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[70.53.122.15]) by smtp.gmail.com with ESMTPSA id s20sm3111044qtj.63.2020.08.24.08.43.56 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 24 Aug 2020 08:43:56 -0700 (PDT) Date: Mon, 24 Aug 2020 11:43:59 -0400 From: Peter Xu To: Alistair Popple Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, Andrew Morton , =?utf-8?B?SsOpcsO0bWU=?= Glisse , John Hubbard , Ralph Campbell , stable@vger.kernel.org Subject: Re: [PATCH 2/2] mm/rmap: Fixup copying of soft dirty and uffd ptes Message-ID: <20200824154359.GA8605@xz-x1> References: <20200824083128.12684-1-alistair@popple.id.au> <20200824083128.12684-2-alistair@popple.id.au> MIME-Version: 1.0 In-Reply-To: <20200824083128.12684-2-alistair@popple.id.au> Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=peterx@redhat.com X-Mimecast-Spam-Score: 0.002 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Disposition: inline X-Rspamd-Queue-Id: B9BA56C04 X-Spamd-Result: default: False [0.00 / 100.00] X-Rspamd-Server: rspam05 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Mon, Aug 24, 2020 at 06:31:28PM +1000, Alistair Popple wrote: > During memory migration a pte is temporarily replaced with a migration > swap pte. Some pte bits from the existing mapping such as the soft-dirty > and uffd write-protect bits are preserved by copying these to the > temporary migration swap pte. > > However these bits are not stored at the same location for swap and > non-swap ptes. Therefore testing these bits requires using the > appropriate helper function for the given pte type. > > Unfortunately several code locations were found where the wrong helper > function is being used to test soft_dirty and uffd_wp bits which leads > to them getting incorrectly set or cleared during page-migration. > > Fix these by using the correct tests based on pte type. > > Fixes: a5430dda8a3a ("mm/migrate: support un-addressable ZONE_DEVICE page in migration") > Fixes: 8c3328f1f36a ("mm/migrate: migrate_vma() unmap page from vma while collecting pages") > Fixes: f45ec5ff16a7 ("userfaultfd: wp: support swap and page migration") > Signed-off-by: Alistair Popple > Cc: stable@vger.kernel.org > --- > mm/migrate.c | 6 ++++-- > mm/rmap.c | 9 +++++++-- > 2 files changed, 11 insertions(+), 4 deletions(-) > > diff --git a/mm/migrate.c b/mm/migrate.c > index ddb64253fe3e..5bea19c496af 100644 > --- 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 } ? Thanks, -- Peter Xu