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KVM: x86/mmu: Add optimized helper to retrieve an SPTE's index

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Add spte_index() to dedup all the code that calculates a SPTE's index
into its parent's page table and/or spt array.  Opportunistically tweak
the calculation to avoid pointer arithmetic, which is subtle (subtract in
8-byte chunks) and less performant (requires the compiler to generate the
subtraction).

Suggested-by: David Matlack <dmatlack@google.com>
Reviewed-by: David Matlack <dmatlack@google.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20220712020724.1262121-2-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Sean Christopherson 2022-07-12 02:07:22 +00:00 committed by Paolo Bonzini
parent b184b35d06
commit 79e48cec6c
3 changed files with 18 additions and 14 deletions
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22
arch/x86/kvm/mmu/mmu.c
View File

@ -1038,7 +1038,7 @@ static void rmap_remove(struct kvm *kvm, u64 *spte)
struct kvm_rmap_head *rmap_head;
sp = sptep_to_sp(spte);
gfn = kvm_mmu_page_get_gfn(sp, spte - sp->spt);
gfn = kvm_mmu_page_get_gfn(sp, spte_index(spte));
/*
* Unlike rmap_add, rmap_remove does not run in the context of a vCPU
@ -1589,7 +1589,7 @@ static void __rmap_add(struct kvm *kvm,
int rmap_count;
sp = sptep_to_sp(spte);
kvm_mmu_page_set_translation(sp, spte - sp->spt, gfn, access);
kvm_mmu_page_set_translation(sp, spte_index(spte), gfn, access);
kvm_update_page_stats(kvm, sp->role.level, 1);
rmap_head = gfn_to_rmap(gfn, sp->role.level, slot);
@ -1716,11 +1716,9 @@ static void kvm_mmu_mark_parents_unsync(struct kvm_mmu_page *sp)
static void mark_unsync(u64 *spte)
{
struct kvm_mmu_page *sp;
unsigned int index;
sp = sptep_to_sp(spte);
index = spte - sp->spt;
if (__test_and_set_bit(index, sp->unsync_child_bitmap))
if (__test_and_set_bit(spte_index(spte), sp->unsync_child_bitmap))
return;
if (sp->unsync_children++)
return;
@ -2203,7 +2201,7 @@ static union kvm_mmu_page_role kvm_mmu_child_role(u64 *sptep, bool direct, unsig
*/
if (role.has_4_byte_gpte) {
WARN_ON_ONCE(role.level != PG_LEVEL_4K);
role.quadrant = (sptep - parent_sp->spt) % 2;
role.quadrant = spte_index(sptep) & 1;
}
return role;
@ -2828,7 +2826,7 @@ static int mmu_set_spte(struct kvm_vcpu *vcpu, struct kvm_memory_slot *slot,
rmap_add(vcpu, slot, sptep, gfn, pte_access);
} else {
/* Already rmapped but the pte_access bits may have changed. */
kvm_mmu_page_set_access(sp, sptep - sp->spt, pte_access);
kvm_mmu_page_set_access(sp, spte_index(sptep), pte_access);
}
return ret;
@ -2844,7 +2842,7 @@ static int direct_pte_prefetch_many(struct kvm_vcpu *vcpu,
int i, ret;
gfn_t gfn;
gfn = kvm_mmu_page_get_gfn(sp, start - sp->spt);
gfn = kvm_mmu_page_get_gfn(sp, spte_index(start));
slot = gfn_to_memslot_dirty_bitmap(vcpu, gfn, access & ACC_WRITE_MASK);
if (!slot)
return -1;
@ -2870,7 +2868,7 @@ static void __direct_pte_prefetch(struct kvm_vcpu *vcpu,
WARN_ON(!sp->role.direct);
i = (sptep - sp->spt) & ~(PTE_PREFETCH_NUM - 1);
i = spte_index(sptep) & ~(PTE_PREFETCH_NUM - 1);
spte = sp->spt + i;
for (i = 0; i < PTE_PREFETCH_NUM; i++, spte++) {
@ -6156,8 +6154,8 @@ static struct kvm_mmu_page *shadow_mmu_get_sp_for_split(struct kvm *kvm, u64 *hu
unsigned int access;
gfn_t gfn;
gfn = kvm_mmu_page_get_gfn(huge_sp, huge_sptep - huge_sp->spt);
access = kvm_mmu_page_get_access(huge_sp, huge_sptep - huge_sp->spt);
gfn = kvm_mmu_page_get_gfn(huge_sp, spte_index(huge_sptep));
access = kvm_mmu_page_get_access(huge_sp, spte_index(huge_sptep));
/*
* Note, huge page splitting always uses direct shadow pages, regardless
@ -6231,7 +6229,7 @@ static int shadow_mmu_try_split_huge_page(struct kvm *kvm,
u64 spte;
/* Grab information for the tracepoint before dropping the MMU lock. */
gfn = kvm_mmu_page_get_gfn(huge_sp, huge_sptep - huge_sp->spt);
gfn = kvm_mmu_page_get_gfn(huge_sp, spte_index(huge_sptep));
level = huge_sp->role.level;
spte = *huge_sptep;

4
arch/x86/kvm/mmu/paging_tmpl.h
View File

@ -595,7 +595,7 @@ static void FNAME(pte_prefetch)(struct kvm_vcpu *vcpu, struct guest_walker *gw,
if (sp->role.direct)
return __direct_pte_prefetch(vcpu, sp, sptep);
i = (sptep - sp->spt) & ~(PTE_PREFETCH_NUM - 1);
i = spte_index(sptep) & ~(PTE_PREFETCH_NUM - 1);
spte = sp->spt + i;
for (i = 0; i < PTE_PREFETCH_NUM; i++, spte++) {
@ -933,7 +933,7 @@ static void FNAME(invlpg)(struct kvm_vcpu *vcpu, gva_t gva, hpa_t root_hpa)
break;
pte_gpa = FNAME(get_level1_sp_gpa)(sp);
pte_gpa += (sptep - sp->spt) * sizeof(pt_element_t);
pte_gpa += spte_index(sptep) * sizeof(pt_element_t);
mmu_page_zap_pte(vcpu->kvm, sp, sptep, NULL);
if (is_shadow_present_pte(old_spte))

6
arch/x86/kvm/mmu/spte.h
View File

@ -190,6 +190,12 @@ static inline bool is_removed_spte(u64 spte)
return spte == REMOVED_SPTE;
}
/* Get an SPTE's index into its parent's page table (and the spt array). */
static inline int spte_index(u64 *sptep)
{
return ((unsigned long)sptep / sizeof(*sptep)) & (SPTE_ENT_PER_PAGE - 1);
}
/*
* In some cases, we need to preserve the GFN of a non-present or reserved
* SPTE when we usurp the upper five bits of the physical address space to