diff options
| author | James Houghton <jthoughton@google.com> | 2025-02-04 00:40:32 +0000 |
|---|---|---|
| committer | Sean Christopherson <seanjc@google.com> | 2025-02-14 07:16:45 -0800 |
| commit | 61d65f2dc766c70673d45a4b787f49317384642c (patch) | |
| tree | b664abf8e2b7ffdf15aae5d75ddb95ee74f50b76 /Documentation/virt/kvm/locking.rst | |
| parent | e29b74920e6f0e5a8a26f373b821a3a3e79ceb9a (diff) | |
KVM: x86/mmu: Don't force atomic update if only the Accessed bit is volatile
Don't force SPTE modifications to be done atomically if the only volatile
bit in the SPTE is the Accessed bit. KVM and the primary MMU tolerate
stale aging state, and the probability of an Accessed bit A/D assist being
clobbered *and* affecting again is likely far lower than the probability
of consuming stale information due to not flushing TLBs when aging.
Rename spte_has_volatile_bits() to spte_needs_atomic_update() to better
capture the nature of the helper.
Opportunstically do s/write/update on the TDP MMU wrapper, as it's not
simply the "write" that needs to be done atomically, it's the entire
update, i.e. the entire read-modify-write operation needs to be done
atomically so that KVM has an accurate view of the old SPTE.
Leave kvm_tdp_mmu_write_spte_atomic() as is. While the name is imperfect,
it pairs with kvm_tdp_mmu_write_spte(), which in turn pairs with
kvm_tdp_mmu_read_spte(). And renaming all of those isn't obviously a net
positive, and would require significant churn.
Signed-off-by: James Houghton <jthoughton@google.com>
Link: https://lore.kernel.org/r/20250204004038.1680123-6-jthoughton@google.com
Co-developed-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>
Diffstat (limited to 'Documentation/virt/kvm/locking.rst')
| -rw-r--r-- | Documentation/virt/kvm/locking.rst | 4 |
1 files changed, 2 insertions, 2 deletions
diff --git a/Documentation/virt/kvm/locking.rst b/Documentation/virt/kvm/locking.rst index c56d5f26c750..ae8bce7fecbe 100644 --- a/Documentation/virt/kvm/locking.rst +++ b/Documentation/virt/kvm/locking.rst @@ -196,7 +196,7 @@ writable between reading spte and updating spte. Like below case: The Dirty bit is lost in this case. In order to avoid this kind of issue, we always treat the spte as "volatile" -if it can be updated out of mmu-lock [see spte_has_volatile_bits()]; it means +if it can be updated out of mmu-lock [see spte_needs_atomic_update()]; it means the spte is always atomically updated in this case. 3) flush tlbs due to spte updated @@ -212,7 +212,7 @@ function to update spte (present -> present). Since the spte is "volatile" if it can be updated out of mmu-lock, we always atomically update the spte and the race caused by fast page fault can be avoided. -See the comments in spte_has_volatile_bits() and mmu_spte_update(). +See the comments in spte_needs_atomic_update() and mmu_spte_update(). Lockless Access Tracking: |