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:

quoted

Milan onward,

And before ML there's no SNP, right?

Yes, that's correct.

quoted

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.

quoted

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.