raspi/linux
1
0
Fork 1
mirror of https://github.com/raspberrypi/linux.git synced 2025-12-27 12:32:50 +00:00
Code Issues Projects Releases Wiki Activity

KVM: x86/mmu: Use Accessed bit even when _hardware_ A/D bits are disabled

Browse Source 
Use the Accessed bit in SPTEs even when A/D bits are disabled in hardware,
i.e. propagate accessed information to SPTE.Accessed even when KVM is
doing manual tracking by making SPTEs not-present.  In addition to
eliminating a small amount of code in is_accessed_spte(), this also paves
the way for preserving Accessed information when a SPTE is zapped in
response to a mmu_notifier PROTECTION event, e.g. if a SPTE is zapped
because NUMA balancing kicks in.

Note, EPT is the only flavor of paging in which A/D bits are conditionally
enabled, and the Accessed (and Dirty) bit is software-available when A/D
bits are disabled.

Note #2, there are currently no concrete plans to preserve Accessed
information.  Explorations on that front were the initial catalyst, but
the cleanup is the motivation for the actual commit.

Link: https://lore.kernel.org/r/20241011021051.1557902-13-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>
This commit is contained in:
Sean Christopherson
2024-10-10 19:10:44 -07:00
parent 53510b9125
commit 7971801b56
3 changed files with 5 additions and 13 deletions
Download Patch File Download Diff File Expand all files Collapse all files

3
arch/x86/kvm/mmu/mmu.c
View File

@@ -3493,7 +3493,8 @@ static int fast_page_fault(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault)
* enabled, the SPTE can't be an access-tracked SPTE.
*/
if (unlikely(!kvm_ad_enabled) && is_access_track_spte(spte))
new_spte = restore_acc_track_spte(new_spte);
new_spte = restore_acc_track_spte(new_spte) |
shadow_accessed_mask;
/*
* To keep things simple, only SPTEs that are MMU-writable can

4
arch/x86/kvm/mmu/spte.c
View File

@@ -175,7 +175,7 @@ bool make_spte(struct kvm_vcpu *vcpu, struct kvm_mmu_page *sp,
spte |= shadow_present_mask;
if (!prefetch || synchronizing)
spte |= spte_shadow_accessed_mask(spte);
spte |= shadow_accessed_mask;
/*
* For simplicity, enforce the NX huge page mitigation even if not
@@ -346,7 +346,7 @@ u64 mark_spte_for_access_track(u64 spte)
spte |= (spte & SHADOW_ACC_TRACK_SAVED_BITS_MASK) <<
SHADOW_ACC_TRACK_SAVED_BITS_SHIFT;
spte &= ~shadow_acc_track_mask;
spte &= ~(shadow_acc_track_mask | shadow_accessed_mask);
return spte;
}

11
arch/x86/kvm/mmu/spte.h
View File

@@ -316,12 +316,6 @@ static inline bool spte_ad_need_write_protect(u64 spte)
return (spte & SPTE_TDP_AD_MASK) != SPTE_TDP_AD_ENABLED;
}
static inline u64 spte_shadow_accessed_mask(u64 spte)
{
KVM_MMU_WARN_ON(!is_shadow_present_pte(spte));
return spte_ad_enabled(spte) ? shadow_accessed_mask : 0;
}
static inline u64 spte_shadow_dirty_mask(u64 spte)
{
KVM_MMU_WARN_ON(!is_shadow_present_pte(spte));
@@ -355,10 +349,7 @@ static inline kvm_pfn_t spte_to_pfn(u64 pte)
static inline bool is_accessed_spte(u64 spte)
{
u64 accessed_mask = spte_shadow_accessed_mask(spte);
return accessed_mask ? spte & accessed_mask
: !is_access_track_spte(spte);
return spte & shadow_accessed_mask;
}
static inline u64 get_rsvd_bits(struct rsvd_bits_validate *rsvd_check, u64 pte,