Re: [PATCH] [v2] x86/fpu: Delay instruction pointer fixup until after warning

[Chang S. Bae]

On 6/25/2025 6:01 AM, Dave Hansen wrote:
> Right now, if XRSTOR fails a console message like this is be printed:
>
> 	Bad FPU state detected at restore_fpregs_from_fpstate+0x9a/0x170, reinitializing FPU registers.
>
> However, the text location (...+0x9a in this case) is the instruction
> *AFTER* the XRSTOR. The highlighted instruction in the "Code:" dump
> also points one instruction late.
>
> The reason is that the "fixup" moves RIP up to pass the bad XRSTOR and
> keep on running after returning from the #GP handler. But it does this
> fixup before warning.
>
> The resulting warning output is nonsensical because it looks like the
> non-FPU-related instruction is #GP'ing.
>
> Do not fix up RIP until after printing the warning. Do this by using> the more generic and standard ex_handler_default().

Indeed, the fix looks obvious and correct.

Also, the trick you previously shared for reproducing the fault is very 
useful for testing cases like this.

I would be happy to provide my tag:
Reviewed-by: Chang S. Bae <chang.seok.bae@xxxxxxxxx>

Thanks,
Chang