From 79e48cec6cba4eee0bd3a13f31320e33a1729931 Mon Sep 17 00:00:00 2001 From: Sean Christopherson Date: Tue, 12 Jul 2022 02:07:22 +0000 Subject: [PATCH] KVM: x86/mmu: Add optimized helper to retrieve an SPTE's index 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 Reviewed-by: David Matlack Signed-off-by: Sean Christopherson Message-Id: <20220712020724.1262121-2-seanjc@google.com> Signed-off-by: Paolo Bonzini --- arch/x86/kvm/mmu/mmu.c | 22 ++++++++++------------ arch/x86/kvm/mmu/paging_tmpl.h | 4 ++-- arch/x86/kvm/mmu/spte.h | 6 ++++++ 3 files changed, 18 insertions(+), 14 deletions(-) diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c index f7fa4c3..864a32f 100644 --- a/arch/x86/kvm/mmu/mmu.c +++ b/arch/x86/kvm/mmu/mmu.c @@ -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; diff --git a/arch/x86/kvm/mmu/paging_tmpl.h b/arch/x86/kvm/mmu/paging_tmpl.h index 94bfd5f..f595807 100644 --- a/arch/x86/kvm/mmu/paging_tmpl.h +++ b/arch/x86/kvm/mmu/paging_tmpl.h @@ -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)) diff --git a/arch/x86/kvm/mmu/spte.h b/arch/x86/kvm/mmu/spte.h index b5c855f..ba3dccb 100644 --- a/arch/x86/kvm/mmu/spte.h +++ b/arch/x86/kvm/mmu/spte.h @@ -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 -- 2.7.4