal_pfn() instead of
extracting the arguments from the struct.
Suggested-by: Isaku Yamahata <isaku.yamahata@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Add fields to struct kvm_page_fault corresponding to outputs of
kvm_faultin_pfn(). For now they have to be extracted again from struct
kvm_page_fault in the subsequent steps, but this is temporary until
other functions in the chain are switched over as well.
Suggested-by: Isaku Yamahata <isaku.yamahata@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Add fields to struct kvm_page_fault corresponding to the arguments
of page_fault_handle_page_track(). The fields are initialized in the
callers, and page_fault_handle_page_track() receives a struct
kvm_page_fault instead of having to extract the arguments out of it.
Suggested-by: Isaku Yamahata <isaku.yamahata@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Add fields to struct kvm_page_fault corresponding to
the arguments of direct_page_fault(). The fields are
initialized in the callers, and direct_page_fault()
receives a struct kvm_page_fault instead of having to
extract the arguments out of it.
Also adjust FNAME(page_fault) to store the max_level in
struct kvm_page_fault, to keep it similar to the direct
map path.
Suggested-by: Isaku Yamahata <isaku.yamahata@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Pass struct kvm_page_fault to mmu->page_fault() instead of
extracting the arguments from the struct. FNAME(page_fault) can use
the precomputed bools from the error code.
Suggested-by: Isaku Yamahata <isaku.yamahata@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Do not bother removing the low bits of the gpa. This masking dates back
to the very first commit of KVM but it is unnecessary, as exemplified
by the other call in kvm_tdp_page_fault.
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
So far, the loop bodies already ensure the PTE is present before calling
__shadow_walk_next(): Some loop bodies simply exit with a !PRESENT
directly and some other loop bodies, i.e. FNAME(fetch) and __direct_map()
do not currently guard their walks with is_shadow_present_pte, but only
because they install present non-leaf SPTEs in the loop itself.
But checking pte present in __shadow_walk_next() (which is called from
shadow_walk_okay()) is more prudent; walking past a !PRESENT SPTE
would lead to attempting to read a the next level SPTE from a garbage
iter->shadow_addr. It also allows to remove the is_shadow_present_pte()
checks from the loop bodies.
Reviewed-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Lai Jiangshan <laijs@linux.alibaba.com>
Message-Id: <20210906122547.263316-2-jiangshanlai@gmail.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
If the original spte is writable, the target gfn should not be the
gfn of synchronized shadowpage and can continue to be writable.
When !can_unsync, speculative must be false. So when the check of
"!can_unsync" is removed, we need to move the label of "out" up.
Signed-off-by: Lai Jiangshan <laijs@linux.alibaba.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Message-Id: <20210918005636.3675-11-jiangshanlai@gmail.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
We'd better only unsync the pagetable when there just was a really
write fault on a level-1 pagetable.
Signed-off-by: Lai Jiangshan <laijs@linux.alibaba.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Message-Id: <20210918005636.3675-10-jiangshanlai@gmail.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Its solo caller is changed to use FNAME(prefetch_gpte) directly.
Signed-off-by: Lai Jiangshan <laijs@linux.alibaba.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Message-Id: <20210918005636.3675-9-jiangshanlai@gmail.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
In mmu_sync_children(), it can zap the invalid list after remote tlb flushing.
Emptifying the invalid list ASAP might help reduce a remote tlb flushing
in some cases.
Signed-off-by: Lai Jiangshan <laijs@linux.alibaba.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Message-Id: <20210918005636.3675-8-jiangshanlai@gmail.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Currently kvm_sync_page() returns true when there is any present spte.
But the return value is ignored in the callers.
Changing kvm_sync_page() to return true when remote flush is needed and
changing mmu->sync_page() not to directly flush can combine and reduce
remote flush requests.
Signed-off-by: Lai Jiangshan <laijs@linux.alibaba.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Message-Id: <20210918005636.3675-7-jiangshanlai@gmail.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Because local_flush is useless, kvm_mmu_flush_or_zap() can be removed
and kvm_mmu_remote_flush_or_zap is used instead.
Signed-off-by: Lai Jiangshan <laijs@linux.alibaba.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Message-Id: <20210918005636.3675-6-jiangshanlai@gmail.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
After any shadow page modification, flushing tlb only on current VCPU
is weird due to other VCPU's tlb might still be stale.
In other words, if there is any mandatory tlb-flushing after shadow page
modification, SET_SPTE_NEED_REMOTE_TLB_FLUSH or remote_flush should be
set and the tlbs of all VCPUs should be flushed. There is not point to
only flush current tlb except when the request is from vCPU's or pCPU's
activities.
If there was any bug that mandatory tlb-flushing is required and
SET_SPTE_NEED_REMOTE_TLB_FLUSH/remote_flush is failed to set, this patch
would expose the bug in a more destructive way. The related code paths
are checked and no missing SET_SPTE_NEED_REMOTE_TLB_FLUSH is found yet.
Currently, there is no optional tlb-flushing after sync page related code
is changed to flush tlb timely. So we can just remove these local flushing
code.
Signed-off-by: Lai Jiangshan <laijs@linux.alibaba.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Message-Id: <20210918005636.3675-5-jiangshanlai@gmail.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Make a final call to direct_pte_prefetch_many() if there are "trailing"
SPTEs to prefetch, i.e. SPTEs for GFNs following the faulting GFN. The
call to direct_pte_prefetch_many() in the loop only handles the case
where there are !PRESENT SPTEs preceding a PRESENT SPTE.
E.g. if the faulting GFN is a multiple of 8 (the prefetch size) and all
SPTEs for the following GFNs are !PRESENT, the loop will terminate with
"start = sptep+1" and not prefetch any SPTEs.
Prefetching trailing SPTEs as intended can drastically reduce the number
of guest page faults, e.g. accessing the first byte of every 4kb page in
a 6gb chunk of virtual memory, in a VM with 8gb of preallocated memory,
the number of pf_fixed events observed in L0 drops from ~1.75M to <0.27M.
Note, this only affects memory that is backed by 4kb pages as KVM doesn't
prefetch when installing hugepages. Shadow paging prefetching is not
affected as it does not batch the prefetches due to the need to process
the corresponding guest PTE. The TDP MMU is not affected because it
doesn't have prefetching, yet...
Fixes: 957ed9effd ("KVM: MMU: prefetch ptes when intercepted guest #PF")
Cc: Sergey Senozhatsky <senozhatsky@google.com>
Cc: Ben Gardon <bgardon@google.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20210818235615.2047588-1-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
If gpte is changed from non-present to present, the guest doesn't need
to flush tlb per SDM. So the host must synchronze sp before
link it. Otherwise the guest might use a wrong mapping.
For example: the guest first changes a level-1 pagetable, and then
links its parent to a new place where the original gpte is non-present.
Finally the guest can access the remapped area without flushing
the tlb. The guest's behavior should be allowed per SDM, but the host
kvm mmu makes it wrong.
Fixes: 4731d4c7a0 ("KVM: MMU: out of sync shadow core")
Signed-off-by: Lai Jiangshan <laijs@linux.alibaba.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Message-Id: <20210918005636.3675-3-jiangshanlai@gmail.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
When kvm->tlbs_dirty > 0, some rmaps might have been deleted
without flushing tlb remotely after kvm_sync_page(). If @gfn
was writable before and it's rmaps was deleted in kvm_sync_page(),
and if the tlb entry is still in a remote running VCPU, the @gfn
is not safely protected.
To fix the problem, kvm_sync_page() does the remote flush when
needed to avoid the problem.
Fixes: a4ee1ca4a3 ("KVM: MMU: delay flush all tlbs on sync_page path")
Signed-off-by: Lai Jiangshan <laijs@linux.alibaba.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Message-Id: <20210918005636.3675-2-jiangshanlai@gmail.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Check the return of init_srcu_struct(), which can fail due to OOM, when
initializing the page track mechanism. Lack of checking leads to a NULL
pointer deref found by a modified syzkaller.
Reported-by: TCS Robot <tcs_robot@tencent.com>
Signed-off-by: Haimin Zhang <tcs_kernel@tencent.com>
Message-Id: <1630636626-12262-1-git-send-email-tcs_kernel@tencent.com>
[Move the call towards the beginning of kvm_arch_init_vm. - Paolo]
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
It is reasonable for these functions to be used only in some configurations,
for example only if the host is 64-bits (and therefore supports 64-bit
guests). It is also reasonable to keep the role_regs and role accessors
in sync even though some of the accessors may be used only for one of the
two sets (as is the case currently for CR4.LA57)..
Because clang reports warnings for unused inlines declared in a .c file,
mark both sets of accessors as __maybe_unused.
Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Move "lpage_disallowed_link" out of the first 64 bytes, i.e. out of the
first cache line, of kvm_mmu_page so that "spt" and to a lesser extent
"gfns" land in the first cache line. "lpage_disallowed_link" is accessed
relatively infrequently compared to "spt", which is accessed any time KVM
is walking and/or manipulating the shadow page tables.
No functional change intended.
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20210901221023.1303578-4-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Move "tdp_mmu_page" into the 1-byte void left by the recently removed
"mmio_cached" so that it resides in the first 64 bytes of kvm_mmu_page,
i.e. in the same cache line as the most commonly accessed fields.
Don't bother wrapping tdp_mmu_page in CONFIG_X86_64, including the field in
32-bit builds doesn't affect the size of kvm_mmu_page, and a future patch
can always wrap the field in the unlikely event KVM gains a 1-byte flag
that is 32-bit specific.
Note, the size of kvm_mmu_page is also unchanged on CONFIG_X86_64=y due
to it previously sharing an 8-byte chunk with write_flooding_count.
No functional change intended.
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20210901221023.1303578-3-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Revert a misguided illegal GPA check when "translating" a non-nested GPA.
The check is woefully incomplete as it does not fill in @exception as
expected by all callers, which leads to KVM attempting to inject a bogus
exception, potentially exposing kernel stack information in the process.
WARNING: CPU: 0 PID: 8469 at arch/x86/kvm/x86.c:525 exception_type+0x98/0xb0 arch/x86/kvm/x86.c:525
CPU: 1 PID: 8469 Comm: syz-executor531 Not tainted 5.14.0-rc7-syzkaller #0
RIP: 0010:exception_type+0x98/0xb0 arch/x86/kvm/x86.c:525
Call Trace:
x86_emulate_instruction+0xef6/0x1460 arch/x86/kvm/x86.c:7853
kvm_mmu_page_fault+0x2f0/0x1810 arch/x86/kvm/mmu/mmu.c:5199
handle_ept_misconfig+0xdf/0x3e0 arch/x86/kvm/vmx/vmx.c:5336
__vmx_handle_exit arch/x86/kvm/vmx/vmx.c:6021 [inline]
vmx_handle_exit+0x336/0x1800 arch/x86/kvm/vmx/vmx.c:6038
vcpu_enter_guest+0x2a1c/0x4430 arch/x86/kvm/x86.c:9712
vcpu_run arch/x86/kvm/x86.c:9779 [inline]
kvm_arch_vcpu_ioctl_run+0x47d/0x1b20 arch/x86/kvm/x86.c:10010
kvm_vcpu_ioctl+0x49e/0xe50 arch/x86/kvm/../../../virt/kvm/kvm_main.c:3652
The bug has escaped notice because practically speaking the GPA check is
useless. The GPA check in question only comes into play when KVM is
walking guest page tables (or "translating" CR3), and KVM already handles
illegal GPA checks by setting reserved bits in rsvd_bits_mask for each
PxE, or in the case of CR3 for loading PTDPTRs, manually checks for an
illegal CR3. This particular failure doesn't hit the existing reserved
bits checks because syzbot sets guest.MAXPHYADDR=1, and IA32 architecture
simply doesn't allow for such an absurd MAXPHYADDR, e.g. 32-bit paging
doesn't define any reserved PA bits checks, which KVM emulates by only
incorporating the reserved PA bits into the "high" bits, i.e. bits 63:32.
Simply remove the bogus check. There is zero meaningful value and no
architectural justification for supporting guest.MAXPHYADDR < 32, and
properly filling the exception would introduce non-trivial complexity.
This reverts commit ec7771ab47.
Fixes: ec7771ab47 ("KVM: x86: mmu: Add guest physical address check in translate_gpa()")
Cc: stable@vger.kernel.org
Reported-by: syzbot+200c08e88ae818f849ce@syzkaller.appspotmail.com
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20210831164224.1119728-2-seanjc@google.com>
Reviewed-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
After reverting and restoring the fast tlb invalidation patch series,
the mmio_cached is not removed. Hence a unused field is left in
kvm_mmu_page.
Cc: Sean Christopherson <seanjc@google.com>
Signed-off-by: Jia He <justin.he@arm.com>
Message-Id: <20210830145336.27183-1-justin.he@arm.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Include pml5_root in the set of special roots if and only if the host,
and thus NPT, is using 5-level paging. mmu_alloc_special_roots() expects
special roots to be allocated as a bundle, i.e. they're either all valid
or all NULL. But for pml5_root, that expectation only holds true if the
host uses 5-level paging, which causes KVM to WARN about pml5_root being
NULL when the other special roots are valid.
The silver lining of 4-level vs. 5-level NPT being tied to the host
kernel's paging level is that KVM's shadow root level is constant; unlike
VMX's EPT, KVM can't choose 4-level NPT based on guest.MAXPHYADDR. That
means KVM can still expect pml5_root to be bundled with the other special
roots, it just needs to be conditioned on the shadow root level.
Fixes: cb0f722aff ("KVM: x86/mmu: Support shadowing NPT when 5-level paging is enabled in host")
Reported-by: Maxim Levitsky <mlevitsk@redhat.com>
Reviewed-by: Maxim Levitsky <mlevitsk@redhat.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20210824005824.205536-1-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
When the 5-level page table CPU flag is set in the host, but the guest
has CR4.LA57=0 (including the case of a 32-bit guest), the top level of
the shadow NPT page tables will be fixed, consisting of one pointer to
a lower-level table and 511 non-present entries. Extend the existing
code that creates the fixed PML4 or PDP table, to provide a fixed PML5
table if needed.
This is not needed on EPT because the number of layers in the tables
is specified in the EPTP instead of depending on the host CR4.
Suggested-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Wei Huang <wei.huang2@amd.com>
Message-Id: <20210818165549.3771014-3-wei.huang2@amd.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
AMD future CPUs will require a 5-level NPT if host CR4.LA57 is set.
To prevent kvm_mmu_get_tdp_level() from incorrectly changing NPT level
on behalf of CPUs, add a new parameter in kvm_configure_mmu() to force
a fixed TDP level.
Signed-off-by: Wei Huang <wei.huang2@amd.com>
Message-Id: <20210818165549.3771014-2-wei.huang2@amd.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This change started as a way to make kvm_mmu_hugepage_adjust a bit simpler,
but it does fix two bugs as well.
One bug is in zapping collapsible PTEs. If a large page size is
disallowed but not all of them, kvm_mmu_max_mapping_level will return the
host mapping level and the small PTEs will be zapped up to that level.
However, if e.g. 1GB are prohibited, we can still zap 4KB mapping and
preserve the 2MB ones. This can happen for example when NX huge pages
are in use.
The second would happen when userspace backs guest memory
with a 1gb hugepage but only assign a subset of the page to
the guest. 1gb pages would be disallowed by the memslot, but
not 2mb. kvm_mmu_max_mapping_level() would fall through to the
host_pfn_mapping_level() logic, see the 1gb hugepage, and map the whole
thing into the guest.
Fixes: 2f57b7051f ("KVM: x86/mmu: Persist gfn_lpage_is_disallowed() to max_level")
Cc: stable@vger.kernel.org
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Drop @shared from tdp_mmu_link_page() and hardcode it to work for
mmu_lock being held for read. The helper has exactly one caller and
in all likelihood will only ever have exactly one caller. Even if KVM
adds a path to install translations without an initiating page fault,
odds are very, very good that the path will just be a wrapper to the
"page fault" handler (both SNP and TDX RFCs propose patches to do
exactly that).
No functional change intended.
Cc: Ben Gardon <bgardon@google.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20210810224554.2978735-3-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Existing KVM code tracks the number of large pages regardless of their
sizes. Therefore, when large page of 1GB (or larger) is adopted, the
information becomes less useful because lpages counts a mix of 1G and 2M
pages.
So remove the lpages since it is easy for user space to aggregate the info.
Instead, provide a comprehensive page stats of all sizes from 4K to 512G.
Suggested-by: Ben Gardon <bgardon@google.com>
Reviewed-by: David Matlack <dmatlack@google.com>
Reviewed-by: Ben Gardon <bgardon@google.com>
Signed-off-by: Mingwei Zhang <mizhang@google.com>
Cc: Jing Zhang <jingzhangos@google.com>
Cc: David Matlack <dmatlack@google.com>
Cc: Sean Christopherson <seanjc@google.com>
Message-Id: <20210803044607.599629-4-mizhang@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Factor in whether or not the old/new SPTEs are shadow-present when
adjusting the large page stats in the TDP MMU. A modified MMIO SPTE can
toggle the page size bit, as bit 7 is used to store the MMIO generation,
i.e. is_large_pte() can get a false positive when called on a MMIO SPTE.
Ditto for nuking SPTEs with REMOVED_SPTE, which sets bit 7 in its magic
value.
Opportunistically move the logic below the check to verify at least one
of the old/new SPTEs is shadow present.
Use is/was_leaf even though is/was_present would suffice. The code
generation is roughly equivalent since all flags need to be computed
prior to the code in question, and using the *_leaf flags will minimize
the diff in a future enhancement to account all pages, i.e. will change
the check to "is_leaf != was_leaf".
Reviewed-by: David Matlack <dmatlack@google.com>
Reviewed-by: Ben Gardon <bgardon@google.com>
Fixes: 1699f65c8b ("kvm/x86: Fix 'lpages' kvm stat for TDM MMU")
Cc: stable@vger.kernel.org
Signed-off-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Mingwei Zhang <mizhang@google.com>
Message-Id: <20210803044607.599629-3-mizhang@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Drop an unnecessary is_shadow_present_pte() check when updating the rmaps
after installing a non-MMIO SPTE. set_spte() is used only to create
shadow-present SPTEs, e.g. MMIO SPTEs are handled early on, mmu_set_spte()
runs with mmu_lock held for write, i.e. the SPTE can't be zapped between
writing the SPTE and updating the rmaps.
Opportunistically combine the "new SPTE" logic for large pages and rmaps.
No functional change intended.
Suggested-by: Ben Gardon <bgardon@google.com>
Reviewed-by: David Matlack <dmatlack@google.com>
Reviewed-by: Ben Gardon <bgardon@google.com>
Reviewed-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Mingwei Zhang <mizhang@google.com>
Message-Id: <20210803044607.599629-2-mizhang@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
on AMD, APIC virtualization needs to dynamicaly inhibit the AVIC in a
response to some events, and this is problematic and not efficient to do by
enabling/disabling the memslot that covers APIC's mmio range.
Plus due to SRCU locking, it makes it more complex to
request AVIC inhibition.
Instead, the APIC memslot will be always enabled, but be invisible
to the guest, such as the MMU code will not install a SPTE for it,
when it is inhibited and instead jump straight to emulating the access.
When inhibiting the AVIC, this SPTE will be zapped.
This code is based on a suggestion from Sean Christopherson:
https://lkml.org/lkml/2021/7/19/2970
Suggested-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Maxim Levitsky <mlevitsk@redhat.com>
Message-Id: <20210810205251.424103-8-mlevitsk@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This will allow it to return RET_PF_EMULATE for APIC mmio
emulation.
This code is based on a patch from Sean Christopherson:
https://lkml.org/lkml/2021/7/19/2970
Suggested-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Maxim Levitsky <mlevitsk@redhat.com>
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Message-Id: <20210810205251.424103-7-mlevitsk@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
try_async_pf is a wrong name for this function, since this code
is used when asynchronous page fault is not enabled as well.
This code is based on a patch from Sean Christopherson:
https://lkml.org/lkml/2021/7/19/2970
Suggested-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Maxim Levitsky <mlevitsk@redhat.com>
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Message-Id: <20210810205251.424103-6-mlevitsk@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This together with previous patch, ensures that
kvm_zap_gfn_range doesn't race with page fault
running on another vcpu, and will make this page fault code
retry instead.
This is based on a patch suggested by Sean Christopherson:
https://lkml.org/lkml/2021/7/22/1025
Suggested-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Maxim Levitsky <mlevitsk@redhat.com>
Message-Id: <20210810205251.424103-5-mlevitsk@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This comment makes it clear that the range of gfns that this
function receives is non inclusive.
Signed-off-by: Maxim Levitsky <mlevitsk@redhat.com>
Message-Id: <20210810205251.424103-4-mlevitsk@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
kvm_flush_remote_tlbs_with_address expects (start gfn, number of pages),
and not (start gfn, end gfn)
Signed-off-by: Maxim Levitsky <mlevitsk@redhat.com>
Message-Id: <20210810205251.424103-3-mlevitsk@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This together with the next patch will fix a future race between
kvm_zap_gfn_range and the page fault handler, which will happen
when AVIC memslot is going to be only partially disabled.
The performance impact is minimal since kvm_zap_gfn_range is only
called by users, update_mtrr() and kvm_post_set_cr0().
Both only use it if the guest has non-coherent DMA, in order to
honor the guest's UC memtype.
MTRR and CD setup only happens at boot, and generally in an area
where the page tables should be small (for CD) or should not
include the affected GFNs at all (for MTRRs).
This is based on a patch suggested by Sean Christopherson:
https://lkml.org/lkml/2021/7/22/1025
Signed-off-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Maxim Levitsky <mlevitsk@redhat.com>
Message-Id: <20210810205251.424103-2-mlevitsk@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Use this file to dump rmap statistic information. The statistic is done by
calculating the rmap count and the result is log-2-based.
An example output of this looks like (idle 6GB guest, right after boot linux):
Rmap_Count: 0 1 2-3 4-7 8-15 16-31 32-63 64-127 128-255 256-511 512-1023
Level=4K: 3086676 53045 12330 1272 502 121 76 2 0 0 0
Level=2M: 5947 231 0 0 0 0 0 0 0 0 0
Level=1G: 32 0 0 0 0 0 0 0 0 0 0
Signed-off-by: Peter Xu <peterx@redhat.com>
Message-Id: <20210730220455.26054-5-peterx@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Introduce kvm_mmu_slot_lpages() to calculcate lpage_info and rmap array size.
The other __kvm_mmu_slot_lpages() can take an extra parameter of npages rather
than fetching from the memslot pointer. Start to use the latter one in
kvm_alloc_memslot_metadata().
Signed-off-by: Peter Xu <peterx@redhat.com>
Message-Id: <20210730220455.26054-4-peterx@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Add yet another spinlock for the TDP MMU and take it when marking indirect
shadow pages unsync. When using the TDP MMU and L1 is running L2(s) with
nested TDP, KVM may encounter shadow pages for the TDP entries managed by
L1 (controlling L2) when handling a TDP MMU page fault. The unsync logic
is not thread safe, e.g. the kvm_mmu_page fields are not atomic, and
misbehaves when a shadow page is marked unsync via a TDP MMU page fault,
which runs with mmu_lock held for read, not write.
Lack of a critical section manifests most visibly as an underflow of
unsync_children in clear_unsync_child_bit() due to unsync_children being
corrupted when multiple CPUs write it without a critical section and
without atomic operations. But underflow is the best case scenario. The
worst case scenario is that unsync_children prematurely hits '0' and
leads to guest memory corruption due to KVM neglecting to properly sync
shadow pages.
Use an entirely new spinlock even though piggybacking tdp_mmu_pages_lock
would functionally be ok. Usurping the lock could degrade performance when
building upper level page tables on different vCPUs, especially since the
unsync flow could hold the lock for a comparatively long time depending on
the number of indirect shadow pages and the depth of the paging tree.
For simplicity, take the lock for all MMUs, even though KVM could fairly
easily know that mmu_lock is held for write. If mmu_lock is held for
write, there cannot be contention for the inner spinlock, and marking
shadow pages unsync across multiple vCPUs will be slow enough that
bouncing the kvm_arch cacheline should be in the noise.
Note, even though L2 could theoretically be given access to its own EPT
entries, a nested MMU must hold mmu_lock for write and thus cannot race
against a TDP MMU page fault. I.e. the additional spinlock only _needs_ to
be taken by the TDP MMU, as opposed to being taken by any MMU for a VM
that is running with the TDP MMU enabled. Holding mmu_lock for read also
prevents the indirect shadow page from being freed. But as above, keep
it simple and always take the lock.
Alternative #1, the TDP MMU could simply pass "false" for can_unsync and
effectively disable unsync behavior for nested TDP. Write protecting leaf
shadow pages is unlikely to noticeably impact traditional L1 VMMs, as such
VMMs typically don't modify TDP entries, but the same may not hold true for
non-standard use cases and/or VMMs that are migrating physical pages (from
L1's perspective).
Alternative #2, the unsync logic could be made thread safe. In theory,
simply converting all relevant kvm_mmu_page fields to atomics and using
atomic bitops for the bitmap would suffice. However, (a) an in-depth audit
would be required, (b) the code churn would be substantial, and (c) legacy
shadow paging would incur additional atomic operations in performance
sensitive paths for no benefit (to legacy shadow paging).
Fixes: a2855afc7e ("KVM: x86/mmu: Allow parallel page faults for the TDP MMU")
Cc: stable@vger.kernel.org
Cc: Ben Gardon <bgardon@google.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20210812181815.3378104-1-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Set the min_level for the TDP iterator at the root level when zapping all
SPTEs to optimize the iterator's try_step_down(). Zapping a non-leaf
SPTE will recursively zap all its children, thus there is no need for the
iterator to attempt to step down. This avoids rereading the top-level
SPTEs after they are zapped by causing try_step_down() to short-circuit.
In most cases, optimizing try_step_down() will be in the noise as the cost
of zapping SPTEs completely dominates the overall time. The optimization
is however helpful if the zap occurs with relatively few SPTEs, e.g. if KVM
is zapping in response to multiple memslot updates when userspace is adding
and removing read-only memslots for option ROMs. In that case, the task
doing the zapping likely isn't a vCPU thread, but it still holds mmu_lock
for read and thus can be a noisy neighbor of sorts.
Reviewed-by: Ben Gardon <bgardon@google.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20210812181414.3376143-3-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Pass "all ones" as the end GFN to signal "zap all" for the TDP MMU and
really zap all SPTEs in this case. As is, zap_gfn_range() skips non-leaf
SPTEs whose range exceeds the range to be zapped. If shadow_phys_bits is
not aligned to the range size of top-level SPTEs, e.g. 512gb with 4-level
paging, the "zap all" flows will skip top-level SPTEs whose range extends
beyond shadow_phys_bits and leak their SPs when the VM is destroyed.
Use the current upper bound (based on host.MAXPHYADDR) to detect that the
caller wants to zap all SPTEs, e.g. instead of using the max theoretical
gfn, 1 << (52 - 12). The more precise upper bound allows the TDP iterator
to terminate its walk earlier when running on hosts with MAXPHYADDR < 52.
Add a WARN on kmv->arch.tdp_mmu_pages when the TDP MMU is destroyed to
help future debuggers should KVM decide to leak SPTEs again.
The bug is most easily reproduced by running (and unloading!) KVM in a
VM whose host.MAXPHYADDR < 39, as the SPTE for gfn=0 will be skipped.
=============================================================================
BUG kvm_mmu_page_header (Not tainted): Objects remaining in kvm_mmu_page_header on __kmem_cache_shutdown()
-----------------------------------------------------------------------------
Slab 0x000000004d8f7af1 objects=22 used=2 fp=0x00000000624d29ac flags=0x4000000000000200(slab|zone=1)
CPU: 0 PID: 1582 Comm: rmmod Not tainted 5.14.0-rc2+ #420
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 0.0.0 02/06/2015
Call Trace:
dump_stack_lvl+0x45/0x59
slab_err+0x95/0xc9
__kmem_cache_shutdown.cold+0x3c/0x158
kmem_cache_destroy+0x3d/0xf0
kvm_mmu_module_exit+0xa/0x30 [kvm]
kvm_arch_exit+0x5d/0x90 [kvm]
kvm_exit+0x78/0x90 [kvm]
vmx_exit+0x1a/0x50 [kvm_intel]
__x64_sys_delete_module+0x13f/0x220
do_syscall_64+0x3b/0xc0
entry_SYSCALL_64_after_hwframe+0x44/0xae
Fixes: faaf05b00a ("kvm: x86/mmu: Support zapping SPTEs in the TDP MMU")
Cc: stable@vger.kernel.org
Cc: Ben Gardon <bgardon@google.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20210812181414.3376143-2-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
gfn_to_rmap was removed in the previous patch so there is no need to
retain the double underscore on __gfn_to_rmap.
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: David Matlack <dmatlack@google.com>
Message-Id: <20210804222844.1419481-7-dmatlack@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
rmap_add() and rmap_recycle() both run in the context of the vCPU and
thus we can use kvm_vcpu_gfn_to_memslot() to look up the memslot. This
enables rmap_add() and rmap_recycle() to take advantage of
vcpu->last_used_slot and avoid expensive memslot searching.
This change improves the performance of "Populate memory time" in
dirty_log_perf_test with tdp_mmu=N. In addition to improving the
performance, "Populate memory time" no longer scales with the number
of memslots in the VM.
Command | Before | After
------------------------------- | ---------------- | -------------
./dirty_log_perf_test -v64 -x1 | 15.18001570s | 14.99469366s
./dirty_log_perf_test -v64 -x64 | 18.71336392s | 14.98675076s
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: David Matlack <dmatlack@google.com>
Message-Id: <20210804222844.1419481-6-dmatlack@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
The existing TDP MMU methods to handle dirty logging are vcpu-agnostic
since they can be driven by MMU notifiers and other non-vcpu-specific
events in addition to page faults. However this means that the TDP MMU
is not benefiting from the new vcpu->last_used_slot. Fix that by
introducing a tdp_mmu_map_set_spte_atomic() which is only called during
a TDP page fault and has access to the kvm_vcpu for fast slot lookups.
This improves "Populate memory time" in dirty_log_perf_test by 5%:
Command | Before | After
------------------------------- | ---------------- | -------------
./dirty_log_perf_test -v64 -x64 | 5.472321072s | 5.169832886s
Signed-off-by: David Matlack <dmatlack@google.com>
Message-Id: <20210804222844.1419481-5-dmatlack@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Take a signed 'long' instead of an 'unsigned long' for the number of
pages to add/subtract to the total number of pages used by the MMU. This
fixes a zero-extension bug on 32-bit kernels that effectively corrupts
the per-cpu counter used by the shrinker.
Per-cpu counters take a signed 64-bit value on both 32-bit and 64-bit
kernels, whereas kvm_mod_used_mmu_pages() takes an unsigned long and thus
an unsigned 32-bit value on 32-bit kernels. As a result, the value used
to adjust the per-cpu counter is zero-extended (unsigned -> signed), not
sign-extended (signed -> signed), and so KVM's intended -1 gets morphed to
4294967295 and effectively corrupts the counter.
This was found by a staggering amount of sheer dumb luck when running
kvm-unit-tests on a 32-bit KVM build. The shrinker just happened to kick
in while running tests and do_shrink_slab() logged an error about trying
to free a negative number of objects. The truly lucky part is that the
kernel just happened to be a slightly stale build, as the shrinker no
longer yells about negative objects as of commit 18bb473e50 ("mm:
vmscan: shrink deferred objects proportional to priority").
vmscan: shrink_slab: mmu_shrink_scan+0x0/0x210 [kvm] negative objects to delete nr=-858993460
Fixes: bc8a3d8925 ("kvm: mmu: Fix overflow on kvm mmu page limit calculation")
Cc: stable@vger.kernel.org
Cc: Ben Gardon <bgardon@google.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20210804214609.1096003-1-seanjc@google.com>
Reviewed-by: Jim Mattson <jmattson@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Using rmap_get_first() and rmap_remove() for zapping a huge rmap list could be
slow. The easy way is to travers the rmap list, collecting the a/d bits and
free the slots along the way.
Provide a pte_list_destroy() and do exactly that.
Signed-off-by: Peter Xu <peterx@redhat.com>
Message-Id: <20210730220605.26377-1-peterx@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
