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Commit 6bb69c9b authored by Paolo Bonzini's avatar Paolo Bonzini
Browse files

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: default avatarPaolo Bonzini <pbonzini@redhat.com>
parent 50c9e6f3

arch/x86/include/asm/kvm_host.h

+2 −6
Original line number Diff line number Diff line
@@ -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;

arch/x86/kvm/mmu.c

+26 −24
Original line number Diff line number Diff line
@@ -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;



	/*

	 * 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;



	index = level - 1;

	index |= (gpte & PT_PAGE_SIZE_MASK) >> (PT_PAGE_SIZE_SHIFT - 2);

	return mmu->last_pte_bitmap & (1 << index);

	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 */

	unsigned root_level = mmu->root_level;



	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;

	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)