On 28/09/20 14:42, Kang, Luwei wrote:
>> No, if a feature cannot be emulated, that means it cannot be
>> enabled unless it matches the host. That's generally not a problem
>> since Intel PT is usually used only with "-cpu host".
>>
> The limitation of LIP in qemu will mask off the Intel PT in KVM guest
> even with "-cpu host". e.g. This bit will be set in SnowRidge HW and
> later.
I agree that QEMU would have to learn about LIP. Unlike this patch,
however, x86_cpu_filter_features would have to fail if host LIP != guest
LIP. That is, something like
(ecx_0 & INTEL_PT_IP_LIP)) !=
(env->features[INTEL_PT_ECX_0] & INTEL_PT_IP_LIP)
where "intel-pt-lip" would be a feature in env->features[INTEL_PT_ECX_0].
> How about "-cpu cpu_model, +intel-pt" use case? The current value of
> Intel PT CPUID is a constant. Can we make the ICX CPUID as basic
> inforation(LIP is 0) and using "+intel-pt-lip" to make Intel PT work
> on the CPU which LIP is 1 on the host? As you mentioned before, Intel
> PT cannot be enabled in guest unless it matches the host.
Yes, this would work.
Paolo
