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SubjectRe: [RFC 29/33] KVM: VMX: Save instruction length on EPT violation
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On 08.11.23 17:15, Sean Christopherson wrote:
>
> On Wed, Nov 08, 2023, Alexander Graf wrote:
>> On 08.11.23 12:18, Nicolas Saenz Julienne wrote:
>>> Save the length of the instruction that triggered an EPT violation in
>>> struct kvm_vcpu_arch. This will be used to populate Hyper-V VSM memory
>>> intercept messages.
>>>
>>> Signed-off-by: Nicolas Saenz Julienne <nsaenz@amazon.com>
>>
>> In v1, please do this for SVM as well :)
> Why? KVM caches values on VMX because VMREAD is measurable slower than memory
> accesses, especially when running nested. SVM has no such problems. I wouldn't
> be surprised if adding a "cache" is actually less performant due to increased
> pressure and misses on the hardware cache.


My understanding was that this patch wasn't about caching it, it was
about storing it somewhere generically so we can use it for the fault
injection code path in the following patch. And if we don't set this
variable for SVM, it just means Credential Guard fault injection would
be broken there.


Alex




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