[PATCH] KVM: x86/mmu: consider the hva in mmu_notifer retry

From: David Stevens
Date: Mon Jan 25 2021 - 01:46:45 EST

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From: David Stevens <stevensd@xxxxxxxxxxxx>

Use the range passed to mmu_notifer's invalidate_range_start to prevent
spurious page fault retries due to changes in unrelated host virtual
addresses. This has the secondary effect of greatly reducing the
likelihood of extreme latency when handing a page fault due to another
thread having been preempted while modifying host virtual addresses.

Signed-off-by: David Stevens <stevensd@xxxxxxxxxxxx>
---
arch/powerpc/kvm/book3s_64_mmu_hv.c | 2 +-
arch/powerpc/kvm/book3s_64_mmu_radix.c | 2 +-
arch/x86/kvm/mmu/mmu.c | 16 ++++++++++------
arch/x86/kvm/mmu/paging_tmpl.h | 7 ++++---
include/linux/kvm_host.h | 22 +++++++++++++++++++++-
virt/kvm/kvm_main.c | 22 ++++++++++++++++++----
6 files changed, 55 insertions(+), 16 deletions(-)

diff --git a/arch/powerpc/kvm/book3s_64_mmu_hv.c b/arch/powerpc/kvm/book3s_64_mmu_hv.c
index 38ea396a23d6..8e06cd3f759c 100644
--- a/arch/powerpc/kvm/book3s_64_mmu_hv.c
+++ b/arch/powerpc/kvm/book3s_64_mmu_hv.c
@@ -590,7 +590,7 @@ int kvmppc_book3s_hv_page_fault(struct kvm_vcpu *vcpu,
} else {
/* Call KVM generic code to do the slow-path check */
pfn = __gfn_to_pfn_memslot(memslot, gfn, false, NULL,
- writing, &write_ok);
+ writing, &write_ok, NULL);
if (is_error_noslot_pfn(pfn))
return -EFAULT;
page = NULL;
diff --git a/arch/powerpc/kvm/book3s_64_mmu_radix.c b/arch/powerpc/kvm/book3s_64_mmu_radix.c
index bb35490400e9..e603de7ade52 100644
--- a/arch/powerpc/kvm/book3s_64_mmu_radix.c
+++ b/arch/powerpc/kvm/book3s_64_mmu_radix.c
@@ -822,7 +822,7 @@ int kvmppc_book3s_instantiate_page(struct kvm_vcpu *vcpu,

/* Call KVM generic code to do the slow-path check */
pfn = __gfn_to_pfn_memslot(memslot, gfn, false, NULL,
- writing, upgrade_p);
+ writing, upgrade_p, NULL);
if (is_error_noslot_pfn(pfn))
return -EFAULT;
page = NULL;
diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index 6d16481aa29d..79166288ed03 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -3658,8 +3658,8 @@ static bool kvm_arch_setup_async_pf(struct kvm_vcpu *vcpu, gpa_t cr2_or_gpa,
}

static bool try_async_pf(struct kvm_vcpu *vcpu, bool prefault, gfn_t gfn,
- gpa_t cr2_or_gpa, kvm_pfn_t *pfn, bool write,
- bool *writable)
+ gpa_t cr2_or_gpa, kvm_pfn_t *pfn, hva_t *hva,
+ bool write, bool *writable)
{
struct kvm_memory_slot *slot = kvm_vcpu_gfn_to_memslot(vcpu, gfn);
bool async;
@@ -3672,7 +3672,8 @@ static bool try_async_pf(struct kvm_vcpu *vcpu, bool prefault, gfn_t gfn,
}

async = false;
- *pfn = __gfn_to_pfn_memslot(slot, gfn, false, &async, write, writable);
+ *pfn = __gfn_to_pfn_memslot(slot, gfn, false, &async,
+ write, writable, hva);
if (!async)
return false; /* *pfn has correct page already */

@@ -3686,7 +3687,8 @@ static bool try_async_pf(struct kvm_vcpu *vcpu, bool prefault, gfn_t gfn,
return true;
}

- *pfn = __gfn_to_pfn_memslot(slot, gfn, false, NULL, write, writable);
+ *pfn = __gfn_to_pfn_memslot(slot, gfn, false, NULL,
+ write, writable, hva);
return false;
}

@@ -3699,6 +3701,7 @@ static int direct_page_fault(struct kvm_vcpu *vcpu, gpa_t gpa, u32 error_code,
gfn_t gfn = gpa >> PAGE_SHIFT;
unsigned long mmu_seq;
kvm_pfn_t pfn;
+ hva_t hva;
int r;

if (page_fault_handle_page_track(vcpu, error_code, gfn))
@@ -3717,7 +3720,8 @@ static int direct_page_fault(struct kvm_vcpu *vcpu, gpa_t gpa, u32 error_code,
mmu_seq = vcpu->kvm->mmu_notifier_seq;
smp_rmb();

- if (try_async_pf(vcpu, prefault, gfn, gpa, &pfn, write, &map_writable))
+ if (try_async_pf(vcpu, prefault, gfn, gpa, &pfn, &hva,
+ write, &map_writable))
return RET_PF_RETRY;

if (handle_abnormal_pfn(vcpu, is_tdp ? 0 : gpa, gfn, pfn, ACC_ALL, &r))
@@ -3725,7 +3729,7 @@ static int direct_page_fault(struct kvm_vcpu *vcpu, gpa_t gpa, u32 error_code,

r = RET_PF_RETRY;
spin_lock(&vcpu->kvm->mmu_lock);
- if (mmu_notifier_retry(vcpu->kvm, mmu_seq))
+ if (mmu_notifier_retry_hva(vcpu->kvm, mmu_seq, hva))
goto out_unlock;
r = make_mmu_pages_available(vcpu);
if (r)
diff --git a/arch/x86/kvm/mmu/paging_tmpl.h b/arch/x86/kvm/mmu/paging_tmpl.h
index 50e268eb8e1a..3171784139a4 100644
--- a/arch/x86/kvm/mmu/paging_tmpl.h
+++ b/arch/x86/kvm/mmu/paging_tmpl.h
@@ -790,6 +790,7 @@ static int FNAME(page_fault)(struct kvm_vcpu *vcpu, gpa_t addr, u32 error_code,
struct guest_walker walker;
int r;
kvm_pfn_t pfn;
+ hva_t hva;
unsigned long mmu_seq;
bool map_writable, is_self_change_mapping;
int max_level;
@@ -840,8 +841,8 @@ static int FNAME(page_fault)(struct kvm_vcpu *vcpu, gpa_t addr, u32 error_code,
mmu_seq = vcpu->kvm->mmu_notifier_seq;
smp_rmb();

- if (try_async_pf(vcpu, prefault, walker.gfn, addr, &pfn, write_fault,
- &map_writable))
+ if (try_async_pf(vcpu, prefault, walker.gfn, addr, &pfn, &hva,
+ write_fault, &map_writable))
return RET_PF_RETRY;

if (handle_abnormal_pfn(vcpu, addr, walker.gfn, pfn, walker.pte_access, &r))
@@ -869,7 +870,7 @@ static int FNAME(page_fault)(struct kvm_vcpu *vcpu, gpa_t addr, u32 error_code,

r = RET_PF_RETRY;
spin_lock(&vcpu->kvm->mmu_lock);
- if (mmu_notifier_retry(vcpu->kvm, mmu_seq))
+ if (mmu_notifier_retry_hva(vcpu->kvm, mmu_seq, hva))
goto out_unlock;

kvm_mmu_audit(vcpu, AUDIT_PRE_PAGE_FAULT);
diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index f3b1013fb22c..b70097685249 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -502,6 +502,8 @@ struct kvm {
struct mmu_notifier mmu_notifier;
unsigned long mmu_notifier_seq;
long mmu_notifier_count;
+ unsigned long mmu_notifier_range_start;
+ unsigned long mmu_notifier_range_end;
#endif
long tlbs_dirty;
struct list_head devices;
@@ -729,7 +731,7 @@ kvm_pfn_t gfn_to_pfn_memslot(struct kvm_memory_slot *slot, gfn_t gfn);
kvm_pfn_t gfn_to_pfn_memslot_atomic(struct kvm_memory_slot *slot, gfn_t gfn);
kvm_pfn_t __gfn_to_pfn_memslot(struct kvm_memory_slot *slot, gfn_t gfn,
bool atomic, bool *async, bool write_fault,
- bool *writable);
+ bool *writable, hva_t *hva);

void kvm_release_pfn_clean(kvm_pfn_t pfn);
void kvm_release_pfn_dirty(kvm_pfn_t pfn);
@@ -1203,6 +1205,24 @@ static inline int mmu_notifier_retry(struct kvm *kvm, unsigned long mmu_seq)
return 1;
return 0;
}
+
+static inline int mmu_notifier_retry_hva(struct kvm *kvm,
+ unsigned long mmu_seq,
+ unsigned long hva)
+{
+ /*
+ * Unlike mmu_notifier_retry, this function relies on
+ * kvm->mmu_lock for consistency.
+ */
+ if (unlikely(kvm->mmu_notifier_count)) {
+ if (kvm->mmu_notifier_range_start <= hva &&
+ hva < kvm->mmu_notifier_range_end)
+ return 1;
+ }
+ if (kvm->mmu_notifier_seq != mmu_seq)
+ return 1;
+ return 0;
+}
#endif

#ifdef CONFIG_HAVE_KVM_IRQ_ROUTING
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index fa9e3614d30e..d6e1ef5cb184 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -483,6 +483,18 @@ static int kvm_mmu_notifier_invalidate_range_start(struct mmu_notifier *mn,
* count is also read inside the mmu_lock critical section.
*/
kvm->mmu_notifier_count++;
+ if (likely(kvm->mmu_notifier_count == 1)) {
+ kvm->mmu_notifier_range_start = range->start;
+ kvm->mmu_notifier_range_end = range->end;
+ } else {
+ /**
+ * Tracking multiple concurrent ranges has diminishing returns,
+ * so just use the maximum range. This persists until after all
+ * outstanding invalidation operations complete.
+ */
+ kvm->mmu_notifier_range_start = 0;
+ kvm->mmu_notifier_range_end = ULONG_MAX;
+ }
need_tlb_flush = kvm_unmap_hva_range(kvm, range->start, range->end,
range->flags);
/* we've to flush the tlb before the pages can be freed */
@@ -2010,9 +2022,11 @@ static kvm_pfn_t hva_to_pfn(unsigned long addr, bool atomic, bool *async,

kvm_pfn_t __gfn_to_pfn_memslot(struct kvm_memory_slot *slot, gfn_t gfn,
bool atomic, bool *async, bool write_fault,
- bool *writable)
+ bool *writable, hva_t *hva)
{
unsigned long addr = __gfn_to_hva_many(slot, gfn, NULL, write_fault);
+ if (hva)
+ *hva = addr;

if (addr == KVM_HVA_ERR_RO_BAD) {
if (writable)
@@ -2041,19 +2055,19 @@ kvm_pfn_t gfn_to_pfn_prot(struct kvm *kvm, gfn_t gfn, bool write_fault,
bool *writable)
{
return __gfn_to_pfn_memslot(gfn_to_memslot(kvm, gfn), gfn, false, NULL,
- write_fault, writable);
+ write_fault, writable, NULL);
}
EXPORT_SYMBOL_GPL(gfn_to_pfn_prot);

kvm_pfn_t gfn_to_pfn_memslot(struct kvm_memory_slot *slot, gfn_t gfn)
{
- return __gfn_to_pfn_memslot(slot, gfn, false, NULL, true, NULL);
+ return __gfn_to_pfn_memslot(slot, gfn, false, NULL, true, NULL, NULL);
}
EXPORT_SYMBOL_GPL(gfn_to_pfn_memslot);

kvm_pfn_t gfn_to_pfn_memslot_atomic(struct kvm_memory_slot *slot, gfn_t gfn)
{
- return __gfn_to_pfn_memslot(slot, gfn, true, NULL, true, NULL);
+ return __gfn_to_pfn_memslot(slot, gfn, true, NULL, true, NULL, NULL);
}
EXPORT_SYMBOL_GPL(gfn_to_pfn_memslot_atomic);

--
2.30.0.280.ga3ce27912f-goog

Next message: Lai Jiangshan: "[PATCH V2] x86/entry/64: De-Xen-ify our NMI code further"
Previous message: Maulik Shah: "[PATCH v2 3/3] soc: qcom: rpmh: Conditionally check lockdep_assert_irqs_disabled()"
Next in thread: Sean Christopherson: "Re: [PATCH] KVM: x86/mmu: consider the hva in mmu_notifer retry"
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