[PATCH v4 06/11] KVM: x86/mmu: Handle no-slot faults in kvm_faultin_pfn()

Sean Christopherson
2022-10-12T18:17:54Z

From: David Matlack <dmatlack@google.com>

Handle faults on GFNs that do not have a backing memslot in
kvm_faultin_pfn() and drop handle_abnormal_pfn(). This eliminates
duplicate code in the various page fault handlers.

Opportunistically tweak the comment about handling gfn > host.MAXPHYADDR
to reflect that the effect of returning RET_PF_EMULATE at that point is
to avoid creating an MMIO SPTE for such GFNs.

No functional change intended.

Signed-off-by: David Matlack <dmatlack@google.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>
---
arch/x86/kvm/mmu/mmu.c | 56 ++++++++++++++++++----------------
arch/x86/kvm/mmu/paging_tmpl.h | 6 +---
2 files changed, 31 insertions(+), 31 deletions(-)

diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index 07c3f83b3204..5710be4d328b 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -3175,28 +3175,32 @@ static int kvm_handle_error_pfn(struct kvm_page_fault *fault)
return -EFAULT;
}

-static int handle_abnormal_pfn(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault,
- unsigned int access)
+static int kvm_handle_noslot_fault(struct kvm_vcpu *vcpu,
+ struct kvm_page_fault *fault,
+ unsigned int access)
{
- if (unlikely(!fault->slot)) {
- gva_t gva = fault->is_tdp ? 0 : fault->addr;
+ gva_t gva = fault->is_tdp ? 0 : fault->addr;

- vcpu_cache_mmio_info(vcpu, gva, fault->gfn,
- access & shadow_mmio_access_mask);
- /*
- * If MMIO caching is disabled, emulate immediately without
- * touching the shadow page tables as attempting to install an
- * MMIO SPTE will just be an expensive nop. Do not cache MMIO
- * whose gfn is greater than host.MAXPHYADDR, any guest that
- * generates such gfns is running nested and is being tricked
- * by L0 userspace (you can observe gfn > L1.MAXPHYADDR if
- * and only if L1's MAXPHYADDR is inaccurate with respect to
- * the hardware's).
- */
- if (unlikely(!enable_mmio_caching) ||
- unlikely(fault->gfn > kvm_mmu_max_gfn()))
- return RET_PF_EMULATE;
- }
+ vcpu_cache_mmio_info(vcpu, gva, fault->gfn,
+ access & shadow_mmio_access_mask);
+
+ /*
+ * If MMIO caching is disabled, emulate immediately without
+ * touching the shadow page tables as attempting to install an
+ * MMIO SPTE will just be an expensive nop.
+ */
+ if (unlikely(!enable_mmio_caching))
+ return RET_PF_EMULATE;
+
+ /*
+ * Do not create an MMIO SPTE for a gfn greater than host.MAXPHYADDR,
+ * any guest that generates such gfns is running nested and is being
+ * tricked by L0 userspace (you can observe gfn > L1.MAXPHYADDR if and
+ * only if L1's MAXPHYADDR is inaccurate with respect to the
+ * hardware's).
+ */
+ if (unlikely(fault->gfn > kvm_mmu_max_gfn()))
+ return RET_PF_EMULATE;

return RET_PF_CONTINUE;
}
@@ -4197,7 +4201,8 @@ static int __kvm_faultin_pfn(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault
return RET_PF_CONTINUE;
}

-static int kvm_faultin_pfn(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault)
+static int kvm_faultin_pfn(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault,
+ unsigned int access)
{
int ret;

@@ -4211,6 +4216,9 @@ static int kvm_faultin_pfn(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault)
if (unlikely(is_error_pfn(fault->pfn)))
return kvm_handle_error_pfn(fault);

+ if (unlikely(!fault->slot))
+ return kvm_handle_noslot_fault(vcpu, fault, access);
+
return RET_PF_CONTINUE;
}

@@ -4261,11 +4269,7 @@ static int direct_page_fault(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault
if (r)
return r;

- r = kvm_faultin_pfn(vcpu, fault);
- if (r != RET_PF_CONTINUE)
- return r;
-
- r = handle_abnormal_pfn(vcpu, fault, ACC_ALL);
+ r = kvm_faultin_pfn(vcpu, fault, ACC_ALL);
if (r != RET_PF_CONTINUE)
return r;

diff --git a/arch/x86/kvm/mmu/paging_tmpl.h b/arch/x86/kvm/mmu/paging_tmpl.h
index 30b9d9b6734f..60bd642bbb90 100644
--- a/arch/x86/kvm/mmu/paging_tmpl.h
+++ b/arch/x86/kvm/mmu/paging_tmpl.h
@@ -837,11 +837,7 @@ static int FNAME(page_fault)(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault
else
fault->max_level = walker.level;

- r = kvm_faultin_pfn(vcpu, fault);
- if (r != RET_PF_CONTINUE)
- return r;
-
- r = handle_abnormal_pfn(vcpu, fault, walker.pte_access);
+ r = kvm_faultin_pfn(vcpu, fault, walker.pte_access);
if (r != RET_PF_CONTINUE)
return r;