Re: [PATCH v2] s390/mm: add missing secure storage access fixups for donated memory

[Heiko Carstens <hca@linux.ibm.com>]

On Wed, Mar 11, 2026 at 03:17:22PM +0100, Janosch Frank wrote:
> > > -		rc = arch_make_folio_accessible(folio);
> > > +		rc = uv_convert_from_secure(folio_to_phys(folio));
> > > +		if (!rc)
> > > +			clear_bit(PG_arch_1, &folio->flags.f);
> > >   		folio_put(folio);
> > 
> > Isn't the clear_bit() racy? That is: another CPU could make the page secure
> > again, set (the still set) PG_arch_1, and then clear_bit() removes the bit,
> > and we end up with a secure page where PG_arch_1 is not set?
> > Which in turn would arch_make_folio_accessible() al
> > 
> > Or is that not possible?
> > 
> > Just wondering, since __make_folio_secure() requires the folio to be locked
> > when setting PG_arch_1, while clearing happens unlocked. But chances are high
> > that I don't understand the code.
> > 
> 
> __make_folio_secure() checks the refcount and if the comments hold true, it
> should protect us from a flag being set as long as we have the extra
> reference which we should have gotten via folio_try_get().
> 
> It does not protect us from a double clear.

Ok, then it should work. Thanks for explaining!