Re: [PATCH v5 24/38] mm/vma: enforce that mm-managed mappings may not set VMA_IO_BIT

On Mon, Oct 12, 2026 at 08:51:10PM +0200, David Hildenbrand (Arm) wrote:

On 10/12/26 20:48, Lorenzo Stoakes (ARM) wrote:

quoted

On Mon, Oct 12, 2026 at 08:39:35PM +0200, David Hildenbrand (Arm) wrote:

quoted

On 10/12/26 20:35, Lorenzo Stoakes (ARM) wrote:

quoted

That gets removed.


I mean we do that in a subsequent commit, I think even the next one?



Yeah, but to do that the code would now be something like:

	vma_flags_t masked = flags;

	/*
	  * vma_flags_is_mm_managed() tests VMA_IO_BIT, which will be removed
	 * in the next commit.
	 */
	vma_flags_clear(&flags, VMA_IO_BIT);
	if (!vma_flags_is_mm_managed(masked)) {
		...
	}

Is that really worth it?

I don't think there's really too much confusion intra-patch about that is there?

I would do it as above (- the comment, as that is the next patch indeed) and
only remove the vma_flags_clear() in the next patch.

But in any case, you should spell out that this is only temporary in the patch
description :)

And then there's a 'masked' variable that is unused?

You need to have two vma_flags_t variables to be able both clear VMA_IO_BIT
and use vma_flags_is_mm_managed().

So the change would have to be

+ 	vma_flags_t masked = *flags;
+
+ 	vma_flags_clear(&flags, VMA_IO_BIT);
+ 	if (!vma_flags_is_mm_managed(&masked)) {
+ 		...
+ 	}

Then:

- 	vma_flags_t masked = *flags;
-
- 	vma_flags_clear(&flags, VMA_IO_BIT);
- 	if (!vma_flags_is_mm_managed(&masked)) {
+ 	if (!vma_flags_is_mm_managed(flags)) {
 		...
 	}

Which doesn't really seem worth it for somebody who is confused between two
patches mid-series.

But if you feel strongly I can make the change like that?

Whatever you prefer. Most important thing for me was finding it in the next
patch and being pleasantly surprised ;)

I'd rather not then!

It was always intended that way, this was all part of a careful dance to ensure
correct behaviour right up until the point where we enforce that VMA_IO_BIT is only set when appropriate.

I can update the commit message to reflect it.

--
Cheers, Lorenzo