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charset="us-ascii" Content-Transfer-Encoding: quoted-printable Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-OriginatorOrg: microsoft.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-AuthSource: KUZP153MB1444.APCP153.PROD.OUTLOOK.COM X-MS-Exchange-CrossTenant-Network-Message-Id: 01ff478e-ff96-4489-91bb-08dd8f23baad X-MS-Exchange-CrossTenant-originalarrivaltime: 09 May 2025 18:02:57.4554 (UTC) X-MS-Exchange-CrossTenant-fromentityheader: Hosted X-MS-Exchange-CrossTenant-id: 72f988bf-86f1-41af-91ab-2d7cd011db47 X-MS-Exchange-CrossTenant-mailboxtype: HOSTED X-MS-Exchange-CrossTenant-userprincipalname: yHAIvM9nJFf6BA77C6Rqc1h9i0FuIOmShfxDmVSmNHROukv5xjxTKaYAaWusumjy/CYsBHvi/HRc4ERc3C4AGw== X-MS-Exchange-Transport-CrossTenantHeadersStamped: SIAP153MB1340 > -----Original Message----- > From: Wei Liu > Sent: 08 May 2025 23:33 > To: Roman Kisel > Cc: Saurabh Singh Sengar ; Naman Jain > ; KY Srinivasan ; > Haiyang Zhang ; Wei Liu ; > Dexuan Cui ; Anirudh Rayabharam > ; Saurabh Sengar > ; Stanislav Kinsburskii > ; Nuno Das Neves > ; linux-kernel@vger.kernel.org; linux- > hyperv@vger.kernel.org > Subject: [EXTERNAL] Re: [PATCH] Drivers: hv: Introduce mshv_vtl driver >=20 > On Wed, May 07, 2025 at 12:20:36PM -0700, Roman Kisel wrote: > > > > > > On 5/7/2025 6:02 AM, Saurabh Singh Sengar wrote: > > > > > [..] > > > > > > + } > > > > + > > > > + local_irq_save(flags); > > > > + in =3D *this_cpu_ptr(hyperv_pcpu_input_arg); > > > > + out =3D *this_cpu_ptr(hyperv_pcpu_output_arg); > > > > + > > > > + if (copy_from_user(in, (void __user *)hvcall.input_ptr, > > > > hvcall.input_size)) { > > > > > > Here is an issue related to usage of user copy functions when interru= pt are > disabled. > > > It was reported by Michael K here: > > > https://nam06.safelinks.protection.outlook.com/?url=3Dhttps%3A%2F%2Fg= i > > > thub.com%2Fmicrosoft%2FOHCL-Linux- > Kernel%2Fissues%2F33&data=3D05%7C02% > > > > 7Cssengar%40microsoft.com%7C3a21fc17545e4bafb86e08dd8e5aa427%7C72 > f98 > > > > 8bf86f141af91ab2d7cd011db47%7C1%7C0%7C638823242185564641%7CUnk > nown%7 > > > > CTWFpbGZsb3d8eyJFbXB0eU1hcGkiOnRydWUsIlYiOiIwLjAuMDAwMCIsIlAiOiJ > XaW4 > > > > zMiIsIkFOIjoiTWFpbCIsIldUIjoyfQ%3D%3D%7C0%7C%7C%7C&sdata=3DpdQ90a > aKZsy > > > 67qkPZkV4BfpwM6cM6scUbTeH9lT7s6s%3D&reserved=3D0 > > > > From the practical point of view, that memory will be touched by the > > user mode by virtue of Rust requiring initialization so the a possible > > page fault would be resolved before the IOCTL. OpenHCL runs without > > swap so the the memory will not be paged out to require page faults to > > be brought in back. > > > > I do agree that might be turned into a footgun by the user land if > > they malloc a page w/o prefaulting (so it's just a VA range, not > > backed with the physical page), and then send its address straight > > over here right after w/o writing any data to it. Perhaps likelier > > with the output data. Anyway, yes, relying on the user land doing sane > > things isn't the best approach to the kernel programming. >=20 > Yep. We don't rely on user land software doing sane things to maintain > correctness in kernel, so this needs to be fixed. >=20 > Thanks, > Wei. How about fixing this for normal x86 for now and put a TODO for CVM to be f= ixed later, when we bring in CVM support ? Regards, Saurabh