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charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 X-OriginatorOrg: Nvidia.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-AuthSource: SA1PR12MB7199.namprd12.prod.outlook.com X-MS-Exchange-CrossTenant-Network-Message-Id: 29d2fab7-aefd-403c-8066-08dd60954694 X-MS-Exchange-CrossTenant-originalarrivaltime: 11 Mar 2025 12:07:20.6890 (UTC) X-MS-Exchange-CrossTenant-fromentityheader: Hosted X-MS-Exchange-CrossTenant-id: 43083d15-7273-40c1-b7db-39efd9ccc17a X-MS-Exchange-CrossTenant-mailboxtype: HOSTED X-MS-Exchange-CrossTenant-userprincipalname: kZvqco0S7Xi5Scq29lSIQdJVTX1ORgMMZnSjqx3AUZUCkCXAgIuN35ioZl42dfi30Z1sbm2KJMXoz6BWbpG66A== X-MS-Exchange-Transport-CrossTenantHeadersStamped: MN2PR12MB4223 X-Rspam-User: X-Rspamd-Queue-Id: 8B41A80021 X-Rspamd-Server: rspam03 X-Stat-Signature: gg9wrksq4yynjbrbdmk77kiz7ycaa1s6 X-HE-Tag: 1741694843-417778 X-HE-Meta: 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 5fIhyxty 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000215, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: Thanks Marc for the feedback.=0A= =0A= > No, I'm concerned that a well established API (populating a memslot)=0A= > works in some case and doesn't work in another without a clear=0A= > indication of *why* we have this behaviour.=0A= >=0A= > To me, this indicates that userspace needs to buy in this new=0A= > behaviour, and that behaviour needs to be advertised by a capability,=0A= > which is in turn conditional on FWB.=0A= =0A= Yes, that makes sense.=0A= =0A= >>> Perhaps we can gracefully fall back to the default device mapping=0A= >>> in such case? But that would cause VM to crash as soon as it makes some= =0A= >>> access violating DEVICE_nGnRE.=0A= >=0A= > Which would now be a regression...=0A= > =0A= > My take is that this cacheable PNFMAP contraption must only be exposed=0A= > to a guest if FWB is available. We can't prevent someone to do an=0A= > mmap() behind our back, but we can at least:=0A= >=0A= > - tell userspace whether this is supported=0A= =0A= For my education, what is an accepted way to communicate this? Please let= =0A= me know if there are any relevant examples that you may be aware of.=0A= =0A= I suppose just checking for FWB (for PFNMAP) and returning some sort of=0A= an error on userspace mmap will not be enough of a hint here?=0A= =0A= > - only handle the fault if userspace has bought in this mode=0A= > - report the fault to userspace for it to fix things otherwise=0A= >=0A= >=A0=A0=A0=A0=A0=A0=A0 M.=0A= >=0A= > --=0A= > Without deviation from the norm, progress is not possible.=