From 6bb69c9b69c315200ddc2bc79aee14c0184cf5b2 Mon Sep 17 00:00:00 2001 From: Paolo Bonzini Date: Tue, 23 Feb 2016 12:51:19 +0100 Subject: [PATCH] KVM: MMU: simplify last_pte_bitmap Branch-free code is fun and everybody knows how much Avi loves it, but last_pte_bitmap takes it a bit to the extreme. Since the code is simply doing a range check, like (level == 1 || ((gpte & PT_PAGE_SIZE_MASK) && level < N) we can make it branch-free without storing the entire truth table; it is enough to cache N. Signed-off-by: Paolo Bonzini --- arch/x86/include/asm/kvm_host.h | 8 ++----- arch/x86/kvm/mmu.c | 50 +++++++++++++++++++++-------------------- 2 files changed, 28 insertions(+), 30 deletions(-) diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h index 1c3e390..d110dc4 100644 --- a/arch/x86/include/asm/kvm_host.h +++ b/arch/x86/include/asm/kvm_host.h @@ -347,12 +347,8 @@ struct kvm_mmu { struct rsvd_bits_validate guest_rsvd_check; - /* - * Bitmap: bit set = last pte in walk - * index[0:1]: level (zero-based) - * index[2]: pte.ps - */ - u8 last_pte_bitmap; + /* Can have large pages at levels 2..last_nonleaf_level-1. */ + u8 last_nonleaf_level; bool nx; diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c index 754d2c4..2463de0 100644 --- a/arch/x86/kvm/mmu.c +++ b/arch/x86/kvm/mmu.c @@ -3632,13 +3632,24 @@ static bool sync_mmio_spte(struct kvm_vcpu *vcpu, u64 *sptep, gfn_t gfn, return false; } -static inline bool is_last_gpte(struct kvm_mmu *mmu, unsigned level, unsigned gpte) +static inline bool is_last_gpte(struct kvm_mmu *mmu, + unsigned level, unsigned gpte) { - unsigned index; + /* + * PT_PAGE_TABLE_LEVEL always terminates. The RHS has bit 7 set + * iff level <= PT_PAGE_TABLE_LEVEL, which for our purpose means + * level == PT_PAGE_TABLE_LEVEL; set PT_PAGE_SIZE_MASK in gpte then. + */ + gpte |= level - PT_PAGE_TABLE_LEVEL - 1; - index = level - 1; - index |= (gpte & PT_PAGE_SIZE_MASK) >> (PT_PAGE_SIZE_SHIFT - 2); - return mmu->last_pte_bitmap & (1 << index); + /* + * The RHS has bit 7 set iff level < mmu->last_nonleaf_level. + * If it is clear, there are no large pages at this level, so clear + * PT_PAGE_SIZE_MASK in gpte if that is the case. + */ + gpte &= level - mmu->last_nonleaf_level; + + return gpte & PT_PAGE_SIZE_MASK; } #define PTTYPE_EPT 18 /* arbitrary */ @@ -3910,22 +3921,13 @@ static void update_permission_bitmask(struct kvm_vcpu *vcpu, } } -static void update_last_pte_bitmap(struct kvm_vcpu *vcpu, struct kvm_mmu *mmu) +static void update_last_nonleaf_level(struct kvm_vcpu *vcpu, struct kvm_mmu *mmu) { - u8 map; - unsigned level, root_level = mmu->root_level; - const unsigned ps_set_index = 1 << 2; /* bit 2 of index: ps */ - - if (root_level == PT32E_ROOT_LEVEL) - --root_level; - /* PT_PAGE_TABLE_LEVEL always terminates */ - map = 1 | (1 << ps_set_index); - for (level = PT_DIRECTORY_LEVEL; level <= root_level; ++level) { - if (level <= PT_PDPE_LEVEL - && (mmu->root_level >= PT32E_ROOT_LEVEL || is_pse(vcpu))) - map |= 1 << (ps_set_index | (level - 1)); - } - mmu->last_pte_bitmap = map; + unsigned root_level = mmu->root_level; + + mmu->last_nonleaf_level = root_level; + if (root_level == PT32_ROOT_LEVEL && is_pse(vcpu)) + mmu->last_nonleaf_level++; } static void paging64_init_context_common(struct kvm_vcpu *vcpu, @@ -3937,7 +3939,7 @@ static void paging64_init_context_common(struct kvm_vcpu *vcpu, reset_rsvds_bits_mask(vcpu, context); update_permission_bitmask(vcpu, context, false); - update_last_pte_bitmap(vcpu, context); + update_last_nonleaf_level(vcpu, context); MMU_WARN_ON(!is_pae(vcpu)); context->page_fault = paging64_page_fault; @@ -3964,7 +3966,7 @@ static void paging32_init_context(struct kvm_vcpu *vcpu, reset_rsvds_bits_mask(vcpu, context); update_permission_bitmask(vcpu, context, false); - update_last_pte_bitmap(vcpu, context); + update_last_nonleaf_level(vcpu, context); context->page_fault = paging32_page_fault; context->gva_to_gpa = paging32_gva_to_gpa; @@ -4022,7 +4024,7 @@ static void init_kvm_tdp_mmu(struct kvm_vcpu *vcpu) } update_permission_bitmask(vcpu, context, false); - update_last_pte_bitmap(vcpu, context); + update_last_nonleaf_level(vcpu, context); reset_tdp_shadow_zero_bits_mask(vcpu, context); } @@ -4128,7 +4130,7 @@ static void init_kvm_nested_mmu(struct kvm_vcpu *vcpu) } update_permission_bitmask(vcpu, g_context, false); - update_last_pte_bitmap(vcpu, g_context); + update_last_nonleaf_level(vcpu, g_context); } static void init_kvm_mmu(struct kvm_vcpu *vcpu) -- 2.7.4