The following events can lead to an incorrect KVM_EXIT_MMIO bubbling
up to userspace:
(1) Guest accesses gpa X without a memory slot. The gfn is cached in
struct kvm_vcpu_arch (mmio_gfn). On Intel EPT-enabled hosts, KVM sets
the SPTE write-execute-noread so that future accesses cause
EPT_MISCONFIGs.
(2) Host userspace creates a memory slot via KVM_SET_USER_MEMORY_REGION
covering the page just accessed.
(3) Guest attempts to read or write to gpa X again. On Intel, this
generates an EPT_MISCONFIG. The memory slot generation number that
was incremented in (2) would normally take care of this but we fast
path mmio faults through quickly_check_mmio_pf(), which only checks
the per-vcpu mmio cache. Since we hit the cache, KVM passes a
KVM_EXIT_MMIO up to userspace.
This patch fixes the issue by clearing the mmio cache in the
KVM_MR_CREATE code path.
- introduce KVM_REQ_CLEAR_MMIO_CACHE for clearing all vcpu mmio
caches.
- extend vcpu_clear_mmio_info to clear mmio_gfn in addition to
mmio_gva, since both can be used to fast path mmio faults.
- issue KVM_REQ_CLEAR_MMIO_CACHE during memslot creation to flush
the mmio cache.
- in mmu_sync_roots, unconditionally clear the mmio cache since
even direct_map (e.g. tdp) hosts use it.
Signed-off-by: David Matlack <dmatlack@xxxxxxxxxx>
---
arch/x86/kvm/mmu.c | 3 ++-
arch/x86/kvm/x86.c | 5 +++++
arch/x86/kvm/x86.h | 8 +++++---
include/linux/kvm_host.h | 2 ++
virt/kvm/kvm_main.c | 10 +++++-----
5 files changed, 19 insertions(+), 9 deletions(-)
diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
index 9314678..8d50b84 100644
--- a/arch/x86/kvm/mmu.c
+++ b/arch/x86/kvm/mmu.c
@@ -3157,13 +3157,14 @@ static void mmu_sync_roots(struct kvm_vcpu *vcpu)
int i;
struct kvm_mmu_page *sp;
+ vcpu_clear_mmio_info(vcpu, MMIO_GVA_ANY);
+
if (vcpu->arch.mmu.direct_map)
return;
if (!VALID_PAGE(vcpu->arch.mmu.root_hpa))
return;
- vcpu_clear_mmio_info(vcpu, ~0ul);
kvm_mmu_audit(vcpu, AUDIT_PRE_SYNC);
if (vcpu->arch.mmu.root_level == PT64_ROOT_LEVEL) {
hpa_t root = vcpu->arch.mmu.root_hpa;
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index ef432f8..05b5629 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -6001,6 +6001,9 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
kvm_deliver_pmi(vcpu);
if (kvm_check_request(KVM_REQ_SCAN_IOAPIC, vcpu))
vcpu_scan_ioapic(vcpu);
+
+ if (kvm_check_request(KVM_REQ_CLEAR_MMIO_CACHE, vcpu))
+ vcpu_clear_mmio_info(vcpu, MMIO_GVA_ANY);
}
if (kvm_check_request(KVM_REQ_EVENT, vcpu) || req_int_win) {
@@ -7281,6 +7284,8 @@ void kvm_arch_memslots_updated(struct kvm *kvm)
* mmio generation may have reached its maximum value.
*/
kvm_mmu_invalidate_mmio_sptes(kvm);
+
+ kvm_make_all_vcpus_request(kvm, KVM_REQ_CLEAR_MMIO_CACHE);
}
int kvm_arch_prepare_memory_region(struct kvm *kvm,
diff --git a/arch/x86/kvm/x86.h b/arch/x86/kvm/x86.h
index 8c97bac..41ef197 100644
--- a/arch/x86/kvm/x86.h
+++ b/arch/x86/kvm/x86.h
@@ -81,15 +81,17 @@ static inline void vcpu_cache_mmio_info(struct kvm_vcpu *vcpu,
}
/*
- * Clear the mmio cache info for the given gva,
- * specially, if gva is ~0ul, we clear all mmio cache info.
+ * Clear the mmio cache info for the given gva. If gva is MMIO_GVA_ANY,
+ * unconditionally clear the mmio cache.
*/
+#define MMIO_GVA_ANY (~0ul)
static inline void vcpu_clear_mmio_info(struct kvm_vcpu *vcpu, gva_t gva)
{
- if (gva != (~0ul) && vcpu->arch.mmio_gva != (gva & PAGE_MASK))
+ if (gva != MMIO_GVA_ANY && vcpu->arch.mmio_gva != (gva & PAGE_MASK))
return;
vcpu->arch.mmio_gva = 0;
+ vcpu->arch.mmio_gfn = 0;
}
static inline bool vcpu_match_mmio_gva(struct kvm_vcpu *vcpu, unsigned long gva)
diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index ec4e3bd..e4edaff 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -136,6 +136,7 @@ static inline bool is_error_page(struct page *page)
#define KVM_REQ_GLOBAL_CLOCK_UPDATE 22
#define KVM_REQ_ENABLE_IBS 23
#define KVM_REQ_DISABLE_IBS 24
+#define KVM_REQ_CLEAR_MMIO_CACHE 25
#define KVM_USERSPACE_IRQ_SOURCE_ID 0
#define KVM_IRQFD_RESAMPLE_IRQ_SOURCE_ID 1
@@ -591,6 +592,7 @@ void kvm_vcpu_on_spin(struct kvm_vcpu *vcpu);
void kvm_load_guest_fpu(struct kvm_vcpu *vcpu);
void kvm_put_guest_fpu(struct kvm_vcpu *vcpu);
+bool kvm_make_all_vcpus_request(struct kvm *kvm, unsigned int req);
void kvm_flush_remote_tlbs(struct kvm *kvm);
void kvm_reload_remote_mmus(struct kvm *kvm);
void kvm_make_mclock_inprogress_request(struct kvm *kvm);
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 4b6c01b..d09527a 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -152,7 +152,7 @@ static void ack_flush(void *_completed)
{
}
-static bool make_all_cpus_request(struct kvm *kvm, unsigned int req)
+bool kvm_make_all_vcpus_request(struct kvm *kvm, unsigned int req)
{
int i, cpu, me;
cpumask_var_t cpus;
@@ -189,7 +189,7 @@ void kvm_flush_remote_tlbs(struct kvm *kvm)
long dirty_count = kvm->tlbs_dirty;
smp_mb();
- if (make_all_cpus_request(kvm, KVM_REQ_TLB_FLUSH))
+ if (kvm_make_all_vcpus_request(kvm, KVM_REQ_TLB_FLUSH))
++kvm->stat.remote_tlb_flush;
cmpxchg(&kvm->tlbs_dirty, dirty_count, 0);
}
@@ -197,17 +197,17 @@ EXPORT_SYMBOL_GPL(kvm_flush_remote_tlbs);
void kvm_reload_remote_mmus(struct kvm *kvm)
{
- make_all_cpus_request(kvm, KVM_REQ_MMU_RELOAD);
+ kvm_make_all_vcpus_request(kvm, KVM_REQ_MMU_RELOAD);
}
void kvm_make_mclock_inprogress_request(struct kvm *kvm)
{
- make_all_cpus_request(kvm, KVM_REQ_MCLOCK_INPROGRESS);
+ kvm_make_all_vcpus_request(kvm, KVM_REQ_MCLOCK_INPROGRESS);
}
void kvm_make_scan_ioapic_request(struct kvm *kvm)
{
- make_all_cpus_request(kvm, KVM_REQ_SCAN_IOAPIC);
+ kvm_make_all_vcpus_request(kvm, KVM_REQ_SCAN_IOAPIC);
}
int kvm_vcpu_init(struct kvm_vcpu *vcpu, struct kvm *kvm, unsigned id)
--
2.0.0.526.g5318336
--
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