On 08/21/2012 05:57 AM, Xiao Guangrong wrote:
> 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@xxxxxxxxxxxxxxxxxx>
> ---
> arch/x86/kvm/x86.c | 12 +++++++++++-
> 1 files changed, 11 insertions(+), 1 deletions(-)
>
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index fb0d937..704680d 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -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;
> }
>
Good catch. Did this actually happen or did you find it by code inspection?
--
error compiling committee.c: too many arguments to function
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