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KVM: MMU: simplify last_pte_bitmap

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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 <pbonzini@redhat.com>
This commit is contained in:
Paolo Bonzini 2016-02-23 12:51:19 +01:00
parent 50c9e6f3a6
commit 6bb69c9b69
2 changed files with 27 additions and 29 deletions
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8
arch/x86/include/asm/kvm_host.h
View File

@ -347,12 +347,8 @@ struct kvm_mmu {
struct rsvd_bits_validate guest_rsvd_check; struct rsvd_bits_validate guest_rsvd_check;
/* /* Can have large pages at levels 2..last_nonleaf_level-1. */
* Bitmap: bit set = last pte in walk u8 last_nonleaf_level;
* index[0:1]: level (zero-based)
* index[2]: pte.ps
*/
u8 last_pte_bitmap;
bool nx; bool nx;

48
arch/x86/kvm/mmu.c
View File

@ -3632,13 +3632,24 @@ static bool sync_mmio_spte(struct kvm_vcpu *vcpu, u64 *sptep, gfn_t gfn,
return false; 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); * The RHS has bit 7 set iff level < mmu->last_nonleaf_level.
return mmu->last_pte_bitmap & (1 << index); * 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 */ #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 root_level = mmu->root_level;
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) mmu->last_nonleaf_level = root_level;
--root_level; if (root_level == PT32_ROOT_LEVEL && is_pse(vcpu))
/* PT_PAGE_TABLE_LEVEL always terminates */ mmu->last_nonleaf_level++;
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;
} }
static void paging64_init_context_common(struct kvm_vcpu *vcpu, 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); reset_rsvds_bits_mask(vcpu, context);
update_permission_bitmask(vcpu, context, false); update_permission_bitmask(vcpu, context, false);
update_last_pte_bitmap(vcpu, context); update_last_nonleaf_level(vcpu, context);
MMU_WARN_ON(!is_pae(vcpu)); MMU_WARN_ON(!is_pae(vcpu));
context->page_fault = paging64_page_fault; 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); reset_rsvds_bits_mask(vcpu, context);
update_permission_bitmask(vcpu, context, false); 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->page_fault = paging32_page_fault;
context->gva_to_gpa = paging32_gva_to_gpa; 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_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); 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_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) static void init_kvm_mmu(struct kvm_vcpu *vcpu)