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Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , David Rientjes , Shakeel Butt , Andrew Morton , Jann Horn , Pedro Falcato , "Matthew Wilcox (Oracle)" , Jan Kara , Nhat Pham , Johannes Weiner , Zi Yan , Matthew Brost , Joshua Hahn , Byungchul Park , Gregory Price , Ying Huang , Alistair Popple , Usama Arif , Kairui Song , =?utf-8?B?SsOpcsO0bWU=?= Glisse , Kiryl Shutsemau , Yu-cheng Yu , Dave Hansen , Dennis Zhou , Tejun Heo , Christoph Lameter , Peng Fan , Josef Bacik , Chris Mason , linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, "Borislav Petkov (AMD)" , Mark Brown , "Dennis Zhou (Facebook)" , Rick Edgecombe , stable@vger.kernel.org Subject: Re: [PATCH 08/13] mm/migrate_device: fix ksmd oops on a migrated KSM page Message-ID: References: <20261111-mason-migrate-et-al-fixes-v1-0-3d2454362e8d@kernel.org> <20261111-mason-migrate-et-al-fixes-v1-8-3d2454362e8d@kernel.org> Content-Type: text/plain; charset=us-ascii 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 di22DTtV 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A process that maps the page can also > loop in page faults when it next accesses the page. > > The problem arises because KSM doesn't know not to try to look at device > private memory that does not exist in the direct map. > > Disallow this from happening by explicitly testing for this scenario in > __migrate_device_pages(). > > Fixes: a5430dda8a3a ("mm/migrate: support un-addressable ZONE_DEVICE page in migration") > Cc: > Signed-off-by: Chris Mason > [ ljs: tweak commit message, comment ] > Signed-off-by: Lorenzo Stoakes (ARM) > --- > mm/migrate_device.c | 9 +++++++++ > 1 file changed, 9 insertions(+) > > diff --git a/mm/migrate_device.c b/mm/migrate_device.c > index 45e571dbfb4c..7ebd02ec303b 100644 > --- a/mm/migrate_device.c > +++ b/mm/migrate_device.c > @@ -1205,6 +1205,15 @@ static void __migrate_device_pages(unsigned long *src_pfns, > } > > > + /* > + * KSM doesn't know not to try to read device private pages, so > + * disallow the combination. > + */ > + if (folio_is_device_private(newfolio) && folio_test_ksm(folio)) { > + src_pfns[i] &= ~MIGRATE_PFN_MIGRATE; > + goto next; > + } > + > if (folio_is_device_private(newfolio) || > folio_is_device_coherent(newfolio)) { > if (mapping) { > Given that we don't move device private ksm folios, I guess the check in pin_anon_rmap() now applies only to device coherent folios. I agree with the comment earlier about detecting this condition earlier. Acked-by: Balbir Singh