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

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

Reviewed-by: Xiao Guangrong <xiaoguangrong@linux.vnet.ibm.com>
Signed-off-by: Avi Kivity <avi@redhat.com>
This commit is contained in:
Avi Kivity 2012-09-16 15:03:02 +03:00
parent 71331a1da1
commit b514c30f77
1 changed files with 20 additions and 6 deletions
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26
arch/x86/kvm/paging_tmpl.h
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@ -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 @@ retry_walk:
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 @@ retry_walk:
goto error;
}
accessed_dirty &= pte;
pte_access = pt_access & gpte_access(vcpu, pte);
walker->ptes[walker->level - 1] = pte;
@ -251,11 +253,23 @@ retry_walk:
if (!write_fault)
protect_clean_gpte(&pte_access, pte);
ret = FNAME(update_accessed_dirty_bits)(vcpu, mmu, walker, write_fault);
if (unlikely(ret < 0))
goto error;
else if (ret)
goto retry_walk;
/*
* 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;