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Commit 5dc99b23 authored by Takuya Yoshikawa's avatar Takuya Yoshikawa Committed by Avi Kivity
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KVM: Avoid checking huge page mappings in get_dirty_log() 



Dropped such mappings when we enabled dirty logging and we will never
create new ones until we stop the logging.

For this we introduce a new function which can be used to write protect
a range of PT level pages: although we do not need to care about a range
of pages at this point, the following patch will need this feature to
optimize the write protection of many pages.

Signed-off-by: default avatarTakuya Yoshikawa <yoshikawa.takuya@oss.ntt.co.jp>
Signed-off-by: default avatarAvi Kivity <avi@redhat.com>
parent a0ed4607

arch/x86/include/asm/kvm_host.h

+3 −2
Original line number Diff line number Diff line
@@ -712,8 +712,9 @@ void kvm_mmu_set_mask_ptes(u64 user_mask, u64 accessed_mask, 


int kvm_mmu_reset_context(struct kvm_vcpu *vcpu);

void kvm_mmu_slot_remove_write_access(struct kvm *kvm, int slot);

int kvm_mmu_rmap_write_protect(struct kvm *kvm, u64 gfn,

			       struct kvm_memory_slot *slot);

void kvm_mmu_write_protect_pt_masked(struct kvm *kvm,

				     struct kvm_memory_slot *slot,

				     gfn_t gfn_offset, unsigned long mask);

void kvm_mmu_zap_all(struct kvm *kvm);

unsigned int kvm_mmu_calculate_mmu_pages(struct kvm *kvm);

void kvm_mmu_change_mmu_pages(struct kvm *kvm, unsigned int kvm_nr_mmu_pages);

arch/x86/kvm/mmu.c

+30 −10
Original line number Diff line number Diff line
@@ -1037,27 +1037,47 @@ static int __rmap_write_protect(struct kvm *kvm, unsigned long *rmapp, int level 
	return write_protected;

}



int kvm_mmu_rmap_write_protect(struct kvm *kvm, u64 gfn,

			       struct kvm_memory_slot *slot)

/**

 * kvm_mmu_write_protect_pt_masked - write protect selected PT level pages

 * @kvm: kvm instance

 * @slot: slot to protect

 * @gfn_offset: start of the BITS_PER_LONG pages we care about

 * @mask: indicates which pages we should protect

 *

 * Used when we do not need to care about huge page mappings: e.g. during dirty

 * logging we do not have any such mappings.

 */

void kvm_mmu_write_protect_pt_masked(struct kvm *kvm,

				     struct kvm_memory_slot *slot,

				     gfn_t gfn_offset, unsigned long mask)

{

	unsigned long *rmapp;

	int i, write_protected = 0;



	for (i = PT_PAGE_TABLE_LEVEL;

	     i < PT_PAGE_TABLE_LEVEL + KVM_NR_PAGE_SIZES; ++i) {

		rmapp = __gfn_to_rmap(gfn, i, slot);

		write_protected |= __rmap_write_protect(kvm, rmapp, i);

	}

	while (mask) {

		rmapp = &slot->rmap[gfn_offset + __ffs(mask)];

		__rmap_write_protect(kvm, rmapp, PT_PAGE_TABLE_LEVEL);



	return write_protected;

		/* clear the first set bit */

		mask &= mask - 1;

	}

}



static int rmap_write_protect(struct kvm *kvm, u64 gfn)

{

	struct kvm_memory_slot *slot;

	unsigned long *rmapp;

	int i;

	int write_protected = 0;



	slot = gfn_to_memslot(kvm, gfn);

	return kvm_mmu_rmap_write_protect(kvm, gfn, slot);



	for (i = PT_PAGE_TABLE_LEVEL;

	     i < PT_PAGE_TABLE_LEVEL + KVM_NR_PAGE_SIZES; ++i) {

		rmapp = __gfn_to_rmap(gfn, i, slot);

		write_protected |= __rmap_write_protect(kvm, rmapp, i);

	}



	return write_protected;

}



static int kvm_unmap_rmapp(struct kvm *kvm, unsigned long *rmapp,

arch/x86/kvm/x86.c

+3 −5
Original line number Diff line number Diff line
@@ -3095,13 +3095,11 @@ static void write_protect_slot(struct kvm *kvm, 


	/* Not many dirty pages compared to # of shadow pages. */

	if (nr_dirty_pages < kvm->arch.n_used_mmu_pages) {

		unsigned long gfn_offset;

		gfn_t offset;



		for_each_set_bit(gfn_offset, dirty_bitmap, memslot->npages) {

			unsigned long gfn = memslot->base_gfn + gfn_offset;

		for_each_set_bit(offset, dirty_bitmap, memslot->npages)

			kvm_mmu_write_protect_pt_masked(kvm, memslot, offset, 1);



			kvm_mmu_rmap_write_protect(kvm, gfn, memslot);

		}

		kvm_flush_remote_tlbs(kvm);

	} else

		kvm_mmu_slot_remove_write_access(kvm, memslot->id);