From 0c7a98e34ddae6e45938f02d4ce7f04114ef0bdc Mon Sep 17 00:00:00 2001 From: Sean Christopherson Date: Fri, 6 Dec 2019 15:57:28 -0800 Subject: [PATCH] KVM: x86/mmu: WARN on an invalid root_hpa WARN on the existing invalid root_hpa checks in __direct_map() and FNAME(fetch). The "legitimate" path that invalidated root_hpa in the middle of a page fault is long since gone, i.e. it should no longer be impossible to invalidate in the middle of a page fault[*]. The root_hpa checks were added by two related commits 989c6b34f6a94 ("KVM: MMU: handle invalid root_hpa at __direct_map") 37f6a4e237303 ("KVM: x86: handle invalid root_hpa everywhere") to fix a bug where nested_vmx_vmexit() could be called *in the middle* of a page fault. At the time, vmx_interrupt_allowed(), which was and still is used by kvm_can_do_async_pf() via ->interrupt_allowed(), directly invoked nested_vmx_vmexit() to switch from L2 to L1 to emulate a VM-Exit on a pending interrupt. Emulating the nested VM-Exit resulted in root_hpa being invalidated by kvm_mmu_reset_context() without explicitly terminating the page fault. Now that root_hpa is checked for validity by kvm_mmu_page_fault(), WARN on an invalid root_hpa to detect any flows that reset the MMU while handling a page fault. The broken vmx_interrupt_allowed() behavior has long since been fixed and resetting the MMU during a page fault should not be considered legal behavior. [*] It's actually technically possible in FNAME(page_fault)() because it calls inject_page_fault() when the guest translation is invalid, but in that case the page fault handling is immediately terminated. Signed-off-by: Sean Christopherson Signed-off-by: Paolo Bonzini --- arch/x86/kvm/mmu/mmu.c | 2 +- arch/x86/kvm/mmu/paging_tmpl.h | 2 +- 2 files changed, 2 insertions(+), 2 deletions(-) diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c index bdba15ef88aa..51f81f10f9f7 100644 --- a/arch/x86/kvm/mmu/mmu.c +++ b/arch/x86/kvm/mmu/mmu.c @@ -3391,7 +3391,7 @@ static int __direct_map(struct kvm_vcpu *vcpu, gpa_t gpa, int write, gfn_t gfn = gpa >> PAGE_SHIFT; gfn_t base_gfn = gfn; - if (!VALID_PAGE(vcpu->arch.mmu->root_hpa)) + if (WARN_ON(!VALID_PAGE(vcpu->arch.mmu->root_hpa))) return RET_PF_RETRY; if (likely(max_level > PT_PAGE_TABLE_LEVEL)) diff --git a/arch/x86/kvm/mmu/paging_tmpl.h b/arch/x86/kvm/mmu/paging_tmpl.h index 3b0ba2a77e28..b53bed3c901c 100644 --- a/arch/x86/kvm/mmu/paging_tmpl.h +++ b/arch/x86/kvm/mmu/paging_tmpl.h @@ -637,7 +637,7 @@ static int FNAME(fetch)(struct kvm_vcpu *vcpu, gpa_t addr, if (FNAME(gpte_changed)(vcpu, gw, top_level)) goto out_gpte_changed; - if (!VALID_PAGE(vcpu->arch.mmu->root_hpa)) + if (WARN_ON(!VALID_PAGE(vcpu->arch.mmu->root_hpa))) goto out_gpte_changed; for (shadow_walk_init(&it, vcpu, addr); -- GitLab