Messages in this thread | | | Date | Mon, 31 Jul 2023 10:03:34 -0500 | Subject | Re: [Question] int3 instruction generates a #UD in SEV VM | From | Tom Lendacky <> |
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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[*]? > > : > > 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? > : > : 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?
Thanks, Tom
> > [*] https://lore.kernel.org/all/ZMFd5kkehlkIfnBA@google.com
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