Do not drop large spte until it can be insteaded by small pages so that
the guest can happliy read memory through it
The idea is from Avi:
| As I mentioned before, write-protecting a large spte is a good idea,
| since it moves some work from protect-time to fault-time, so it reduces
| jitter. This removes the need for the return value.
Signed-off-by: Xiao Guangrong <xiaoguangrong@xxxxxxxxxxxxxxxxxx>
---
arch/x86/kvm/mmu.c | 21 ++++++---------------
1 files changed, 6 insertions(+), 15 deletions(-)
diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
index 9f628f7..0f90269 100644
--- a/arch/x86/kvm/mmu.c
+++ b/arch/x86/kvm/mmu.c
@@ -1105,7 +1105,7 @@ static void drop_large_spte(struct kvm_vcpu *vcpu, u64 *sptep)
/*
* Write-protect on the specified @sptep, @pt_protect indicates whether
- * spte writ-protection is caused by protecting shadow page table.
+ * spte write-protection is caused by protecting shadow page table.
* @flush indicates whether tlb need be flushed.
*
* Note: write protection is difference between drity logging and spte
@@ -1114,31 +1114,23 @@ static void drop_large_spte(struct kvm_vcpu *vcpu, u64 *sptep)
* its dirty bitmap is properly set.
* - for spte protection, the spte can be writable only after unsync-ing
* shadow page.
- *
- * Return true if the spte is dropped.
*/
-static bool
+static void
spte_write_protect(struct kvm *kvm, u64 *sptep, bool *flush, bool pt_protect)
{
u64 spte = *sptep;
if (!is_writable_pte(spte) &&
!(pt_protect && spte_is_locklessly_modifiable(spte)))
- return false;
+ return;
rmap_printk("rmap_write_protect: spte %p %llx\n", sptep, *sptep);
- if (__drop_large_spte(kvm, sptep)) {
- *flush |= true;
- return true;
- }
-
if (pt_protect)
spte &= ~SPTE_MMU_WRITEABLE;
spte = spte & ~PT_WRITABLE_MASK;
*flush |= mmu_spte_update(sptep, spte);
- return false;
}
static bool __rmap_write_protect(struct kvm *kvm, unsigned long *rmapp,
@@ -1150,11 +1142,8 @@ static bool __rmap_write_protect(struct kvm *kvm, unsigned long *rmapp,
for (sptep = rmap_get_first(*rmapp, &iter); sptep;) {
BUG_ON(!(*sptep & PT_PRESENT_MASK));
- if (spte_write_protect(kvm, sptep, &flush, pt_protect)) {
- sptep = rmap_get_first(*rmapp, &iter);
- continue;
- }
+ spte_write_protect(kvm, sptep, &flush, pt_protect);
sptep = rmap_get_next(&iter);
}
@@ -2611,6 +2600,8 @@ static int __direct_map(struct kvm_vcpu *vcpu, gpa_t v, int write,
break;
}
+ drop_large_spte(vcpu, iterator.sptep);
+
if (!is_shadow_present_pte(*iterator.sptep)) {
u64 base_addr = iterator.addr;
--
1.7.7.6
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