On 30.01.25 10:51, Simona Vetter wrote:
On Wed, Jan 29, 2025 at 12:54:03PM +0100, David Hildenbrand wrote:
Let's do it just like mprotect write-upgrade or during NUMA-hinting
faults on PROT_NONE PTEs: detect if the PTE can be writable by using
can_change_pte_writable().
Set the PTE only dirty if the folio is dirty: we might not
necessarily have a write access, and setting the PTE writable doesn't
require setting the PTE dirty.
Not sure whether there's much difference in practice, since a device
exclusive access means a write, so the folio better be dirty (unless we
aborted halfway through). But then I couldn't find the code in nouveau to
do that, so now I'm confused.
That confused me as well. Requiring the PTE to be writable does not
imply that it is dirty.
So something must either set the PTE or the folio dirty.
( In practice, most anonymous folios are dirty most of the time ... )
If we assume that "device-exclusive entries" are always dirty, then it
doesn't make sense to set the folio dirty when creating device-exclusive
entries. We'd always have to set the PTE dirty when restoring the
exclusive pte.
--
Cheers,
David / dhildenb
