Re: [PATCH v2 3/7] x86/sev: add support for RMPOPT instruction

[Kalra, Ashish]

On 3/25/2026 7:40 PM, Andrew Cooper wrote:
> On 25/03/2026 9:53 pm, Kalra, Ashish wrote:
>> On 3/4/2026 9:56 AM, Andrew Cooper wrote:
>>> It should be:
>>>
>>> static inline bool __rmpopt(unsigned long addr, unsigned int fn)
>>> {
>>>     bool res;
>>>
>>>     asm volatile (".byte 0xf2, 0x0f, 0x01, 0xfc"
>>>                  : "=ccc" (res)
>>>                  : "a" (addr), "c" (fn));
>>>
>>>     return res;
>>> }
>>>
>> The above constraints to use on_each_cpu_mask() is forcing the use of:
>>
>> void rmpopt(void *val)
> 
> No.  You don't break your thin wrapper in order to force it into a
> wrong-shaped hole.
> 
> You need something like this:
> 
> void do_rmpopt_optimise(void *val)
> {
>     unsigned long addr = *(unsigned long *)val;
> 
>     WARN_ON_ONCE(__rmpopt(addr, OPTIMISE));
> }
> 
> to invoke the wrapper safely from the IPI.  That will at obvious when
> something wrong occurs.

This wrapper i can/will use, but doing a WARN_ON_ONCE() is probably avoidable as 
there will be ranges where RMPOPT will always fail, such as while checking 
the RMP table entries itself, so there is a good chance that we will always trigger
the WARN_ON_ONCE() on the memory range containing the RMP table.

Thanks,
Ashish

> 
> ~Andrew