On 2023/7/31 23:03, Tom Lendacky wrote: > On 7/31/23 09:30, Sean Christopherson wrote: >> On Sat, Jul 29, 2023, wuzongyong wrote: >>> Hi, >>> I am writing a firmware in Rust to support SEV based on project td-shim[1]. >>> But when I create a SEV VM (just SEV, no SEV-ES and no SEV-SNP) with the firmware, >>> the linux kernel crashed because the int3 instruction in int3_selftest() cause a >>> #UD. >> >> ... >> >>> BTW, if a create a normal VM without SEV by qemu & OVMF, the int3 instruction always generates a >>> #BP. >>> So I am confused now about the behaviour of int3 instruction, could anyone help to explain the behaviour? >>> Any suggestion is appreciated! >> >> Have you tried my suggestions from the other thread[*]? Firstly, I'm sorry for sending muliple mails with the same content. I thought the mails I sent previously didn't be sent successfully. And let's talk the problem here. >> >> : > > I'm curious how this happend. I cannot find any condition that would >> : > > cause the int3 instruction generate a #UD according to the AMD's spec. >> : >> : One possibility is that the value from memory that gets executed diverges from the >> : value that is read out be the #UD handler, e.g. due to patching (doesn't seem to >> : be the case in this test), stale cache/tlb entries, etc. >> : >> : > > BTW, it worked nomarlly with qemu and ovmf. >> : > >> : > Does this happen every time you boot the guest with your firmware? What >> : > processor are you running on? >> : Yes, every time. The processor I used is EPYC 7T83. >> : And have you ruled out KVM as the culprit? I.e. verified that KVM is NOT injecting >> : a #UD. That obviously shouldn't happen, but it should be easy to check via KVM >> : tracepoints. > > I have a feeling that KVM is injecting the #UD, but it will take instrumenting KVM to see which path the #UD is being injected from. > > Wu Zongyo, can you add some instrumentation to figure that out if the trace points towards KVM injecting the #UD? Ok, I will try to do that. > > Thanks, > Tom > >> >> [*] https://lore.kernel.org/all/ZMFd5kkehlkIfnBA@xxxxxxxxxx
