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@xxxxxxxxxx
