On Wed, 07 Sep 2022, Dan Williams wrote:

Davidlohr Bueso wrote:
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.

To be clear nfit stuff and CXL does run in guests, but they do not
support secure-erase in a guest.

Yes, I meant the feats this api enables.

However, the QEMU CXL enabling is building the ability to do *guest
physical* address space management, but in that case the driver can be
paravirtualized to realize that it is not managing host-physical address
space and does not need to flush caches. That will need some indicator
to differentiate virtual CXL memory expanders from assigned devices. Is
there such a thing as a PCIe-virtio extended capability to differentiate
physical vs emulated devices?

In any case such check would be specific to each user (cxl in this case),
and outside the scope of _this_ particular api. Here we just really want to
avoid the broken TDX guest bits.

Thanks,
Davidlohr

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