[PATCH 5/5] KVM: MMU: fast invalid all mmio sptes

Xiao Guangrong
2013-03-15T15:30:26Z

This patch tries to introduce a very simple and scale way to invalid all
mmio sptes - it need not walk any shadow pages and hold mmu-lock

KVM maintains a global mmio invalid generation-number which is stored in
kvm->arch.mmio_invalid_gen and every mmio spte stores the current global
generation-number into his available bits when it is created

When KVM need zap all mmio sptes, it just simply increase the global
generation-number. When guests do mmio access, KVM intercepts a MMIO #PF
then it walks the shadow page table and get the mmio spte. If the
generation-number on the spte does not equal the global generation-number,
it will go to the normal #PF handler to update the mmio spte

Since 19 bits are used to store generation-number on mmio spte, the
generation-number can be round after 33554432 times. It is large enough
for nearly all most cases, but making the code be more strong, we zap all
shadow pages when the number is round

Signed-off-by: Xiao Guangrong <xiaoguangrong@linux.vnet.ibm.com>
---
arch/x86/include/asm/kvm_host.h | 2 +
arch/x86/kvm/mmu.c | 61 +++++++++++++++++++++++++++++++++------
arch/x86/kvm/mmutrace.h | 17 +++++++++++
arch/x86/kvm/paging_tmpl.h | 7 +++-
arch/x86/kvm/vmx.c | 4 ++
arch/x86/kvm/x86.c | 6 +--
6 files changed, 82 insertions(+), 15 deletions(-)

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index ef7f4a5..572398e 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -529,6 +529,7 @@ struct kvm_arch {
unsigned int n_requested_mmu_pages;
unsigned int n_max_mmu_pages;
unsigned int indirect_shadow_pages;
+ unsigned int mmio_invalid_gen;
struct hlist_head mmu_page_hash[KVM_NUM_MMU_PAGES];
/*
* Hash table of struct kvm_mmu_page.
@@ -765,6 +766,7 @@ void kvm_mmu_slot_remove_write_access(struct kvm *kvm, int slot);
void kvm_mmu_write_protect_pt_masked(struct kvm *kvm,
struct kvm_memory_slot *slot,
gfn_t gfn_offset, unsigned long mask);
+void kvm_mmu_invalid_mmio_spte(struct kvm *kvm);
void kvm_mmu_zap_all(struct kvm *kvm);
unsigned int kvm_mmu_calculate_mmu_pages(struct kvm *kvm);
void kvm_mmu_change_mmu_pages(struct kvm *kvm, unsigned int kvm_nr_mmu_pages);
diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
index 13626f4..7093a92 100644
--- a/arch/x86/kvm/mmu.c
+++ b/arch/x86/kvm/mmu.c
@@ -234,12 +234,13 @@ static unsigned int get_mmio_spte_generation(u64 spte)
static void mark_mmio_spte(struct kvm *kvm, u64 *sptep, u64 gfn,
unsigned access)
{
- u64 mask = generation_mmio_spte_mask(0);
+ unsigned int gen = ACCESS_ONCE(kvm->arch.mmio_invalid_gen);
+ u64 mask = generation_mmio_spte_mask(gen);

access &= ACC_WRITE_MASK | ACC_USER_MASK;
mask |= shadow_mmio_mask | access | gfn << PAGE_SHIFT;

- trace_mark_mmio_spte(sptep, gfn, access, 0);
+ trace_mark_mmio_spte(sptep, gfn, access, gen);
mmu_spte_set(sptep, mask);
}

@@ -269,6 +270,34 @@ static bool set_mmio_spte(struct kvm *kvm, u64 *sptep, gfn_t gfn,
return false;
}

+static bool check_mmio_spte(struct kvm *kvm, u64 spte)
+{
+ return get_mmio_spte_generation(spte) ==
+ ACCESS_ONCE(kvm->arch.mmio_invalid_gen);
+}
+
+/*
+ * The caller should protect concurrent access on
+ * kvm->arch.mmio_invalid_gen. Currently, it is used by
+ * kvm_arch_commit_memory_region and protected by kvm->slots_lock.
+ */
+void kvm_mmu_invalid_mmio_spte(struct kvm *kvm)
+{
+ /* Ensure update memslot has been completed. */
+ smp_mb();
+
+ trace_kvm_mmu_invalid_mmio_spte(kvm);
+
+ /*
+ * The very rare case: if the generation-number is round,
+ * zap all shadow pages.
+ */
+ if (unlikely(kvm->arch.mmio_invalid_gen++ == MAX_GEN)) {
+ kvm->arch.mmio_invalid_gen = 0;
+ return kvm_mmu_zap_all(kvm);
+ }
+}
+
static inline u64 rsvd_bits(int s, int e)
{
return ((1ULL << (e - s + 1)) - 1) << s;
@@ -3183,9 +3212,12 @@ static u64 walk_shadow_page_get_mmio_spte(struct kvm_vcpu *vcpu, u64 addr)
}

/*
- * If it is a real mmio page fault, return 1 and emulat the instruction
- * directly, return 0 to let CPU fault again on the address, -1 is
- * returned if bug is detected.
+ * Return value:
+ * 2: invalid spte is detected then let the real page fault path
+ * update the mmio spte.
+ * 1: it is a real mmio page fault, emulate the instruction directly.
+ * 0: let CPU fault again on the address.
+ * -1: bug is detected.
*/
int handle_mmio_page_fault_common(struct kvm_vcpu *vcpu, u64 addr, bool direct)
{
@@ -3200,6 +3232,9 @@ int handle_mmio_page_fault_common(struct kvm_vcpu *vcpu, u64 addr, bool direct)
gfn_t gfn = get_mmio_spte_gfn(spte);
unsigned access = get_mmio_spte_access(spte);

+ if (unlikely(!check_mmio_spte(vcpu->kvm, spte)))
+ return 2;
+
if (direct)
addr = 0;

@@ -3241,8 +3276,12 @@ static int nonpaging_page_fault(struct kvm_vcpu *vcpu, gva_t gva,

pgprintk("%s: gva %lx error %x\n", __func__, gva, error_code);

- if (unlikely(error_code & PFERR_RSVD_MASK))
- return handle_mmio_page_fault(vcpu, gva, error_code, true);
+ if (unlikely(error_code & PFERR_RSVD_MASK)) {
+ r = handle_mmio_page_fault(vcpu, gva, error_code, true);
+
+ if (likely(r != 2))
+ return r;
+ }

r = mmu_topup_memory_caches(vcpu);
if (r)
@@ -3318,8 +3357,12 @@ static int tdp_page_fault(struct kvm_vcpu *vcpu, gva_t gpa, u32 error_code,
ASSERT(vcpu);
ASSERT(VALID_PAGE(vcpu->arch.mmu.root_hpa));

- if (unlikely(error_code & PFERR_RSVD_MASK))
- return handle_mmio_page_fault(vcpu, gpa, error_code, true);
+ if (unlikely(error_code & PFERR_RSVD_MASK)) {
+ r = handle_mmio_page_fault(vcpu, gpa, error_code, true);
+
+ if (likely(r != 2))
+ return r;
+ }

r = mmu_topup_memory_caches(vcpu);
if (r)
diff --git a/arch/x86/kvm/mmutrace.h b/arch/x86/kvm/mmutrace.h
index f5b62a7..811254c 100644
--- a/arch/x86/kvm/mmutrace.h
+++ b/arch/x86/kvm/mmutrace.h
@@ -276,6 +276,23 @@ TRACE_EVENT(
__spte_satisfied(old_spte), __spte_satisfied(new_spte)
)
);
+
+TRACE_EVENT(
+ kvm_mmu_invalid_mmio_spte,
+ TP_PROTO(struct kvm *kvm),
+ TP_ARGS(kvm),
+
+ TP_STRUCT__entry(
+ __field(unsigned int, mmio_invalid_gen)
+ ),
+
+ TP_fast_assign(
+ __entry->mmio_invalid_gen = kvm->arch.mmio_invalid_gen;
+ ),
+
+ TP_printk("mmio_invalid_gen %x", __entry->mmio_invalid_gen
+ )
+);
#endif /* _TRACE_KVMMMU_H */

#undef TRACE_INCLUDE_PATH
diff --git a/arch/x86/kvm/paging_tmpl.h b/arch/x86/kvm/paging_tmpl.h
index 2c48e5f..c81f949 100644
--- a/arch/x86/kvm/paging_tmpl.h
+++ b/arch/x86/kvm/paging_tmpl.h
@@ -552,9 +552,12 @@ static int FNAME(page_fault)(struct kvm_vcpu *vcpu, gva_t addr, u32 error_code,

pgprintk("%s: addr %lx err %x\n", __func__, addr, error_code);

- if (unlikely(error_code & PFERR_RSVD_MASK))
- return handle_mmio_page_fault(vcpu, addr, error_code,
+ if (unlikely(error_code & PFERR_RSVD_MASK)) {
+ r = handle_mmio_page_fault(vcpu, addr, error_code,
mmu_is_nested(vcpu));
+ if (likely(r != 2))
+ return r;
+ };

r = mmu_topup_memory_caches(vcpu);
if (r)
diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index 54fdb76..ca8e9a3 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -5159,6 +5159,10 @@ static int handle_ept_misconfig(struct kvm_vcpu *vcpu)
if (likely(ret == 1))
return x86_emulate_instruction(vcpu, gpa, 0, NULL, 0) ==
EMULATE_DONE;
+
+ if (unlikely(ret == 2))
+ return kvm_mmu_page_fault(vcpu, gpa, 0, NULL, 0);
+
if (unlikely(!ret))
return 1;

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 81fb3c3..5b6d2a0 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -6996,10 +6996,8 @@ void kvm_arch_commit_memory_region(struct kvm *kvm,
* If memory slot is created, or moved, we need to clear all
* mmio sptes.
*/
- if ((change == KVM_MR_CREATE) || (change == KVM_MR_MOVE)) {
- kvm_mmu_zap_all(kvm);
- kvm_reload_remote_mmus(kvm);
- }
+ if ((change == KVM_MR_CREATE) || (change == KVM_MR_MOVE))
+ kvm_mmu_invalid_mmio_spte(kvm);
}

void kvm_arch_flush_shadow_all(struct kvm *kvm)
--
1.7.7.6