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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: dc8573a7-dfdf-4845-4d07-08db9250b831 X-MS-Exchange-CrossTenant-originalarrivaltime: 01 Aug 2023 05:32:38.8080 (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: wNolo2pck4r082cGsTYXvAgD8JjOSeLE7wyADw9Se6Q3aTFoUwt/hB60GMIEYvmNfX7sNuo1mrj2fQQ6AV+Wj8/vWDvaSeqVbXAcKjW6Zn8= X-MS-Exchange-Transport-CrossTenantHeadersStamped: CH0PR11MB5283 X-OriginatorOrg: intel.com X-Rspamd-Server: rspam08 X-Rspamd-Queue-Id: ED43F1C0014 X-Stat-Signature: a5iwk79r6rytaauxneo9fpzhen3nqkm4 X-Rspam-User: X-HE-Tag: 1690867963-28160 X-HE-Meta: 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 f+ZUG1jE iLIw4uZkU93EZ2FC6pCbFSJOni8J+LVDJAH461AnsusTY0hW/l6uYrQit88kLW/ogoz2daZ9UiwSRW8Jr0SKma5bVTllwuYa7oaWSw3qbzLBYMhRXyVJNChXdBQUx0jSB41TzEVsB17uZRYdfvO5oJAdS+Q9BSm/uAqPlCnPCqfhzqfrxljSoPgdHv+LJq3WkVT6Xt2tpRznwPKx77ZGfDS3bqulxoo3l6IhpVfUPSTYPhDiPLSCpWfnHPnFik2K0S8naHCxNrX5PMpR36bbscIyhQ6+Vm0fdAbBrWTmuNXfg63lGm0QpAZ0md2WisdXJVQw2ScLDNqLcmz9D/esZDaTuznzm+8fUcVMl8DGjLF9S6beeUZg0TQe9uBnodU2iBYNMhJbUVmygoMruDM/EGeCbB9ZYt8ZaABw8FS8xwr7Qwd2Kvlbj0iUJ7c/tBszwfSeDVXeswx4O2Jc= X-Bogosity: Ham, tests=bogofilter, spamicity=0.003680, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: Hi Jason, >=20 > > > Later the importer decides it needs the memory again so it again asks > > > for the dmabuf to be present, which does hmm_range_fault and gets > > > whatever is appropriate at the time. > > Unless I am missing something, I think just doing the above still won't= solve > > the problem. Consider this sequence: > > write_to_memfd(addr1, size, 'a'); > > buf =3D create_udmabuf_list(devfd, memfd, size); > > addr2 =3D mmap_fd(buf, NUM_PAGES * NUM_ENTRIES * getpagesize()); > > read(addr2); > > write_to_memfd(addr1, size, 'b'); > > punch_hole(memfd, MEMFD_SIZE / 2); > > -> Since we can process the invalidate at this point, as per your sugge= stion, > > we can trigger dmabuf move to let the importers know that the > dmabuf's > > backing memory has changed (or moved). > > > > read(addr2); > > -> Because there is a hole, we can handle the read by either providing = the > > old pages or zero pages (if using hmm_range_fault()) to the > > importers. >=20 > You never provide the old pages. After trunctate the only correct > value to read is zero. >=20 > > Maybe it is against convention, but I think it makes sense to prov= ide old > > pages (that were mapped before the hole punch) because the importe= rs > > have not read the data in these pages ('b' above) yet. >=20 > Nope. >=20 > > And, another reason to provide old pages is because the data in > > these pages is shown in a window on the Host's screen so it > > doesn't make sense to show zero page data. >=20 > So why did you trucate it if you want to keep the data? >=20 >=20 > > -> write_to_memfd(addr1, size, 'c'); > > As the hole gets refilled (with new pages) after the above write, = AFAIU, > we > > have to tell the importers again that since the backing memory has > changed, > > (new pages) they need to recreate their mappings. But herein lies = the > problem: > > from inside the udmabuf driver, we cannot know when this write occ= urs, > so we > > would not be able to notify the importers of the dmabuf move. >=20 > You get another invalidate because the memfd removes the zero pages > that hmm_range_fault installed in the PTEs before replacing them with > actual writable pages. Then you do the move, and another > hmm_range_fault, and basically the whole thing over again. Except this > time instead of returning zero pages it returns actual writable page. Ok, when I tested earlier (by registering an invalidate callback) but witho= ut hmm_range_fault(), I did not find this additional invalidate getting trigge= red. Let me try with hmm_range_fault() and see if everything works as expected. Thank you for your help. Thanks, Vivek >=20 > Jason