[Nouveau] [PATCH 9/9] mm: remove the MIGRATE_PFN_WRITE flag

[Jerome Glisse]

On Tue, Jul 30, 2019 at 07:46:33AM +0200, Christoph Hellwig wrote:
> On Mon, Jul 29, 2019 at 07:30:44PM -0400, Jerome Glisse wrote:
> > On Mon, Jul 29, 2019 at 05:28:43PM +0300, Christoph Hellwig wrote:
> > > The MIGRATE_PFN_WRITE is only used locally in migrate_vma_collect_pmd,
> > > where it can be replaced with a simple boolean local variable.
> > > 
> > > Signed-off-by: Christoph Hellwig <hch at lst.de>
> > 
> > NAK that flag is useful, for instance a anonymous vma might have
> > some of its page read only even if the vma has write permission.
> > 
> > It seems that the code in nouveau is wrong (probably lost that
> > in various rebase/rework) as this flag should be use to decide
> > wether to map the device memory with write permission or not.
> > 
> > I am traveling right now, i will investigate what happened to
> > nouveau code.
> 
> We can add it back when needed pretty easily.  Much of this has bitrotted
> way to fast, and the pending ppc kvmhmm code doesn't need it either.

Not using is a serious bug, i will investigate this friday.

Cheers,
Jérôme