Re: [PATCH] x86/shadow: suppress trace_emul_write_val hook when !TRACEBUFFER

[Jan Beulich <jbeulich@xxxxxxxx>]

On 27.01.2026 14:27, Andrew Cooper wrote:
> On 27/01/2026 1:20 pm, Jan Beulich wrote:
>> The hook is never invoked in that case, and hence needlessly offers an
>> extra valid indirect call target. With the hook suppressed, no consumer
>> of the three local per-CPU variables exists either, so they're
>> suppressed as well.
>>
>> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
>>
>> --- a/xen/arch/x86/include/asm/paging.h
>> +++ b/xen/arch/x86/include/asm/paging.h
>> @@ -90,10 +90,12 @@ struct shadow_paging_mode {
>>      int           (*guess_wrmap           )(struct vcpu *v, 
>>                                              unsigned long vaddr, mfn_t 
>> gmfn);
>>      void          (*pagetable_dying       )(paddr_t gpa);
>> +#ifdef CONFIG_TRACEBUFFER
>>      void          (*trace_emul_write_val  )(const void *ptr, unsigned long 
>> vaddr,
>>                                              const void *src, unsigned int 
>> bytes);
>>  #endif
>>  #endif
>> +#endif
> 
> Can we get some comments on these endifs, and ...

I can touch the pre-existing ones here, but the new one spanning just two
lines here and ...

>> --- a/xen/arch/x86/mm/shadow/multi.c
>> +++ b/xen/arch/x86/mm/shadow/multi.c
>> @@ -4130,7 +4142,9 @@ const struct paging_mode sh_paging_mode
>>      .shadow.guess_wrmap            = sh_guess_wrmap,
>>  #endif
>>      .shadow.pagetable_dying        = sh_pagetable_dying,
>> +#ifdef CONFIG_TRACEBUFFER
>>      .shadow.trace_emul_write_val   = trace_emulate_write_val,
>> +#endif
>>  #endif /* CONFIG_HVM */
> 
> ... this one too.

... one line here I didn't think would need comments?

> Otherwise, Reviewed-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>

Thanks.

Jan