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 *different* 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 that the intercepted vCPU actually cached all of the information that is held in its VMCS. The sane way to do this is to snapshot *all* information on the intercepted vCPU, 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*.
