On 08.11.23 18:20, Sean Christopherson wrote:
On Wed, Nov 08, 2023, 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.
This is silly and unnecessarily obfuscates *why* (as my response regarding SVM
shows), i.e. that this is "needed" becuase the value is consumed by a 
vCPU, not because of performance concerns.

It's also broken, AFAICT nothing prevents the intercepted vCPU from hitting a
different EPT violation before the target vCPU consumes exit_instruction_len.

Holy cow.  All of deliver_gpa_intercept() is wildly unsafe.  Aside from race
conditions, which in and of themselves are a non-starter, nothing guarantees 
the intercepted vCPU actually cached all of the information that is held in its 

The sane way to do this is to snapshot *all* information on the intercepted 
and then hand that off as a payload to the target vCPU.  That is, assuming the
cross-vCPU stuff is actually necessary.  At a glance, I don't see anything that
explains *why*.

Yup, I believe you repeated the comment I had on the function - and Nicolas already agreed :). This should go through user space which automatically means you need to bubble up all necessary trap data to user space on the faulting vCPU and then inject the full set of data into the receiving one.

My point with the comment on this patch was "Don't break AMD (or ancient VMX without instruction length decoding [Does that exist? I know SVM has old CPUs that don't do it]) please".


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