On 08/29/2011 01:24 PM, Jan Kiszka wrote:
>
> static int handle_apic_access(struct kvm_vcpu *vcpu)
> {
> + unsigned long exit_qualification = vmcs_readl(EXIT_QUALIFICATION);
> + int access_type, offset;
> +
> + access_type = (exit_qualification>> 12)& 0xf;
> + offset = exit_qualification& 0xfff;
> + /*
> + * Sane guest uses MOV instead of string operations to
> + * write EOI, with written value not cared. So make a
> + * short-circuit here by avoiding heavy instruction
> + * emulation.
> + */
Is there no cheap way to validate this assumption and fall back to the
slow path in case it doesn't apply? E.g. reading the first instruction
byte and matching it against a whitelist? Even if the ignored scenarios
are highly unlikely, I think we so far tried hard to provide both fast
and accurate results to the guest in all cases.
Just reading the first byte requires a guest page table walk. This is
probably the highest cost in emulation (which also requires a walk for
the data access).
--
error compiling committee.c: too many arguments to function
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