Commit b514c30f authored by Avi Kivity's avatar Avi Kivity
Browse files

KVM: MMU: Avoid access/dirty update loop if all is well 



Keep track of accessed/dirty bits; if they are all set, do not
enter the accessed/dirty update loop.

Reviewed-by: default avatarXiao Guangrong <xiaoguangrong@linux.vnet.ibm.com>
Signed-off-by: default avatarAvi Kivity <avi@redhat.com>
parent 71331a1d

arch/x86/kvm/paging_tmpl.h

+20 −6
Original line number Diff line number Diff line
@@ -151,7 +151,7 @@ static int FNAME(walk_addr_generic)(struct guest_walker *walker, 
	pt_element_t pte;

	pt_element_t __user *uninitialized_var(ptep_user);

	gfn_t table_gfn;

	unsigned index, pt_access, pte_access;

	unsigned index, pt_access, pte_access, accessed_dirty, shift;

	gpa_t pte_gpa;

	int offset;

	const int write_fault = access & PFERR_WRITE_MASK;
@@ -180,6 +180,7 @@ static int FNAME(walk_addr_generic)(struct guest_walker *walker, 
	ASSERT((!is_long_mode(vcpu) && is_pae(vcpu)) ||

	       (mmu->get_cr3(vcpu) & CR3_NONPAE_RESERVED_BITS) == 0);



	accessed_dirty = PT_ACCESSED_MASK;

	pt_access = pte_access = ACC_ALL;

	++walker->level;
@@ -224,6 +225,7 @@ static int FNAME(walk_addr_generic)(struct guest_walker *walker, 
			goto error;

		}



		accessed_dirty &= pte;

		pte_access = pt_access & gpte_access(vcpu, pte);



		walker->ptes[walker->level - 1] = pte;
@@ -251,11 +253,23 @@ static int FNAME(walk_addr_generic)(struct guest_walker *walker, 
	if (!write_fault)

		protect_clean_gpte(&pte_access, pte);



	/*

	 * On a write fault, fold the dirty bit into accessed_dirty by shifting it one

	 * place right.

	 *

	 * On a read fault, do nothing.

	 */

	shift = write_fault >> ilog2(PFERR_WRITE_MASK);

	shift *= PT_DIRTY_SHIFT - PT_ACCESSED_SHIFT;

	accessed_dirty &= pte >> shift;



	if (unlikely(!accessed_dirty)) {

		ret = FNAME(update_accessed_dirty_bits)(vcpu, mmu, walker, write_fault);

		if (unlikely(ret < 0))

			goto error;

		else if (ret)

			goto retry_walk;

	}



	walker->pt_access = pt_access;

	walker->pte_access = pte_access;