Re: [PATCH v2 11/12] x86/paravirt: Don't use pv_ops vector for MSR access functions

["H. Peter Anvin" <hpa@xxxxxxxxx>]

On 2025-09-30 12:49, H. Peter Anvin wrote:
> 
> /* Xen code, stub sets CF = 1 on failure */
> 
>    0:   e8 xx xx xx xx          call   asm_xen_pv_wrmsr
>    5:   73 03                   jnc    0xa
>    7:   0f 0b                   ud2
>    9:   90                      nop
>    a:
> 
> The trap point even ends up in the same place! UD2 can be any 1-, 2-, or
> 3-byte trapping instruction.
> 

You can, of course, also simply have a conditional jump, at the expense of
making the whole alternative block one byte longer:

  0:   e8 xx xx xx xx          call   asm_xen_pv_wrmsr
  5:   0f 82 xx xx xx xx       jc     wrmsr_failed

        -hpa