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b=claYiCGD9+iGsb3rEHrI1s5HJg2hkS7W6gL8omu35jx7x6oqejSN3G4l7/5wm7Oj8 +qeUOcSoyvFJPDTJquyp36FHneu5xD9PqAyLHKJcQ+P3eTzJg10elubGWbYbJr+tvk gEE7trLBICmQyG4GF4bSPPqOoz8r1KexO9NQFWpt3u0Qf8T4/i/JJfkd3SpHnFKz99 RX6qVFtcgpOs+c+omD5H0aJsah5hYR2/8Ml0K83F+CITI6tNy81EbWhYtG4d4EAkVL yNTim2+Lm0L3zEKKV5p6v+OojCOKZ+TZsWnkiFcAAN0kVhGppFbuEVQCf5lkvEZkm2 Ixf8nfTRbGYxw== Message-ID: <38a23f8c-56c4-43a2-a3ed-bf7d4f784cda@kernel.org> Date: Thu, 2 Jul 2026 17:34:56 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 3/6] mm/rmap: use huge_ptep_get() in try_to_migrate_one() To: Dev Jain , muchun.song@linux.dev, osalvador@suse.de, akpm@linux-foundation.org, ljs@kernel.org, liam@infradead.org Cc: riel@surriel.com, vbabka@kernel.org, harry@kernel.org, jannh@google.com, lance.yang@linux.dev, kas@kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, rcampbell@nvidia.com, apopple@nvidia.com, ziy@nvidia.com, matthew.brost@intel.com, joshua.hahnjy@gmail.com, rakie.kim@sk.com, byungchul@sk.com, gourry@gourry.net, ying.huang@linux.alibaba.com, j-nomura@ce.jp.nec.com, nao.horiguchi@gmail.com, ak@linux.intel.com, mel@csn.ul.ie, pfalcato@suse.de, jpoimboe@kernel.org, dave.hansen@intel.com, tglx@kernel.org, catalin.marinas@arm.com, will@kernel.org, linux-arm-kernel@lists.infradead.org, ryan.roberts@arm.com, anshuman.khandual@arm.com, stable@vger.kernel.org References: <20260702051341.126509-1-dev.jain@arm.com> <20260702051341.126509-4-dev.jain@arm.com> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: ADF7BC0009 X-Stat-Signature: q8ofcuyc8oh5bcapn1g7kkh8kg6pfzw5 X-HE-Tag: 1783006507-247984 X-HE-Meta: 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 N/8Chm6D AD7LlEK1gC0GDMVzoXfGNyJTzeVTOI30hHxxnvmefJsBdSTIlXtyvFM4uc4q9TAWRnI0Ut9BgWRTGZzCMHsj/AB4nyC0trHMWQk1nQ8NdoIyepRd89X3WRYOtqKNnPy9+Un899sF3iEvL05jYdWryf6dgpqnXiotSw6nFxn/tbn9Ra3tACVviJjA87Beg7YCqtaPUBJFDHihtWMOfqIAuakyV52tBuhZbIcRrcDFM7N6Htb6WUr7GWCpNljV+GxV+cwG0dGBB3SSUmBCFJXViaqzVaL/VgA9YzXxOvFrr+sCStm+EUMVL3zbCxaEbvj3GcENfqnWbeSCUMOTsPJBSCQ6JIetKB2xbFU2C7rAzxIyez6AiBKUS/um6UXlNfWS7Glcq33jD7SDBxBjLeByLD6ruN9dvtXeOPP7ebJOhPU1qISTWNQtbiccT7RhX1YTMTMH4ylDqVqTezZ/VrEunczq0fw== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 7/2/26 07:13, Dev Jain wrote: > try_to_migrate_one() is used by folio migration to replace a present > mapping with a migration entry. For hugetlb folios, page_vma_mapped_walk() > returns the pte pointer to the hugetlb folio in pvmw.pte, but the code > reads the huge pte entry with ptep_get(). > > On arches which provide their own huge_ptep_get() to dereference a huge > pte pointer, accessing via ptep_get() would cause pte_pfn(), pte_present() > etc to misbehave. > > It is not clear whether this has a trivially visible effect to userspace. > > Use huge_ptep_get() to dereference a huge pte pointer. > > Commit a98a2f0c8ce1 copied the bug from try_to_unmap_one into > try_to_migrate_one. > > Fixes: a98a2f0c8ce1 ("mm/rmap: split migration into its own function") > Cc: stable@vger.kernel.org > Acked-by: Muchun Song > Signed-off-by: Dev Jain > --- > mm/rmap.c | 16 ++++++++++------ > 1 file changed, 10 insertions(+), 6 deletions(-) > > diff --git a/mm/rmap.c b/mm/rmap.c > index aa8a254efaecc..abc3a44baaa3d 100644 > --- a/mm/rmap.c > +++ b/mm/rmap.c > @@ -2505,11 +2505,16 @@ static bool try_to_migrate_one(struct folio *folio, struct vm_area_struct *vma, > /* Unexpected PMD-mapped THP? */ > VM_BUG_ON_FOLIO(!pvmw.pte, folio); > > - /* > - * Handle PFN swap PTEs, such as device-exclusive ones, that > - * actually map pages. > - */ > - pteval = ptep_get(pvmw.pte); > + address = pvmw.address; > + if (folio_test_hugetlb(folio)) { > + pteval = huge_ptep_get(mm, address, pvmw.pte); > + } else { > + /* > + * Handle PFN swap PTEs, such as device-exclusive ones, > + * that actually map pages. > + */ Again, the comment is related to the pte_present() handling, so best to move it down there. Apart from that LGTM. -- Cheers, David