linux-kernel - Re: [PATCH -next] memregion: Add arch_flush

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Date:   Wed, 7 Sep 2022 09:22:45 -0700
From:   Davidlohr Bueso <dave@...olabs.net>
To:     Borislav Petkov <bp@...en8.de>
Cc:     dan.j.williams@...el.com, x86@...nel.org, nvdimm@...ts.linux.dev,
        linux-cxl@...r.kernel.org, peterz@...radead.org,
        akpm@...ux-foundation.org, dave.jiang@...el.com,
        Jonathan.Cameron@...wei.com, vishal.l.verma@...el.com,
        ira.weiny@...el.com, a.manzanares@...sung.com,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH -next] memregion: Add arch_flush_memregion() interface

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