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Subject[PATCH v2 10/16] KVM: MMU: fask check whether page is writable
Using bit 1 (PTE_LIST_WP_BIT) in rmap store the write-protect status
to avoid unnecessary shadow page walking

Signed-off-by: Xiao Guangrong <xiaoguangrong@linux.vnet.ibm.com>
---
arch/x86/kvm/mmu.c | 40 ++++++++++++++++++++++++++++++++++------
1 files changed, 34 insertions(+), 6 deletions(-)
diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
index 0c6e92d..8b71908 100644
--- a/arch/x86/kvm/mmu.c
+++ b/arch/x86/kvm/mmu.c
@@ -796,7 +796,9 @@ static int mapping_level(struct kvm_vcpu *vcpu, gfn_t large_gfn)
return level - 1;
}

-#define PTE_LIST_DESC (0x1ull)
+#define PTE_LIST_DESC_BIT 0
+#define PTE_LIST_WP_BIT 1
+#define PTE_LIST_DESC (1 << PTE_LIST_DESC_BIT)
#define PTE_LIST_FLAG_MASK (0x3ull)

static void
@@ -1067,6 +1069,12 @@ 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))
+ __test_and_set_bit(PTE_LIST_WP_BIT, rmapp);
+}
+
static int rmap_add(struct kvm_vcpu *vcpu, u64 *spte, gfn_t gfn)
{
struct kvm_mmu_page *sp;
@@ -1074,7 +1082,10 @@ 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);
}

@@ -1164,16 +1175,23 @@ static bool rmap_write_protect(struct kvm *kvm, u64 gfn)
{
struct kvm_memory_slot *slot;
unsigned long *rmapp;
- int i;
+ int i = PT_PAGE_TABLE_LEVEL;
bool write_protected = false;

slot = gfn_to_memslot(kvm, gfn);
+ rmapp = __gfn_to_rmap(gfn, i, slot);
+
+ if (__test_and_set_bit(PTE_LIST_WP_BIT, rmapp))
+ return false;
+
+ do {
+ write_protected |= __rmap_write_protect(kvm, rmapp, i++);
+
+ if (i >= PT_PAGE_TABLE_LEVEL + KVM_NR_PAGE_SIZES)
+ break;

- for (i = PT_PAGE_TABLE_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);
- }
+ } while (true);

return write_protected;
}
@@ -1225,6 +1243,7 @@ static int kvm_set_pte_rmapp(struct kvm *kvm, unsigned long *rmapp,

mmu_spte_clear_track_bits(sptep);
mmu_spte_set(sptep, new_spte);
+ host_page_write_protect(sptep, rmapp);
}
}

@@ -2291,9 +2310,15 @@ 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;

+ rmap = gfn_to_rmap(vcpu->kvm, gfn, PT_PAGE_TABLE_LEVEL);
+
if (!vcpu->kvm->arch.indirect_shadow_pages)
+ goto write_free;
+
+ if (!test_bit(PTE_LIST_WP_BIT, rmap))
return 0;

for_each_gfn_indirect_valid_sp(vcpu->kvm, s, gfn, node) {
@@ -2309,6 +2334,9 @@ static int mmu_need_write_protect(struct kvm_vcpu *vcpu, gfn_t gfn,
}
if (need_unsync)
kvm_unsync_pages(vcpu, gfn);
+
+write_free:
+ __clear_bit(PTE_LIST_WP_BIT, rmap);
return 0;
}

--
1.7.7.6


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