Use low "available" bits to tag REMOVED SPTEs. Using a high bit is
moderately costly as it often causes the compiler to generate a 64-bit
immediate. More importantly, this makes it very clear REMOVED_SPTE is
a value, not a flag.
Cc: Ben Gardon <bgardon@google.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20210225204749.1512652-24-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Tweak the MMU_WARN that guards against weirdness when querying A/D status
to fire on a !MMU_PRESENT SPTE, as opposed to a MMIO SPTE. Attempting to
query A/D status on any kind of !MMU_PRESENT SPTE, MMIO or otherwise,
indicates a KVM bug. Case in point, several now-fixed bugs were
identified by enabling this new WARN.
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20210225204749.1512652-22-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Introduce MMU_PRESENT to explicitly track which SPTEs are "present" from
the MMU's perspective. Checking for shadow-present SPTEs is a very
common operation for the MMU, particularly in hot paths such as page
faults. With the addition of "removed" SPTEs for the TDP MMU,
identifying shadow-present SPTEs is quite costly especially since it
requires checking multiple 64-bit values.
On 64-bit KVM, this reduces the footprint of kvm.ko's .text by ~2k bytes.
On 32-bit KVM, this increases the footprint by ~200 bytes, but only
because gcc now inlines several more MMU helpers, e.g. drop_parent_pte().
We now need to drop bit 11, used for the MMU_PRESENT flag, from
the set of bits used to store the generation number in MMIO SPTEs.
Otherwise MMIO SPTEs with bit 11 set would get false positives for
is_shadow_present_spte() and lead to a variety of fireworks, from oopses
to likely hangs of the host kernel.
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20210225204749.1512652-21-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Use bits 57 and 58 for HOST_WRITABLE and MMU_WRITABLE when using EPT.
This will allow using bit 11 as a constant MMU_PRESENT, which is
desirable as checking for a shadow-present SPTE is one of the most
common SPTE operations in KVM, particular in hot paths such as page
faults.
EPT is short on low available bits; currently only bit 11 is the only
always-available bit. Bit 10 is also available, but only while KVM
doesn't support mode-based execution. On the other hand, PAE paging
doesn't have _any_ high available bits. Thus, using bit 11 is the only
feasible option for MMU_PRESENT.
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20210225204749.1512652-20-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Make the location of the HOST_WRITABLE and MMU_WRITABLE configurable for
a given KVM instance. This will allow EPT to use high available bits,
which in turn will free up bit 11 for a constant MMU_PRESENT bit.
No functional change intended.
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20210225204749.1512652-19-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Document that SHADOW_ACC_TRACK_SAVED_BITS_SHIFT is directly dependent on
bits 53:52 being used to track the A/D type.
Remove PT64_SECOND_AVAIL_BITS_SHIFT as it is at best misleading, and at
worst wrong. For PAE paging, which arguably is a variant of PT64, the
bits are reserved. For MMIO SPTEs the bits are not available as they're
used for the MMIO generation. For access tracked SPTEs, they are also
not available as bits 56:54 are used to store the original RX bits.
No functional change intended.
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20210225204749.1512652-15-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Use bits 53 and 52 for the MMIO generation now that they're not used to
identify MMIO SPTEs.
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20210225204749.1512652-14-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Rename the various A/D status defines to explicitly associated them with
TDP. There is a subtle dependency on the bits in question never being
set when using PAE paging, as those bits are reserved, not available.
I.e. using these bits outside of TDP (technically EPT) would cause
explosions.
No functional change intended.
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20210225204749.1512652-13-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Stop tagging MMIO SPTEs with specific available bits and instead detect
MMIO SPTEs by checking for their unique SPTE value. The value is
guaranteed to be unique on shadow paging and NPT as setting reserved
physical address bits on any other type of SPTE would consistute a KVM
bug. Ditto for EPT, as creating a WX non-MMIO would also be a bug.
Note, this approach is also future-compatibile with TDX, which will need
to reflect MMIO EPT violations as #VEs into the guest. To create an EPT
violation instead of a misconfig, TDX EPTs will need to have RWX=0, But,
MMIO SPTEs will also be the only case where KVM clears SUPPRESS_VE, so
MMIO SPTEs will still be guaranteed to have a unique value within a given
MMU context.
The main motivation is to make it easier to reason about which types of
SPTEs use which available bits. As a happy side effect, this frees up
two more bits for storing the MMIO generation.
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20210225204749.1512652-11-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
When the TDP MMU is allowed to handle page faults in parallel there is
the possiblity of a race where an SPTE is cleared and then imediately
replaced with a present SPTE pointing to a different PFN, before the
TLBs can be flushed. This race would violate architectural specs. Ensure
that the TLBs are flushed properly before other threads are allowed to
install any present value for the SPTE.
Reviewed-by: Peter Feiner <pfeiner@google.com>
Signed-off-by: Ben Gardon <bgardon@google.com>
Message-Id: <20210202185734.1680553-22-bgardon@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Return a 'bool' instead of an 'int' for various PTE accessors that are
boolean in nature, e.g. is_shadow_present_pte(). Returning an int is
goofy and potentially dangerous, e.g. if a flag being checked is moved
into the upper 32 bits of a SPTE, then the compiler may silently squash
the entire check since casting to an int is guaranteed to yield a
return value of '0'.
Opportunistically refactor is_last_spte() so that it naturally returns
a bool value instead of letting it implicitly cast 0/1 to false/true.
No functional change intended.
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20210123003003.3137525-1-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Commit cae7ed3c2c ("KVM: x86: Refactor the MMIO SPTE generation handling")
cleaned up the computation of MMIO generation SPTE masks, however it
introduced a bug how the upper part was encoded:
SPTE bits 52-61 were supposed to contain bits 10-19 of the current
generation number, however a missing shift encoded bits 1-10 there instead
(mostly duplicating the lower part of the encoded generation number that
then consisted of bits 1-9).
In the meantime, the upper part was shrunk by one bit and moved by
subsequent commits to become an upper half of the encoded generation number
(bits 9-17 of bits 0-17 encoded in a SPTE).
In addition to the above, commit 56871d444b ("KVM: x86: fix overlap between SPTE_MMIO_MASK and generation")
has changed the SPTE bit range assigned to encode the generation number and
the total number of bits encoded but did not update them in the comment
attached to their defines, nor in the KVM MMU doc.
Let's do it here, too, since it is too trivial thing to warrant a separate
commit.
Fixes: cae7ed3c2c ("KVM: x86: Refactor the MMIO SPTE generation handling")
Signed-off-by: Maciej S. Szmigiero <maciej.szmigiero@oracle.com>
Message-Id: <156700708db2a5296c5ed7a8b9ac71f1e9765c85.1607129096.git.maciej.szmigiero@oracle.com>
Cc: stable@vger.kernel.org
[Reorganize macros so that everything is computed from the bit ranges. - Paolo]
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Even though the compiler is able to replace static const variables with
their value, it will warn about them being unused when Linux is built with W=1.
Use good old macros instead, this is not C++.
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
The SPTE format will be common to both the shadow and the TDP MMU.
Extract code that implements the format to a separate module, as a
first step towards adding the TDP MMU and putting mmu.c on a diet.
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
