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AJvYcCW6FXkBKeJeqazQfJ2yGvvtHhAMe1gzDnfskMiG2bWY7yuY62O/VVnV6Gij1fa5gw2JyG4BYzDQeIoR3WU=@vger.kernel.org X-Gm-Message-State: AOJu0Yz5DJ6McOjVqP1ktCp5ciOC3M2J33e3FS0aJhyGUcawUcSIvXiQ BDGxznWvmnzSFu00/voFtTBpyha4ESyC+c/L+biAFC7PMiD6haGwTpFfmEk/h9l9Vw0Qs4IVBQb MTIWcVA== 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> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: 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" 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.