Re: [PATCH -next] memregion: Add arch_flush_memregion() interface

[Davidlohr Bueso <dave@stgolabs.net>]

On Wed, 07 Sep 2022, Borislav Petkov wrote:

>On Mon, Aug 29, 2022 at 02:29:18PM -0700, Davidlohr Bueso wrote:
>> diff --git a/arch/x86/mm/pat/set_memory.c b/arch/x86/mm/pat/set_memory.c
>> index 1abd5438f126..18463cb704fb 100644
>> --- a/arch/x86/mm/pat/set_memory.c
>> +++ b/arch/x86/mm/pat/set_memory.c
>> @@ -330,6 +330,20 @@ void arch_invalidate_pmem(void *addr, size_t size)
>>  EXPORT_SYMBOL_GPL(arch_invalidate_pmem);
>>  #endif
>>
>> +#ifdef CONFIG_ARCH_HAS_MEMREGION_INVALIDATE
>> +bool arch_has_flush_memregion(void)
>> +{
>> +	return !cpu_feature_enabled(X86_FEATURE_HYPERVISOR);
>
>This looks really weird. Why does this need to care about HV at all?

So the context here is:

e2efb6359e62 ("ACPICA: Avoid cache flush inside virtual machines")

>
>Does that nfit stuff even run in guests?

No, nor does cxl. This was mostly in general a precautionary check such
that the api is unavailable in VMs.

>
>> +EXPORT_SYMBOL(arch_has_flush_memregion);
>
>...
>
>> +EXPORT_SYMBOL(arch_flush_memregion);
>
>Why aren't those exports _GPL?

Fine by me.

Thanks,
Davidlohr