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KVM: x86/mmu: Handle no-slot faults at the beginning of kvm_faultin_pfn()

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Handle the "no memslot" case at the beginning of kvm_faultin_pfn(), just
after the private versus shared check, so that there's no need to
repeatedly query whether or not a slot exists.  This also makes it more
obvious that, except for private vs. shared attributes, the process of
faulting in a pfn simply doesn't apply to gfns without a slot.

Opportunistically stuff @fault's metadata in kvm_handle_noslot_fault() so
that it doesn't need to be duplicated in all paths that invoke
kvm_handle_noslot_fault(), and to minimize the probability of not stuffing
the right fields.

Leave the existing handle behind, but convert it to a WARN, to guard
against __kvm_faultin_pfn() unexpectedly nullifying fault->slot.

Cc: David Matlack <dmatlack@google.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>
Reviewed-by: Kai Huang <kai.huang@intel.com>
Message-ID: <20240228024147.41573-14-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Sean Christopherson 2024-02-27 18:41:44 -08:00 • committed by Paolo Bonzini
parent cd272fc439
commit f6adeae81f
1 changed files with 17 additions and 12 deletions
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29
arch/x86/kvm/mmu/mmu.c
View file

@ -3269,6 +3269,10 @@ static int kvm_handle_noslot_fault(struct kvm_vcpu *vcpu,
vcpu_cache_mmio_info(vcpu, gva, fault->gfn, vcpu_cache_mmio_info(vcpu, gva, fault->gfn,
access & shadow_mmio_access_mask); access & shadow_mmio_access_mask);
fault->slot = NULL;
fault->pfn = KVM_PFN_NOSLOT;
fault->map_writable = false;
/* /*
* If MMIO caching is disabled, emulate immediately without * If MMIO caching is disabled, emulate immediately without
* touching the shadow page tables as attempting to install an * touching the shadow page tables as attempting to install an
@ -4349,15 +4353,18 @@ static int kvm_faultin_pfn(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault,
return -EFAULT; return -EFAULT;
} }
if (unlikely(!slot))
return kvm_handle_noslot_fault(vcpu, fault, access);
/* /*
* Retry the page fault if the gfn hit a memslot that is being deleted * Retry the page fault if the gfn hit a memslot that is being deleted
* or moved. This ensures any existing SPTEs for the old memslot will * or moved. This ensures any existing SPTEs for the old memslot will
* be zapped before KVM inserts a new MMIO SPTE for the gfn. * be zapped before KVM inserts a new MMIO SPTE for the gfn.
*/ */
if (slot && (slot->flags & KVM_MEMSLOT_INVALID)) if (slot->flags & KVM_MEMSLOT_INVALID)
return RET_PF_RETRY; return RET_PF_RETRY;
if (slot && slot->id == APIC_ACCESS_PAGE_PRIVATE_MEMSLOT) { if (slot->id == APIC_ACCESS_PAGE_PRIVATE_MEMSLOT) {
/* /*
* Don't map L1's APIC access page into L2, KVM doesn't support * Don't map L1's APIC access page into L2, KVM doesn't support
* using APICv/AVIC to accelerate L2 accesses to L1's APIC, * using APICv/AVIC to accelerate L2 accesses to L1's APIC,
@ -4369,12 +4376,9 @@ static int kvm_faultin_pfn(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault,
* uses different roots for L1 vs. L2, i.e. there is no danger * uses different roots for L1 vs. L2, i.e. there is no danger
* of breaking APICv/AVIC for L1. * of breaking APICv/AVIC for L1.
*/ */
if (is_guest_mode(vcpu)) { if (is_guest_mode(vcpu))
fault->slot = NULL; return kvm_handle_noslot_fault(vcpu, fault, access);
fault->pfn = KVM_PFN_NOSLOT;
fault->map_writable = false;
goto faultin_done;
}
/* /*
* If the APIC access page exists but is disabled, go directly * If the APIC access page exists but is disabled, go directly
* to emulation without caching the MMIO access or creating a * to emulation without caching the MMIO access or creating a
@ -4385,6 +4389,9 @@ static int kvm_faultin_pfn(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault,
return RET_PF_EMULATE; return RET_PF_EMULATE;
} }
fault->mmu_seq = vcpu->kvm->mmu_invalidate_seq;
smp_rmb();
/* /*
* Check for a relevant mmu_notifier invalidation event before getting * Check for a relevant mmu_notifier invalidation event before getting
* the pfn from the primary MMU, and before acquiring mmu_lock. * the pfn from the primary MMU, and before acquiring mmu_lock.
@ -4406,19 +4413,17 @@ static int kvm_faultin_pfn(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault,
* *guaranteed* to need to retry, i.e. waiting until mmu_lock is held * *guaranteed* to need to retry, i.e. waiting until mmu_lock is held
* to detect retry guarantees the worst case latency for the vCPU. * to detect retry guarantees the worst case latency for the vCPU.
*/ */
if (fault->slot && if (mmu_invalidate_retry_gfn_unsafe(vcpu->kvm, fault->mmu_seq, fault->gfn))
mmu_invalidate_retry_gfn_unsafe(vcpu->kvm, fault->mmu_seq, fault->gfn))
return RET_PF_RETRY; return RET_PF_RETRY;
ret = __kvm_faultin_pfn(vcpu, fault); ret = __kvm_faultin_pfn(vcpu, fault);
if (ret != RET_PF_CONTINUE) if (ret != RET_PF_CONTINUE)
return ret; return ret;
faultin_done:
if (unlikely(is_error_pfn(fault->pfn))) if (unlikely(is_error_pfn(fault->pfn)))
return kvm_handle_error_pfn(vcpu, fault); return kvm_handle_error_pfn(vcpu, fault);
if (unlikely(!fault->slot)) if (WARN_ON_ONCE(!fault->slot))
return kvm_handle_noslot_fault(vcpu, fault, access); return kvm_handle_noslot_fault(vcpu, fault, access);
/* /*