Re: [PATCH Part2 v6 07/49] x86/sev: Invalid pages from direct map when adding it to RMP table

[Kalra, Ashish]

Hello Boris,

On 12/29/2022 11:09 AM, Borislav Petkov wrote:
> On Tue, Dec 27, 2022 at 03:49:39PM -0600, Kalra, Ashish wrote:
> > Milan onward,
>
> And before ML there's no SNP, right?

Yes, that's correct.

> > there is H/W support for coherency between mappings of the
> > same physical page with different encryption keys, so AFAIK, there should be
> > no need to flush during page state transitions, where we invoke these direct
> > map interface functions for re-mapping/invalidating pages.
>
> Yah, that rings a bell.
>
> In any case, the fact that flushing is not needed should be stated
> somewhere in text so that it is clear why.
>
> > I don't know if there is any other reason to flush after modifying
> > the direct map ?
>
> There's
>
>          /*
>           * No need to flush, when we did not set any of the caching
>           * attributes:
>           */
>          cache = !!pgprot2cachemode(mask_set);
>
>
> Does the above HW cover this case too?

Actually, as both set_memory_p() and set_memory_np() are only 
setting/clearing the _PAGE_PRESENT flag and not changing any of the page 
caching attributes so this flush won't be required anyway.

Thanks,
Ashish

> Thx.