linux-kernel - Re: [PATCH 2/2] mm/rmap: Fixup copying of soft dirty and uffd ptes

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Message-ID: <1650521.I2r5EI4MMx@cleo>
Date:   Tue, 25 Aug 2020 15:19:50 +1000
From:   Alistair Popple <alistair@...ple.id.au>
To:     Peter Xu <peterx@...hat.com>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        Jérôme Glisse <jglisse@...hat.com>,
        John Hubbard <jhubbard@...dia.com>,
        Ralph Campbell <rcampbell@...dia.com>, stable@...r.kernel.org
Subject: Re: [PATCH 2/2] mm/rmap: Fixup copying of soft dirty and uffd ptes

On Tuesday, 25 August 2020 1:43:59 AM AEST Peter Xu wrote:
> > --- a/mm/migrate.c
> > +++ b/mm/migrate.c
> > @@ -2427,9 +2427,11 @@ static int migrate_vma_collect_pmd(pmd_t *pmdp,
> > 
> >  			entry = make_migration_entry(page, mpfn &
> >  			
> >  						     MIGRATE_PFN_WRITE);
> >  			
> >  			swp_pte = swp_entry_to_pte(entry);
> > 
> > -			if (pte_soft_dirty(pte))
> > +			if ((is_swap_pte(pte) && pte_swp_soft_dirty(pte))
> > +				|| (!is_swap_pte(pte) && pte_soft_dirty(pte)))
> > 
> >  				swp_pte = pte_swp_mksoft_dirty(swp_pte);
> > 
> > -			if (pte_uffd_wp(pte))
> > +			if ((is_swap_pte(pte) && pte_swp_uffd_wp(pte))
> > +				|| (!is_swap_pte(pte) && pte_uffd_wp(pte)))
> > 
> >  				swp_pte = pte_swp_mkuffd_wp(swp_pte);
> >  			
> >  			set_pte_at(mm, addr, ptep, swp_pte);
> 
> The worst case is we'll call is_swap_pte() four times for each entry. Also
> considering we know it's not a pte_none() when reach here, how about:
> 
>   if (pte_present(pte)) {
>     // pte handling of both soft dirty and uffd-wp
>   } else {
>     // swap handling of both soft dirty and uffd-wp
>   }
> 
> ?

Works for me, I'd missed we knew it was not a pte_none() so will respin. 
Thanks!

 - Alistair
 
> Thanks,