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b=N834jSyCk3yngtaInhSTG+aG4iD4w6O0KHMtgVlTqOx+RT2zRJM8Ge0bNuC95lKES F35F562EXYbYpH7wQgxqU3jb74BiX+6r51/mViDYvvuUoSD4ctLMG3fr4chrVBCwdU Ul+Albq0niCn0RkrWoHKs1b3kmnKJCe0kN4hDSWOc2tgwYINsivugwy0TCHQHzUdhz 0KvHhE5HNtPLKdnFhvJpx+UUWBhVdVU89CdxSctY/Q6M4ZdMnoPtJ4JXznUxBuZB8w iweT4tqzXWVWbQupowJAW9xgej6aBWiVbQwhPcxY3zZTXEXQZtBNac+fVEQkxwjTKw td0sCqy7VTvqA== Message-ID: From: sashiko-bot@kernel.org Subject: Re: [PATCH RFC v3 06/88] KVM: selftests: Add helper to create guest_memfd with a resource file Reply-To: sashiko-reviews@lists.linux.dev To: "Ackerley Tng" , "Alexey Kardashevskiy" , "Aneesh Kumar K.V" , "Christian Brauner" , "David Hildenbrand" , "David Woodhouse" , "Fred Griffoul" , "Jacob Pan" , "Jianxiong Gao" , "John Starks" , "Michael Roth" , "Paolo Bonzini" , "Samiullah Khawaja" , "Sean Christopherson" , "Suzuki K Poulose" , "Tarun Sahu" , "Vishal Annapurve" , "Xu Yilun" , "Fuad Tabba" Cc: kvm@vger.kernel.org, linux-mm@kvack.org In-Reply-To: <20261106-gmem-alternative-providers-v3-6-8484dde66a7e@google.com> References: <20261106-gmem-alternative-providers-v3-0-8484dde66a7e@google.com> <20261106-gmem-alternative-providers-v3-6-8484dde66a7e@google.com> Content-Type: text/plain; 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Sashiko AI review found 2 potential issues to consider: - [High] KVM: guest_memfd: missing release_folio() with mapping_set_release_always() - [Medium] mm: shmem: unmovable guest_memfd folios allocated with GFP_HIGHUSER_MOVABLE -- commit a3e5841f5c68c0e42d4540b30c82c6fced7d8d4f Author: Ackerley Tng KVM: selftests: Add helper to create guest_memfd with a resource file This commit syncs the KVM UAPI header for GUEST_MEMFD_FLAG_USE_RESOURCE and adds selftest helpers to create a guest_memfd instance backed by a resource file descriptor. > diff --git a/tools/testing/selftests/kvm/include/kvm_util.h b/tools/testi= ng/selftests/kvm/include/kvm_util.h > index e2618877619e1..eca296539db79 100644 > --- a/tools/testing/selftests/kvm/include/kvm_util.h > +++ b/tools/testing/selftests/kvm/include/kvm_util.h > @@ -809,26 +809,39 @@ static inline bool is_smt_on(void) > =20 > void vm_create_irqchip(struct kvm_vm *vm); > =20 > -static inline int __vm_create_guest_memfd(struct kvm_vm *vm, u64 size, > - u64 flags) > +static inline int __vm_create_guest_memfd_resource(struct kvm_vm *vm, u6= 4 size, > + u64 flags, int resource_fd) > { > struct kvm_create_guest_memfd guest_memfd =3D { > .size =3D size, > .flags =3D flags, > + .resource_fd =3D resource_fd, > }; > =20 > return __vm_ioctl(vm, KVM_CREATE_GUEST_MEMFD, &guest_memfd); > } [Severity: High] In the underlying kernel support for provider folio invalidation added earlier in this series in commit "KVM: guest_memfd: Support provider folio invalidation", kvm_gmem_init_inode() calls mapping_set_release_always(inode->i_mapping), but kvm_gmem_aops does not implement .release_folio. Can this cause mapping_evict_folio() to warn and evict guest_memfd folios without invalidating KVM MMU mappings or provider accounting? Because AS_RELEASE_ALWAYS is set, folio_needs_release() is true in filemap_release_folio(), which falls back to try_to_free_buffers() when a_ops->release_folio is NULL: fs/buffer.c:try_to_free_buffers() { /* Misconfigured folio check */ if (WARN_ON_ONCE(!folio_buffers(folio))) return true; When soft_offline_in_use_page() calls mapping_evict_folio() on a clean, unmapped guest_memfd folio, filemap_release_folio() triggers that warning and returns true. mapping_evict_folio() then removes the folio from the page cache without calling kvm_gmem_invalidate_folio() or notifying the KVM MMU, leaving stage-2 page tables pointing to the freed page and leaking tmpfs provider block accounting. > -static inline int vm_create_guest_memfd(struct kvm_vm *vm, u64 size, > - u64 flags) > +static inline int __vm_create_guest_memfd(struct kvm_vm *vm, u64 size, > + u64 flags) > +{ > + return __vm_create_guest_memfd_resource(vm, size, flags, 0); > +} > + > +static inline int vm_create_guest_memfd_resource(struct kvm_vm *vm, u64 = size, > + u64 flags, int resource_fd) > { > - int fd =3D __vm_create_guest_memfd(vm, size, flags); > + int fd =3D __vm_create_guest_memfd_resource(vm, size, flags, resource_f= d); > =20 > TEST_ASSERT(fd >=3D 0, KVM_IOCTL_ERROR(KVM_CREATE_GUEST_MEMFD, fd)); > return fd; > } [Severity: Medium] When a guest_memfd is created with a tmpfs resource_fd (via commit "mm: shmem: Implement guest_memfd provider operations for tmpfs" earlier in this series), does shmem_gmem_alloc_folio() place unmovable folios into ZONE_MOVABLE or MIGRATE_CMA? kvm_gmem_init_inode() sets GFP_HIGHUSER (without __GFP_MOVABLE) and marks the mapping AS_INACCESSIBLE because guest_memfd folios cannot be migrated. However, shmem_gmem_alloc_folio() allocates with GFP_HIGHUSER_MOVABLE: mm/shmem.c:shmem_gmem_alloc_folio() { ... if (mpol) folio =3D folio_alloc_mpol(GFP_HIGHUSER_MOVABLE, 0, mpol, index, numa_node_id()); else folio =3D folio_alloc(GFP_HIGHUSER_MOVABLE, 0); Once kvm_gmem_get_folio() inserts the folio into the AS_INACCESSIBLE guest_memfd mapping, migration is rejected, pinning the page in ZONE_MOVABLE or CMA and breaking CMA allocations or memory hot-unplug. --=20 Sashiko AI review =C2=B7 https://sashiko.dev/#/patchset/20261106-gmem-alter= native-providers-v3-0-8484dde66a7e@google.com?part=3D6