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AJvYcCXFIsqvUxss16kTCDnH720zJKd2KKKYO1p2UGuR/5BLVHcid0hjBj22HZ6l5SHcj/3h9McxZdGSUA==@kvack.org X-Gm-Message-State: AOJu0YyKRTiz4y6J6q/2maeppuEhI33UIUr5vl9X++N6CyMUBgR/EObE 4HtkMKfX15pZ2MgkP1bb8vBodaIY1E7QiLXMh9Z8PUH2bQWI8C4rKRbPEIRWPVXqYsNqBkTtUNQ mDad3FQ== X-Received: from pfbbj16.prod.google.com ([2002:a05:6a00:3190:b0:7b8:922c:725d]) (user=seanjc job=prod-delivery.src-stubby-dispatcher) by 2002:a05:6a00:2ea0:b0:81f:3d13:e070 with SMTP id d2e1a72fcca58-81fa17729e5mr189167b3a.12.1768504640018; Thu, 15 Jan 2026 11:17:20 -0800 (PST) Date: Thu, 15 Jan 2026 11:17:18 -0800 In-Reply-To: <20260108214622.1084057-3-michael.roth@amd.com> Mime-Version: 1.0 References: <20260108214622.1084057-1-michael.roth@amd.com> <20260108214622.1084057-3-michael.roth@amd.com> Message-ID: Subject: Re: [PATCH v3 2/6] KVM: guest_memfd: Remove partial hugepage handling from kvm_gmem_populate() From: Sean Christopherson To: Michael Roth Cc: kvm@vger.kernel.org, linux-coco@lists.linux.dev, linux-mm@kvack.org, linux-kernel@vger.kernel.org, thomas.lendacky@amd.com, pbonzini@redhat.com, vbabka@suse.cz, ashish.kalra@amd.com, liam.merwick@oracle.com, david@redhat.com, vannapurve@google.com, ackerleytng@google.com, aik@amd.com, ira.weiny@intel.com, yan.y.zhao@intel.com, pankaj.gupta@amd.com, Kai Huang Content-Type: text/plain; charset="us-ascii" X-Rspamd-Server: rspam03 X-Rspamd-Queue-Id: 6C7F6100003 X-Stat-Signature: sn9hsf7nicffrq7m97uyxxgu9jminrrc X-Rspam-User: X-HE-Tag: 1768504641-827995 X-HE-Meta: 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 3UjgyBLT fy9mKbZx/3aHAOoQdD/qY1CxZ6PKI2J7kclVdWb61jzck2pPYHkFFJNxYKn7s/0TZBpHUiWguwlbmtH1+79fRWVlW7+Osej+UvqYxHP1psr7WUpX9ToBI59Uy3FwzhNkIyjSqfmPYOdxeVk8NL8HoGesR63jAKWVnojoEwkrIrbGs8l1DnWEKZDRUtoVA24GuEHDM3ZilTIEKCuoEYY2AhtFimWe8nPqMOFE6Kyp0N985op8RUTAJR5p6NsPMJixhAbTFGoRg9aoIZTmV3i7U+vB0IemSi6Yuz+V/VwdohHhRYg5yFZyIqG6te2IsSrzbkGlUKTuF79lGrolY21b9Uerl6w== 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: List-Subscribe: List-Unsubscribe: On Thu, Jan 08, 2026, Michael Roth wrote: > diff --git a/virt/kvm/guest_memfd.c b/virt/kvm/guest_memfd.c > index fdaea3422c30..9dafa44838fe 100644 > --- a/virt/kvm/guest_memfd.c > +++ b/virt/kvm/guest_memfd.c > @@ -151,6 +151,15 @@ static struct folio *kvm_gmem_get_folio(struct inode *inode, pgoff_t index) > mapping_gfp_mask(inode->i_mapping), policy); > mpol_cond_put(policy); > > + /* > + * External interfaces like kvm_gmem_get_pfn() support dealing > + * with hugepages to a degree, but internally, guest_memfd currently > + * assumes that all folios are order-0 and handling would need > + * to be updated for anything otherwise (e.g. page-clearing > + * operations). > + */ > + WARN_ON_ONCE(folio_order(folio)); Gah, this is buggy. __filemap_get_folio_mpol() can return an ERR_PTR(). If that happens, this WARN will dereference garbage and explode. And of course I find it _just_ after sending thank yous, *sigh*. I'll squash to this (after testing): WARN_ON_ONCE(!IS_ERR(folio) && folio_order(folio)); avoiding a few emails isn't worth having a lurking bug.