Re: [RFC PATCH 16/17] x86/sev: Add a #HV exception handler

[Tianyu Lan]

Thanks for your review.

On 11/11/2022 4:38 AM, Kalra, Ashish wrote:
> > +    UNWIND_HINT_REGS
> > +
> > +    /* Update pt_regs */
> > +    movq    ORIG_RAX(%rsp), %rsi    /* get error code into 2nd 
> > argument*/
> > +    movq    $-1, ORIG_RAX(%rsp)    /* no syscall to restart */
> > +
> > +    movq    %rsp, %rdi        /* pt_regs pointer */
> > +    call    kernel_\cfunc
> > +
> > +    jmp    paranoid_exit
> > +
> > +.Lfrom_usermode_switch_stack_\@:
> > +    idtentry_body user_\cfunc, has_error_code=1
>
> #HV exception handler cannot/does not inject an error code, so shouldn't
> has_error_code == 0?

Nice catch. Will update in the next version.

> > +    irqentry_state_t irq_state;
> > +
> > +    if (unlikely(on_hv_fallback_stack(regs))) {
> > +            instrumentation_begin();
> > +            panic("Can't handle #HV exception from unsupported 
> > context\n");
> > +            instrumentation_end();
> > +    }
>
> HV fallback stack exists and is used if we couldn't switch to HV stack. 
> If we have to issue a panic() here, why don't we simply issue the 
> panic() in hv_switch_off_ist(), when we couldn't switch to HV stack ?

Yes, this is a good idea. Will update. Thanks.