KVM: x86: fix possible infinite loop caused by reexecute_instruction (8e3d9d06) · Commits · 戴 / test

Currently, we reexecute all unhandleable instructions if they do not access on the mmio, however, it can not work if host map the readonly memory to guest. If the instruction try to write this kind of memory, it will fault again when guest retry it, then we will goto a infinite loop: retry instruction -> write #PF -> emulation fail -> retry instruction -> ... Fix it by retrying the instruction only when it faults on the writable memory Signed-off-by:

Xiao Guangrong <xiaoguangrong@linux.vnet.ibm.com> Signed-off-by:

Avi Kivity <avi@redhat.com>

arch/x86/kvm/x86.c

+11 −1

Original line number	Diff line number	Diff line
		@@ -4473,6 +4473,7 @@ static int handle_emulation_failure(struct kvm_vcpu *vcpu)
		static bool reexecute_instruction(struct kvm_vcpu *vcpu, gva_t gva)
		{
		gpa_t gpa;
		pfn_t pfn;

		if (tdp_enabled)
		return false;
		@@ -4490,8 +4491,17 @@ static bool reexecute_instruction(struct kvm_vcpu *vcpu, gva_t gva)
		if (gpa == UNMAPPED_GVA)
		return true; /* let cpu generate fault */

		if (!kvm_is_error_hva(gfn_to_hva(vcpu->kvm, gpa >> PAGE_SHIFT)))
		/*
		* Do not retry the unhandleable instruction if it faults on the
		* readonly host memory, otherwise it will goto a infinite loop:
		* retry instruction -> write #PF -> emulation fail -> retry
		* instruction -> ...
		*/
		pfn = gfn_to_pfn(vcpu->kvm, gpa_to_gfn(gpa));
		if (!is_error_pfn(pfn)) {
		kvm_release_pfn_clean(pfn);
		return true;
		}

		return false;
		}

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