Re: [PATCH v10 12/37] mm: use folio_zero_user for user pages in post_alloc_hook

[Gregory Price]

On Mon, Jun 08, 2026 at 12:23:07PM +0100, Lorenzo Stoakes wrote:
> On Mon, Jun 08, 2026 at 04:36:38AM -0400, Michael S. Tsirkin wrote:
> 
> > +			 * user_addr != USER_ADDR_NONE implies sleepable
> > +			 * context (user page fault).
> 
> Can you safely assume that? Also inferring which context we are in from this
> parameter seems risky.
> 
> It seems to me that you're now making it such that kernel developers:
> 
> - Have to know when and when not to specify a user address, and under what
>   circumstances we might consider that to be mapped.
> 
> - Need to know to do this correctly for aliasing architectures or have silent
>   correctness issues.
> 
> - Need to take context into account when specifying this.
> 
> We definitely need to find a simpler way to do this!
>

This feedback was poked at in earlier versions.  There's a tension
between keeping the old interface as-is, having explicit interfaces
for something like this, and the state of a page inside the
allocator vs outside.

Double-plus complicated by the fact that we're trying to reason about
two allocators at once:  host and guest.

It seems it has gotten a bit more complicated since then (I missed this
"sleepable context" bit, not sure if it was there on prior versions).

If `user_addr` is now implying anything other than exactly: "This needs
to be zeroed / caches flushed", then this is bad.

~Gregory