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Wed, 29 Apr 2026 13:47:16 +0000 (GMT) Received: from li-008a6a4c-3549-11b2-a85c-c5cc2836eea2.ibm.com (unknown [9.52.215.75]) by smtpav02.fra02v.mail.ibm.com (Postfix) with ESMTPS; Wed, 29 Apr 2026 13:47:16 +0000 (GMT) Date: Wed, 29 Apr 2026 15:47:15 +0200 From: Alexander Gordeev To: "David Hildenbrand (Arm)" Cc: Andrew Morton , Lorenzo Stoakes , Gerald Schaefer , Heiko Carstens , Vasily Gorbik , linux-s390@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] mm/page_vma_mapped_walk: add missing pgtable entry accessors Message-ID: References: <20260427052000.196402-1-agordeev@linux.ibm.com> <69c4c12c-7cdc-4a17-9eb7-6fb1a61f9834@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <69c4c12c-7cdc-4a17-9eb7-6fb1a61f9834@kernel.org> X-TM-AS-GCONF: 00 X-Authority-Analysis: v=2.4 cv=AqDeGu9P c=1 sm=1 tr=0 ts=69f20be9 cx=c_pps a=bLidbwmWQ0KltjZqbj+ezA==:117 a=bLidbwmWQ0KltjZqbj+ezA==:17 a=kj9zAlcOel0A:10 a=A5OVakUREuEA:10 a=VkNPw1HP01LnGYTKEx00:22 a=RnoormkPH1_aCDwRdu11:22 a=U7nrCbtTmkRpXpFmAIza:22 a=VnNF1IyMAAAA:8 a=j5aMtUXh0naQkGdsk6gA:9 a=CjuIK1q_8ugA:10 X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwNDI5MDE0MCBTYWx0ZWRfXxTSLyxKf6Pf8 KNJ4rpP3Syi3oag+YKwk2Awq0cKPIrlvQRSHdzQTbeh8Q7+KoS2b+6HBEHa5H7lnQvExaY0Nrx0 uevRDFwpfxCIba8sG0GOWAgPBMRx6xMSD0lNsaf6BIrg9H/45oNt82xpQrzFf8KFTPtEP1AnK/V sCRL092IemCs/GOOUIP0XsCiubusBVz5L6NAK1+dAgkWAC7uPB/O8tsPT4IBhF+ugi63H97hCf1 IirZAWGGdvH7RW0veIlzaEdq0gN8CrRCNSu/FWoKPkXkfcatIQ3jif0uY4pixVvyZcB+5eha7e/ TVh3KwJiQ4mccDPASbBftAkKi44/MGwjNOrxJpITyVqjz/SJ4QTejhmU0RbU/cZ3YeKRNd7GW3I kRdRVtuMV+4zq5820dckDRlgBJf7IGzgLmgeewbRj4rGfSNNKZXmtPJuXC45/1uPEkQqR/3m2dw 23HZBNYyFad76jUnRAA== X-Proofpoint-GUID: yrv26ZzoKgHOt5QRWgP9HHSlaVzGQMv6 X-Proofpoint-ORIG-GUID: yrv26ZzoKgHOt5QRWgP9HHSlaVzGQMv6 X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1143,Hydra:6.1.51,FMLib:17.12.100.49 definitions=2026-04-28_05,2026-04-28_01,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 adultscore=0 priorityscore=1501 phishscore=0 suspectscore=0 clxscore=1015 lowpriorityscore=0 spamscore=0 bulkscore=0 impostorscore=0 malwarescore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2604200000 definitions=main-2604290140 X-Rspamd-Server: rspam03 X-Rspamd-Queue-Id: 5FEAC180013 X-Stat-Signature: eqzicugwschh5rpyd1nhor9gycoknrca X-Rspam-User: X-HE-Tag: 1777470444-301607 X-HE-Meta: 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 EdYOPKIB 6beeIRSbPPuPtVXfkN8eUY/fklP6KAvwCbSbOzSb6stw5VYNcgOqQNLdmVPCXgPpSZ2t6vFnYX2JbMc6bNDnRlkSBIvv/Ebp8yO9jQKYx2Sv5yoEmoR03kGea9rYL4Gu+92pICgxxdhKRU6TWmw3v84lyudC9sM7ehaxb1wX11zBEyk2nrzXGceDfBoDl/JD+JP6AkuyB8e29T5TzyeG9YFx9OrWM8cQiuuuLljTE22500Tb04nPoix0J/8RDoSBmxFka3umquV09nbyS0LQDPQ6GqFVoO3ZsiGNjySmFkfFSqqG7Hng5h9lp4G1AqYnmwtkvwuXA/Ekl35/QVR7SvPj1UeIqCaQg7DrZ2FtjPjfGFQRqAzxJJYpwzleAklhtdIm2 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Mon, Apr 27, 2026 at 11:02:50AM +0200, David Hildenbrand (Arm) wrote: > On 4/27/26 07:20, Alexander Gordeev wrote: > > Convert pgtable direct entry dereferences to the corresponding > > pXdp_get() accessors. Use ptep_get_lockless() variant for PTE > > reads when no lock is taken. > > > > Signed-off-by: Alexander Gordeev > > --- > > mm/page_vma_mapped.c | 12 ++++++------ > > 1 file changed, 6 insertions(+), 6 deletions(-) > > > > diff --git a/mm/page_vma_mapped.c b/mm/page_vma_mapped.c > > index b38a1d00c971..a4520bb10d2a 100644 > > --- a/mm/page_vma_mapped.c > > +++ b/mm/page_vma_mapped.c > > @@ -41,7 +41,7 @@ static bool map_pte(struct page_vma_mapped_walk *pvmw, pmd_t *pmdvalp, > > if (!pvmw->pte) > > return false; > > > > - ptent = ptep_get(pvmw->pte); > > + ptent = ptep_get_lockless(pvmw->pte); (*) > > if (pte_none(ptent)) { > > return false; > > @@ -219,17 +219,17 @@ bool page_vma_mapped_walk(struct page_vma_mapped_walk *pvmw) > > restart: > > do { > > pgd = pgd_offset(mm, pvmw->address); > > - if (!pgd_present(*pgd)) { > > + if (!pgd_present(pgdp_get(pgd))) { > > step_forward(pvmw, PGDIR_SIZE); > > continue; > > } > > p4d = p4d_offset(pgd, pvmw->address); > > - if (!p4d_present(*p4d)) { > > + if (!p4d_present(p4dp_get(p4d))) { > > step_forward(pvmw, P4D_SIZE); > > continue; > > } > > pud = pud_offset(p4d, pvmw->address); > > - if (!pud_present(*pud)) { > > + if (!pud_present(pudp_get(pud))) { > > step_forward(pvmw, PUD_SIZE); > > continue; > > Wasn't there a problem with folded page tables, where we would no longer be able > to optimize out the folded page table accesses? Ok, that is a different topic. I actually tried to resolve the lockless issue(s) in (*) while the direct dereferences just seemed to be relevant to go along (similarly to the GUP patch). But I would rather resend ptep_get() => ptep_get_lockless() fixes for this patch. Would it work? > I thought we discussed ways to resolve that. Let me dig ... > > > -- > Cheers, > > David Thanks!