Re: [PATCH] x86/fpu: Delay instruction pointer fixup until after after warning

On 6/18/25 12:51, Alison Schofield wrote:

...

Do not fix up RIP until after printing the warning.

How was this found and how is the change verified?

Good questions.

I found it from an Intel-internal bug report. It's not clear what's causing the underlying XRSTOR #GP. But I spent some time scratching my head about how RIP got pointing to the wrong place. I was blaming the simulator at first.

I validated the fix using the attached patch. It waits until there's a program named "dave" running, then corrupts the XSAVE buffer in a way that will cause XRSTOR to #GP, triggering the warning that was off by an instruction.