Prevent the stage-2 fault handler from faulting in pages when KVM_MEM_EXIT_ON_MISSING is set by allowing its __gfn_to_pfn_memslot() calls to check the memslot flag. To actually make that behavior useful, prepare a KVM_EXIT_MEMORY_FAULT when the stage-2 handler returns EFAULT, e.g. when it cannot resolve the pfn. With KVM_MEM_EXIT_ON_MISSING enabled this effects the delivery of stage-2 faults as vCPU exits, which userspace can attempt to resolve without terminating the guest. Delivering stage-2 faults to userspace in this way sidesteps the significant scalabiliy issues associated with using userfaultfd for the same purpose. Signed-off-by: Anish Moorthy <amoorthy@xxxxxxxxxx> --- Documentation/virt/kvm/api.rst | 2 +- arch/x86/kvm/Kconfig | 1 + arch/x86/kvm/mmu/mmu.c | 8 ++++++-- 3 files changed, 8 insertions(+), 3 deletions(-) diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst index bf7bc21d56ac..d52757f9e1cb 100644 --- a/Documentation/virt/kvm/api.rst +++ b/Documentation/virt/kvm/api.rst @@ -8052,7 +8052,7 @@ See KVM_EXIT_MEMORY_FAULT for more information. 7.35 KVM_CAP_EXIT_ON_MISSING ---------------------------- -:Architectures: None +:Architectures: x86 :Returns: Informational only, -EINVAL on direct KVM_ENABLE_CAP. The presence of this capability indicates that userspace may set the diff --git a/arch/x86/kvm/Kconfig b/arch/x86/kvm/Kconfig index d43efae05794..09224e306abf 100644 --- a/arch/x86/kvm/Kconfig +++ b/arch/x86/kvm/Kconfig @@ -44,6 +44,7 @@ config KVM select KVM_VFIO select HAVE_KVM_PM_NOTIFIER if PM select KVM_GENERIC_HARDWARE_ENABLING + select HAVE_KVM_EXIT_ON_MISSING help Support hosting fully virtualized guest machines using hardware virtualization extensions. You will need a fairly recent diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c index b89a9518f6de..26388e4f42df 100644 --- a/arch/x86/kvm/mmu/mmu.c +++ b/arch/x86/kvm/mmu/mmu.c @@ -3305,6 +3305,10 @@ static int kvm_handle_error_pfn(struct kvm_vcpu *vcpu, struct kvm_page_fault *fa return RET_PF_RETRY; } + WARN_ON_ONCE(fault->goal_level != PG_LEVEL_4K); + + kvm_prepare_memory_fault_exit(vcpu, gfn_to_gpa(fault->gfn), PAGE_SIZE, + fault->write, fault->exec, fault->is_private); return -EFAULT; } @@ -4371,7 +4375,7 @@ static int __kvm_faultin_pfn(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault async = false; fault->pfn = __gfn_to_pfn_memslot(slot, fault->gfn, false, false, &async, fault->write, &fault->map_writable, - false, &fault->hva); + true, &fault->hva); if (!async) return RET_PF_CONTINUE; /* *pfn has correct page already */ @@ -4393,7 +4397,7 @@ static int __kvm_faultin_pfn(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault */ fault->pfn = __gfn_to_pfn_memslot(slot, fault->gfn, false, true, NULL, fault->write, &fault->map_writable, - false, &fault->hva); + true, &fault->hva); return RET_PF_CONTINUE; } -- 2.44.0.rc0.258.g7320e95886-goog
