[PATCH 08/13] KVM: MMU: fask check whether page is writable

Xiao Guangrong
2012-03-29T09:25:25Z

Using PTE_LIST_WRITE_PROTECT bit in rmap store the write-protect status to
avoid unnecessary shadow page walking

Also if no shadow page is indirect, the page is write-free

Signed-off-by: Xiao Guangrong <xiaoguangrong@linux.vnet.ibm.com>
---
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 84b9775..3887a07 100644
--- a/arch/x86/kvm/mmu.c
+++ b/arch/x86/kvm/mmu.c
@@ -797,6 +797,7 @@ static int mapping_level(struct kvm_vcpu *vcpu, gfn_t large_gfn)
}

#define PTE_LIST_DESC (0x1ull)
+#define PTE_LIST_WRITE_PROTECT (0x2ull)
#define PTE_LIST_FLAG_MASK (0x3ull)

static void
@@ -1016,6 +1017,13 @@ static bool rmap_can_add(struct kvm_vcpu *vcpu)
return mmu_memory_cache_free_objects(cache);
}

+static void host_page_write_protect(u64 *spte, unsigned long *rmapp)
+{
+ if (!(*spte & SPTE_HOST_WRITEABLE) &&
+ !(*rmapp & PTE_LIST_WRITE_PROTECT))
+ *rmapp |= PTE_LIST_WRITE_PROTECT;
+}
+
static int rmap_add(struct kvm_vcpu *vcpu, u64 *spte, gfn_t gfn)
{
struct kvm_mmu_page *sp;
@@ -1023,7 +1031,10 @@ static int rmap_add(struct kvm_vcpu *vcpu, u64 *spte, gfn_t gfn)

sp = page_header(__pa(spte));
kvm_mmu_page_set_gfn(sp, spte - sp->spt, gfn);
+
rmapp = gfn_to_rmap(vcpu->kvm, gfn, sp->role.level);
+ host_page_write_protect(spte, rmapp);
+
return pte_list_add(vcpu, spte, rmapp);
}

@@ -1130,8 +1141,17 @@ static int rmap_write_protect(struct kvm *kvm, u64 gfn)
int write_protected = 0;

slot = gfn_to_memslot(kvm, gfn);
+ rmapp = __gfn_to_rmap(gfn, PT_PAGE_TABLE_LEVEL, slot);

- for (i = PT_PAGE_TABLE_LEVEL;
+ if (*rmapp & PTE_LIST_WRITE_PROTECT)
+ return 0;
+
+ *rmapp |= PTE_LIST_WRITE_PROTECT;
+
+ write_protected |= __rmap_write_protect(kvm, rmapp,
+ PT_PAGE_TABLE_LEVEL);
+
+ for (i = PT_DIRECTORY_LEVEL;
i < PT_PAGE_TABLE_LEVEL + KVM_NR_PAGE_SIZES; ++i) {
rmapp = __gfn_to_rmap(gfn, i, slot);
write_protected |= __rmap_write_protect(kvm, rmapp, i);
@@ -1180,6 +1200,7 @@ static int kvm_set_pte_rmapp(struct kvm *kvm, unsigned long *rmapp,
new_spte &= ~shadow_accessed_mask;
mmu_spte_clear_track_bits(spte);
mmu_spte_set(spte, new_spte);
+ host_page_write_protect(spte, rmapp);
spte = rmap_next(rmapp, spte);
}
}
@@ -2247,8 +2268,16 @@ static int mmu_need_write_protect(struct kvm_vcpu *vcpu, gfn_t gfn,
{
struct kvm_mmu_page *s;
struct hlist_node *node;
+ unsigned long *rmap;
bool need_unsync = false;

+ if (!vcpu->kvm->arch.indirect_shadow_pages)
+ return 0;
+
+ rmap = gfn_to_rmap(vcpu->kvm, gfn, PT_PAGE_TABLE_LEVEL);
+ if (!(*rmap & PTE_LIST_WRITE_PROTECT))
+ return 0;
+
for_each_gfn_indirect_valid_sp(vcpu->kvm, s, gfn, node) {
if (!can_unsync)
return 1;
@@ -2262,6 +2291,9 @@ static int mmu_need_write_protect(struct kvm_vcpu *vcpu, gfn_t gfn,
}
if (need_unsync)
kvm_unsync_pages(vcpu, gfn);
+
+ *rmap &= ~PTE_LIST_WRITE_PROTECT;
+
return 0;
}

--
1.7.7.6