Merge branch 'kvm-tdp-mmu-atomicity-fix' into HEAD

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We are dropping A/D bits (and W bits) in the TDP MMU.  Even if mmu_lock
is held for write, as volatile SPTEs can be written by other tasks/vCPUs
outside of mmu_lock.

Attempting to prove that bug exposed another notable goof, which has been
lurking for a decade, give or take: KVM treats _all_ MMU-writable SPTEs
as volatile, even though KVM never clears WRITABLE outside of MMU lock.
As a result, the legacy MMU (and the TDP MMU if not fixed) uses XCHG to
update writable SPTEs.

The fix does not seem to have an easily-measurable affect on performance;
page faults are so slow that wasting even a few hundred cycles is dwarfed
by the base cost.

...

This commit is contained in:

Paolo Bonzini 2022-05-03 07:23:08 -04:00

parent f751d8eac1 ba3a6120a4

commit 4f510c8bb1

5 changed files with 121 additions and 61 deletions

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34

arch/x86/kvm/mmu/mmu.c

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28

arch/x86/kvm/mmu/spte.c

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4

arch/x86/kvm/mmu/spte.h

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34

arch/x86/kvm/mmu/tdp_iter.h

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82

arch/x86/kvm/mmu/tdp_mmu.c

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