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KVM: x86/mmu: Remove FNAME(is_self_change_mapping)

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Drop FNAME(is_self_change_mapping) and instead rely on
kvm_mmu_hugepage_adjust() to adjust the hugepage accordingly.  Prior to
commit 4cd071d13c ("KVM: x86/mmu: Move calls to thp_adjust() down a
level"), the hugepage adjustment was done before allocating new shadow
pages, i.e. failed to restrict the hugepage sizes if a new shadow page
resulted in account_shadowed() changing the disallowed hugepage tracking.

Removing FNAME(is_self_change_mapping) fixes a bug reported by Huang Hang
where KVM unnecessarily forces a 4KiB page.  FNAME(is_self_change_mapping)
has a defect in that it blindly disables _all_ hugepage mappings rather
than trying to reduce the size of the hugepage.  If the guest is writing
to a 1GiB page and the 1GiB is self-referential but a 2MiB page is not,
then KVM can and should create a 2MiB mapping.

Add a comment above the call to kvm_mmu_hugepage_adjust() to call out the
new dependency on adjusting the hugepage size after walking indirect PTEs.

Reported-by: Huang Hang <hhuang@linux.alibaba.com>
Signed-off-by: Lai Jiangshan <jiangshan.ljs@antgroup.com>
Link: https://lore.kernel.org/r/20221213125538.81209-1-jiangshanlai@gmail.com
[sean: rework changelog after separating out the emulator change]
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20230202182817.407394-4-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Lai Jiangshan 2023-02-02 18:28:17 +00:00 committed by Paolo Bonzini
parent 39fda5d873
commit 9a96770049
1 changed files with 7 additions and 44 deletions
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51
arch/x86/kvm/mmu/paging_tmpl.h
View File

@ -690,6 +690,12 @@ static int FNAME(fetch)(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault,
fault->write_fault_to_shadow_pgtable = true;
}
/*
* Adjust the hugepage size _after_ resolving indirect shadow pages.
* KVM doesn't support mapping hugepages into the guest for gfns that
* are being shadowed by KVM, i.e. allocating a new shadow page may
* affect the allowed hugepage size.
*/
kvm_mmu_hugepage_adjust(vcpu, fault);
trace_kvm_mmu_spte_requested(fault);
@ -734,41 +740,6 @@ out_gpte_changed:
return RET_PF_RETRY;
}
/*
* To see whether the mapped gfn can write its page table in the current
* mapping.
*
* It is the helper function of FNAME(page_fault). When guest uses large page
* size to map the writable gfn which is used as current page table, we should
* force kvm to use small page size to map it because new shadow page will be
* created when kvm establishes shadow page table that stop kvm using large
* page size. Do it early can avoid unnecessary #PF and emulation.
*
* Note: the PDPT page table is not checked for PAE-32 bit guest. It is ok
* since the PDPT is always shadowed, that means, we can not use large page
* size to map the gfn which is used as PDPT.
*/
static bool
FNAME(is_self_change_mapping)(struct kvm_vcpu *vcpu,
struct guest_walker *walker, bool user_fault)
{
int level;
gfn_t mask = ~(KVM_PAGES_PER_HPAGE(walker->level) - 1);
bool self_changed = false;
if (!(walker->pte_access & ACC_WRITE_MASK ||
(!is_cr0_wp(vcpu->arch.mmu) && !user_fault)))
return false;
for (level = walker->level; level <= walker->max_level; level++) {
gfn_t gfn = walker->gfn ^ walker->table_gfn[level - 1];
self_changed |= !(gfn & mask);
}
return self_changed;
}
/*
* Page fault handler. There are several causes for a page fault:
* - there is no shadow pte for the guest pte
@ -787,7 +758,6 @@ static int FNAME(page_fault)(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault
{
struct guest_walker walker;
int r;
bool is_self_change_mapping;
pgprintk("%s: addr %lx err %x\n", __func__, fault->addr, fault->error_code);
WARN_ON_ONCE(fault->is_tdp);
@ -812,6 +782,7 @@ static int FNAME(page_fault)(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault
}
fault->gfn = walker.gfn;
fault->max_level = walker.level;
fault->slot = kvm_vcpu_gfn_to_memslot(vcpu, fault->gfn);
if (page_fault_handle_page_track(vcpu, fault)) {
@ -823,14 +794,6 @@ static int FNAME(page_fault)(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault
if (r)
return r;
is_self_change_mapping = FNAME(is_self_change_mapping)(vcpu,
&walker, fault->user);
if (is_self_change_mapping)
fault->max_level = PG_LEVEL_4K;
else
fault->max_level = walker.level;
r = kvm_faultin_pfn(vcpu, fault, walker.pte_access);
if (r != RET_PF_CONTINUE)
return r;