Branch-free code is fun and everybody knows how much Avi loves it,
but is_last_gpte 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 <pbonzini@xxxxxxxxxx>
---
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 1c3e390993a2..d110dc44d6c2 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 fecc9c51d924..1dbef19867e4 100644
--- a/arch/x86/kvm/mmu.c
+++ b/arch/x86/kvm/mmu.c
@@ -3625,13 +3625,24 @@ 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 */
@@ -3903,22 +3914,13 @@ 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,
@@ -3930,7 +3932,7 @@ 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;
@@ -3957,7 +3959,7 @@ 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;
@@ -4015,7 +4017,7 @@ 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);
}
@@ -4121,7 +4123,7 @@ 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)
--
1.8.3.1
--
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