mirrors/linux
2
0
Fork 0
mirror of https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git synced 2026-05-07 22:08:33 -04:00
Code Issues Packages Projects Releases Wiki Activity

KVM: x86/mmu: Move shadow-present check out of spte_has_volatile_bits()

Browse Source 
Move the is_shadow_present_pte() check out of spte_has_volatile_bits()
and into its callers.  Well, caller, since only one of its two callers
doesn't already do the shadow-present check.

Opportunistically move the helper to spte.c/h so that it can be used by
the TDP MMU, which is also the primary motivation for the shadow-present
change.  Unlike the legacy MMU, the TDP MMU uses a single path for clear
leaf and non-leaf SPTEs, and to avoid unnecessary atomic updates, the TDP
MMU will need to check is_last_spte() prior to calling
spte_has_volatile_bits(), and calling is_last_spte() without first
calling is_shadow_present_spte() is at best odd, and at worst a violation
of KVM's loosely defines SPTE rules.

Note, mmu_spte_clear_track_bits() could likely skip the write entirely
for SPTEs that are not shadow-present.  Leave that cleanup for a future
patch to avoid introducing a functional change, and because the
shadow-present check can likely be moved further up the stack, e.g.
drop_large_spte() appears to be the only path that doesn't already
explicitly check for a shadow-present SPTE.

No functional change intended.

Cc: stable@vger.kernel.org
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20220423034752.1161007-3-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Sean Christopherson
2022-04-23 03:47:42 +00:00
committed by Paolo Bonzini
parent 706c9c55e5
commit 54eb3ef56f
3 changed files with 32 additions and 27 deletions
Download Patch File Download Diff File Expand all files Collapse all files

29
arch/x86/kvm/mmu/mmu.c
View File

@@ -473,32 +473,6 @@ static u64 __get_spte_lockless(u64 *sptep)
}
#endif
static bool spte_has_volatile_bits(u64 spte)
{
if (!is_shadow_present_pte(spte))
return false;
/*
* Always atomically update spte if it can be updated
* out of mmu-lock, it can ensure dirty bit is not lost,
* also, it can help us to get a stable is_writable_pte()
* to ensure tlb flush is not missed.
*/
if (!is_writable_pte(spte) && is_mmu_writable_spte(spte))
return true;
if (is_access_track_spte(spte))
return true;
if (spte_ad_enabled(spte)) {
if (!(spte & shadow_accessed_mask) ||
(is_writable_pte(spte) && !(spte & shadow_dirty_mask)))
return true;
}
return false;
}
/* Rules for using mmu_spte_set:
* Set the sptep from nonpresent to present.
* Note: the sptep being assigned *must* be either not present
@@ -593,7 +567,8 @@ static int mmu_spte_clear_track_bits(struct kvm *kvm, u64 *sptep)
u64 old_spte = *sptep;
int level = sptep_to_sp(sptep)->role.level;
if (!spte_has_volatile_bits(old_spte))
if (!is_shadow_present_pte(old_spte) ||
!spte_has_volatile_bits(old_spte))
__update_clear_spte_fast(sptep, 0ull);
else
old_spte = __update_clear_spte_slow(sptep, 0ull);

28
arch/x86/kvm/mmu/spte.c
View File

@@ -90,6 +90,34 @@ static bool kvm_is_mmio_pfn(kvm_pfn_t pfn)
E820_TYPE_RAM);
}
/*
* Returns true if the SPTE has bits that may be set without holding mmu_lock.
* The caller is responsible for checking if the SPTE is shadow-present, and
* for determining whether or not the caller cares about non-leaf SPTEs.
*/
bool spte_has_volatile_bits(u64 spte)
{
/*
* Always atomically update spte if it can be updated
* out of mmu-lock, it can ensure dirty bit is not lost,
* also, it can help us to get a stable is_writable_pte()
* to ensure tlb flush is not missed.
*/
if (!is_writable_pte(spte) && is_mmu_writable_spte(spte))
return true;
if (is_access_track_spte(spte))
return true;
if (spte_ad_enabled(spte)) {
if (!(spte & shadow_accessed_mask) ||
(is_writable_pte(spte) && !(spte & shadow_dirty_mask)))
return true;
}
return false;
}
bool make_spte(struct kvm_vcpu *vcpu, struct kvm_mmu_page *sp,
const struct kvm_memory_slot *slot,
unsigned int pte_access, gfn_t gfn, kvm_pfn_t pfn,

2
arch/x86/kvm/mmu/spte.h
View File

@@ -404,6 +404,8 @@ static inline u64 get_mmio_spte_generation(u64 spte)
return gen;
}
bool spte_has_volatile_bits(u64 spte);
bool make_spte(struct kvm_vcpu *vcpu, struct kvm_mmu_page *sp,
const struct kvm_memory_slot *slot,
unsigned int pte_access, gfn_t gfn, kvm_pfn_t pfn,