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charset="us-ascii" Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-AuthSource: IA0PR11MB7185.namprd11.prod.outlook.com X-MS-Exchange-CrossTenant-Network-Message-Id: f9d5b7a0-6b03-4a02-6003-08db88200aff X-MS-Exchange-CrossTenant-originalarrivaltime: 19 Jul 2023 06:19:00.7436 (UTC) X-MS-Exchange-CrossTenant-fromentityheader: Hosted X-MS-Exchange-CrossTenant-id: 46c98d88-e344-4ed4-8496-4ed7712e255d X-MS-Exchange-CrossTenant-mailboxtype: HOSTED X-MS-Exchange-CrossTenant-userprincipalname: Jv7As6FpnA+GVCKW4GM1wCVAmD//aAHF51eG/fw22Faya7QlSXe225jMq0N07hK7U2Gt5co9gJDSCr7uhCXd0Gj5/VZAipvRQZ90HahY8n0= X-MS-Exchange-Transport-CrossTenantHeadersStamped: PH8PR11MB8014 X-OriginatorOrg: intel.com X-Rspamd-Queue-Id: 9794D10001B X-Rspam-User: X-Stat-Signature: zx633xmma6qoash7srojhydzxy4iokie X-Rspamd-Server: rspam01 X-HE-Tag: 1689747545-536062 X-HE-Meta: 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 +kCZqY24 0s/9pEp1jJkm9lv8yvlhJynCYL2knge8It+tnMlEAQWUwbDb6w0fSlqBm5SWPnVulU7pQpg9geaYOD0SFR/JfdWsPTY/KEKtSXOsLpG+4wjZs5t7H12tOz2YErAuKPvb0y39Ogeh0IBDglaXNTtNNXk/8fk7GylW2wzEZKFiFafQ8w2gHfslX3ABeMSrPHL5sBdDvzi2eE6CCtPTVepZTJ9Ob8VHyyrMglcMvs77iTaOjPx6ZU+0oymJqeA8PxUH/wGe799G3eiotf/WKQ9i0KK7Yjl4SlaEJAB/Pl3i98qforPae5+2UNwhw14On+e7AGAmb0NBFp07NXvYfhi+6fK3vxFUYcQ65on+t47HiTk56Po1fYQDK/m7xrWxxYZWFlYyX 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: Hi Jason, >=20 > On Wed, Jul 19, 2023 at 12:05:29AM +0000, Kasireddy, Vivek wrote: >=20 > > > If there is no change to the PTEs then it is hard to see why this > > > would be part of a mmu_notifier. > > IIUC, the PTEs do get changed but only when a new page is faulted in. > > For shmem, it looks like the PTEs are updated in handle_pte_fault() > > after shmem_fault() gets called and for hugetlbfs, this seems to > > happen in hugetlb_fault(). >=20 > That sounds about right >=20 > > Instead of introducing a new notifier, I did think about reusing > > (or overloading) .change_pte() but I did not fully understand the impac= t > > it would have on KVM, the only user of .change_pte(). >=20 > Yes, change_pte will be called, I think, but under various locks.=20 AFAICT, change_pte does not seem to get called in my use-case either during invalidate or when a new page is faulted in. >Why would you need to change it? What I meant to say is instead of adding a new notifier for mapping updates= , I initially considered just calling change_pte() when a new page is faulted= in but I was concerned that doing so might adversely impact existing users (of change_pte) such as KVM. >=20 > What you are doing here doesn't make any sense within the design of > mmu_notifiers, eg: >=20 > > @ -2164,8 +2165,12 @@ static vm_fault_t shmem_fault(struct vm_fault > *vmf) > > gfp, vma, vmf, &ret); > > if (err) > > return vmf_error(err); > > - if (folio) > > + if (folio) { > > vmf->page =3D folio_file_page(folio, vmf->pgoff); > > + if (ret =3D=3D VM_FAULT_LOCKED) > > + mmu_notifier_update_mapping(vma->vm_mm, vmf- > >address, > > + page_to_pfn(vmf->page)); > > + } > > return ret; >=20 > Hasn't even updated the PTEs yet, but it is invoking a callback?? I was counting on the fragile assumption that once we have a valid page, the PTE would be eventually updated after shmem_fault(), which doesn't make sense in retrospect. Instead, would something like below be OK? @@ -5234,6 +5237,14 @@ vm_fault_t handle_mm_fault(struct vm_area_struct *vm= a, unsigned long address, lru_gen_exit_fault(); + if (vma_is_shmem(vma) || is_vm_hugetlb_page(vma)) { + if (!follow_pte(vma->vm_mm, address, &ptep, &ptl)) { + pfn =3D pte_pfn(ptep_get(ptep)); + pte_unmap_unlock(ptep, ptl); + mmu_notifier_update_mapping(vma->vm_mm, address, pf= n); + } + } Thanks, Vivek >=20 > Jason