Re: [PATCH 2/2] kvm/x86: move and fix substitue search for missing CPUID entries

[Avi Kivity <avi@redhat.com>]

On 03/31/2011 03:13 PM, Andre Przywara wrote:
> If KVM cannot find an exact match for a requested CPUID leaf, the
> code will try to find the closest match instead of simply confessing
> it's failure.
> The implementation was meant to satisfy the CPUID specification, but
> did not properly check for extended and standard leaves and also
> didn't account for the index subleaf.
> Beside that this rule only applies to CPUID intercepts, which is not
> the only user of the kvm_find_cpuid_entry() function.
>
> So fix this algorithm and move it into kvm_emulate_cpuid().
> This fixes a crash of newer Linux kernels as KVM guests on
> AMD Bulldozer CPUs, where bogus values were returned in response to
> a CPUID intercept.
>
> @@ -4996,6 +4990,19 @@ void kvm_emulate_cpuid(struct kvm_vcpu *vcpu)
>   	kvm_register_write(vcpu, VCPU_REGS_RCX, 0);
>   	kvm_register_write(vcpu, VCPU_REGS_RDX, 0);
>   	best = kvm_find_cpuid_entry(vcpu, function, index);
> +
> +	/* if no match is found, check whether we exceed the vCPU's limit
> +	 * and return the content of the highest valid standard leaf instead.
> +	 * This is to satisfy the CPUID specification.
> +	 */
> +	if (!best) {
> +		best = kvm_find_cpuid_entry(vcpu, function&  0x80000000, 0);

"highest valid standard leaf" means the second argument should be zero, no?

> +		if (best&&  best->eax<  function)
> +			best = kvm_find_cpuid_entry(vcpu, best->eax, index);
> +		else
> +			best = NULL;
> +	}
> +
>   	if (best) {
>   		kvm_register_write(vcpu, VCPU_REGS_RAX, best->eax);
>   		kvm_register_write(vcpu, VCPU_REGS_RBX, best->ebx);


-- 
error compiling committee.c: too many arguments to function

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