Make all sptes to be writable if the gfn become write-free to reduce
the later page fault
The idea is from Avi
Signed-off-by: Xiao Guangrong <xiaoguangrong@xxxxxxxxxxxxxxxxxx>
---
arch/x86/kvm/mmu.c | 34 +++++++++++++++++++++++++++++++++-
1 files changed, 33 insertions(+), 1 deletions(-)
diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
index 578a1e2..efa5d59 100644
--- a/arch/x86/kvm/mmu.c
+++ b/arch/x86/kvm/mmu.c
@@ -2323,15 +2323,45 @@ static void kvm_unsync_pages(struct kvm_vcpu *vcpu, gfn_t gfn)
}
}
+/*
+ * If the gfn become write-free, we make all sptes which point to this
+ * gfn to be writable.
+ * Note: we should call mark_page_dirty for the gfn later.
+ */
+static void rmap_break_page_table_wp(struct kvm_memory_slot *slot, gfn_t gfn)
+{
+ struct spte_iterator iter;
+ u64 *sptep;
+ int i;
+
+ for (i = PT_PAGE_TABLE_LEVEL;
+ i < PT_PAGE_TABLE_LEVEL + KVM_NR_PAGE_SIZES; i++) {
+ unsigned long *rmap = __gfn_to_rmap(gfn, i, slot);
+
+ for_each_rmap_spte(rmap, &iter, sptep) {
+ u64 spte = *sptep;
+
+ if (!is_writable_pte(spte) &&
+ (spte & SPTE_ALLOW_WRITE)) {
+ spte &= ~SPTE_WRITE_PROTECT;
+ spte |= PT_WRITABLE_MASK;
+ mmu_spte_update(sptep, spte);
+ }
+ }
+ }
+}
+
static int mmu_need_write_protect(struct kvm_vcpu *vcpu, gfn_t gfn,
bool can_unsync)
{
+ struct kvm_memory_slot *slot;
struct kvm_mmu_page *s;
struct hlist_node *node;
unsigned long *rmap;
bool need_unsync = false;
- rmap = gfn_to_rmap(vcpu->kvm, gfn, PT_PAGE_TABLE_LEVEL);
+ slot = gfn_to_memslot(vcpu->kvm, gfn);
+ rmap = __gfn_to_rmap(gfn, PT_PAGE_TABLE_LEVEL, slot);
if (!vcpu->kvm->arch.indirect_shadow_pages)
goto write_free;
@@ -2353,6 +2383,8 @@ static int mmu_need_write_protect(struct kvm_vcpu *vcpu, gfn_t gfn,
if (need_unsync)
kvm_unsync_pages(vcpu, gfn);
+ rmap_break_page_table_wp(slot, gfn);
+
write_free:
__clear_bit(PTE_LIST_WP_BIT, rmap);
return 0;
--
1.7.7.6
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