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X-OriginatorOrg: amd.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 15 Jan 2026 20:43:03.8316 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: 447c09c7-1556-4b3a-919f-08de5476ae38 X-MS-Exchange-CrossTenant-Id: 3dd8961f-e488-4e60-8e11-a82d994e183d X-MS-Exchange-CrossTenant-OriginalAttributedTenantConnectingIp: TenantId=3dd8961f-e488-4e60-8e11-a82d994e183d;Ip=[165.204.84.17];Helo=[satlexmb07.amd.com] X-MS-Exchange-CrossTenant-AuthSource: DS3PEPF000099DA.namprd04.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: BL3PR12MB6620 On Thu, Jan 15, 2026 at 11:17:18AM -0800, Sean Christopherson wrote: > 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. Thanks for the catch. FWIW I double-checked that kvm_gmem_get_folio() always returns an ERR_PTR() instead of NULL directly, so the suggested change looks good to me. -Mike