On Mon, 4 Jan 2021 at 00:42, tedheadster <tedheadster@xxxxxxxxx> wrote:
>
> Paolo,
> I am doing regression testing on a first generation i486 and came up
> with a kernel crash because it incorrectly thinks the processor
> supports KVM features. Yes, we do still support the ancient i486.
>
> This processor does NOT have the cpuid instruction, and I believe
> testing for it returns -1 (not supported) in two's-compliment form.
>
> I think the -1 is not checked for, and this is causing
> kvm_arch_para_features() to think it _does_ support
> KVM_CPUID_FEATURES, causing it to later execute an invalid opcode
> (cpuid).
Please try the latest Linus tree or kvm/queue, it will not have this
issue since commit 64b38bd1906bb ("x86/kvm: do not setup pv tlb flush
when not paravirtualized").
Wanpeng
