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authorAvi Kivity <avi@redhat.com>2012-09-16 14:03:02 +0200
committerAvi Kivity <avi@redhat.com>2012-09-20 12:00:09 +0200
commitb514c30f7729b66af481fde3c1225e832e339d5b (patch)
tree8d0744aa7f2fd57fd31e9aed72de177b74d7900d
parentKVM: MMU: Eliminate eperm temporary (diff)
downloadlinux-b514c30f7729b66af481fde3c1225e832e339d5b.tar.xz
linux-b514c30f7729b66af481fde3c1225e832e339d5b.zip
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: Xiao Guangrong <xiaoguangrong@linux.vnet.ibm.com> Signed-off-by: Avi Kivity <avi@redhat.com>
-rw-r--r--arch/x86/kvm/paging_tmpl.h26
1 files changed, 20 insertions, 6 deletions
diff --git a/arch/x86/kvm/paging_tmpl.h b/arch/x86/kvm/paging_tmpl.h
index 95a64d1dccc7..810c1da2ee44 100644
--- a/arch/x86/kvm/paging_tmpl.h
+++ b/arch/x86/kvm/paging_tmpl.h
@@ -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;