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Wed, 25 Jun 2025 23:10:28 -0700 (PDT) Message-ID: <8bb4e188-eb3b-4ee3-88cc-93c826b04ef8@suse.com> Date: Thu, 26 Jun 2025 08:10:16 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC PATCH v4 5/8] xen/domctl: extend XEN_DOMCTL_assign_device to handle not only iommu To: Oleksii Moisieiev Cc: "xen-devel@lists.xenproject.org" , Andrew Cooper , Anthony PERARD , Bertrand Marquis , Juergen Gross , Julien Grall , Michal Orzel , =?UTF-8?Q?Roger_Pau_Monn=C3=A9?= , Volodymyr Babchuk , Grygorii Strashko , Stefano Stabellini References: <4f58bf9c47c40413ee9250c4cd21458382aac857.1747669845.git.oleksii_moisieiev@epam.com> <1780646c-cb6f-4508-86c8-a573fbc09f6a@epam.com> <1e116116-ddf7-4640-9809-2502203abe46@suse.com> <3e190e60-74a4-4565-acae-3b8602a4c46e@epam.com> Content-Language: en-US From: Jan Beulich Autocrypt: addr=jbeulich@suse.com; keydata= xsDiBFk3nEQRBADAEaSw6zC/EJkiwGPXbWtPxl2xCdSoeepS07jW8UgcHNurfHvUzogEq5xk hu507c3BarVjyWCJOylMNR98Yd8VqD9UfmX0Hb8/BrA+Hl6/DB/eqGptrf4BSRwcZQM32aZK 7Pj2XbGWIUrZrd70x1eAP9QE3P79Y2oLrsCgbZJfEwCgvz9JjGmQqQkRiTVzlZVCJYcyGGsD /0tbFCzD2h20ahe8rC1gbb3K3qk+LpBtvjBu1RY9drYk0NymiGbJWZgab6t1jM7sk2vuf0Py O9Hf9XBmK0uE9IgMaiCpc32XV9oASz6UJebwkX+zF2jG5I1BfnO9g7KlotcA/v5ClMjgo6Gl MDY4HxoSRu3i1cqqSDtVlt+AOVBJBACrZcnHAUSuCXBPy0jOlBhxPqRWv6ND4c9PH1xjQ3NP nxJuMBS8rnNg22uyfAgmBKNLpLgAGVRMZGaGoJObGf72s6TeIqKJo/LtggAS9qAUiuKVnygo 3wjfkS9A3DRO+SpU7JqWdsveeIQyeyEJ/8PTowmSQLakF+3fote9ybzd880fSmFuIEJldWxp Y2ggPGpiZXVsaWNoQHN1c2UuY29tPsJgBBMRAgAgBQJZN5xEAhsDBgsJCAcDAgQVAggDBBYC AwECHgECF4AACgkQoDSui/t3IH4J+wCfQ5jHdEjCRHj23O/5ttg9r9OIruwAn3103WUITZee e7Sbg12UgcQ5lv7SzsFNBFk3nEQQCACCuTjCjFOUdi5Nm244F+78kLghRcin/awv+IrTcIWF hUpSs1Y91iQQ7KItirz5uwCPlwejSJDQJLIS+QtJHaXDXeV6NI0Uef1hP20+y8qydDiVkv6l IreXjTb7DvksRgJNvCkWtYnlS3mYvQ9NzS9PhyALWbXnH6sIJd2O9lKS1Mrfq+y0IXCP10eS FFGg+Av3IQeFatkJAyju0PPthyTqxSI4lZYuJVPknzgaeuJv/2NccrPvmeDg6Coe7ZIeQ8Yj t0ARxu2xytAkkLCel1Lz1WLmwLstV30g80nkgZf/wr+/BXJW/oIvRlonUkxv+IbBM3dX2OV8 AmRv1ySWPTP7AAMFB/9PQK/VtlNUJvg8GXj9ootzrteGfVZVVT4XBJkfwBcpC/XcPzldjv+3 HYudvpdNK3lLujXeA5fLOH+Z/G9WBc5pFVSMocI71I8bT8lIAzreg0WvkWg5V2WZsUMlnDL9 mpwIGFhlbM3gfDMs7MPMu8YQRFVdUvtSpaAs8OFfGQ0ia3LGZcjA6Ik2+xcqscEJzNH+qh8V m5jjp28yZgaqTaRbg3M/+MTbMpicpZuqF4rnB0AQD12/3BNWDR6bmh+EkYSMcEIpQmBM51qM EKYTQGybRCjpnKHGOxG0rfFY1085mBDZCH5Kx0cl0HVJuQKC+dV2ZY5AqjcKwAxpE75MLFkr wkkEGBECAAkFAlk3nEQCGwwACgkQoDSui/t3IH7nnwCfcJWUDUFKdCsBH/E5d+0ZnMQi+G0A nAuWpQkjM1ASeQwSHEeAWPgskBQL In-Reply-To: <3e190e60-74a4-4565-acae-3b8602a4c46e@epam.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 25.06.2025 21:56, Oleksii Moisieiev wrote: > > On 23/06/2025 10:15, Jan Beulich wrote: >> On 19.06.2025 18:15, Oleksii Moisieiev wrote: >>> On 18/06/2025 03:04, Stefano Stabellini wrote: >>>> On Thu, 12 Jun 2025, Oleksii Moisieiev wrote: >>>>>>> diff --git a/xen/arch/arm/firmware/sci.c b/xen/arch/arm/firmware/sci.c >>>>>>> index e1522e10e2..8efd541c4f 100644 >>>>>>> --- a/xen/arch/arm/firmware/sci.c >>>>>>> +++ b/xen/arch/arm/firmware/sci.c >>>>>>> @@ -126,6 +126,43 @@ int sci_assign_dt_device(struct domain *d, struct dt_device_node *dev) >>>>>>> return 0; >>>>>>> } >>>>>>> >>>>>>> +int sci_do_domctl(struct xen_domctl *domctl, struct domain *d, >>>>>>> + XEN_GUEST_HANDLE_PARAM(xen_domctl_t) u_domctl) >>>>>>> +{ >>>>>>> + struct dt_device_node *dev; >>>>>>> + int ret = 0; >>>>>>> + >>>>>>> + switch ( domctl->cmd ) >>>>>>> + { >>>>>>> + case XEN_DOMCTL_assign_device: >>>>>>> + ret = -EOPNOTSUPP; >>>>>> Are you sure -EOPNOTSUPP is the right error code for the 3 checks below? >>>>> The -EOPNOTSUPP code is used because this is part of a chained call after >>>>> iommu_do_domctl, as stated in xen/common/domctl.c:859. The >>>>> XEN_DOMCTL_assign_device >>>>> call is expected to handle any DT device, regardless of whether the DT >>>>> device is >>>>> protected by an IOMMU or if the IOMMU is disabled. >>>>> The following cases are considered: >>>>> >>>>> 1. IOMMU Protected Device (Success) >>>>> >>>>> If the device is protected by the IOMMU and iommu_do_domctl returns 0, >>>>> we continue >>>>> processing the DT device by calling sci_do_domctl. >>>>> >>>>> 2. IOMMU Disabled (-EOPNOTSUPP from iommu_do_domctl) >>>>> >>>>> If iommu_do_domctl returns -EOPNOTSUPP, indicating that the IOMMU is >>>>> disabled, >>>>> we still proceed to call sci_do_domctl. >>>> OK this makes sense. I think it is OK to have a special error code to >>>> say "the IOMMU is disabled" but I don't know if it is a good idea to try >>>> to use -EOPNOTSUPP for that. -EOPNOTSUPP could mean a hypervisor >>>> configuration with domctl disabled, for instance. >>>> >>>> It might be wiser to use a different error code. Maybe ENOENT? >>>> >>> I see that in the following commit: >>> >>> 71e617a6b8 (use is_iommu_enabled() where appropriate..., 2019-09-17) >>> >>> -ENOSYS return code was changed to -EOPNOTSUPP in iommu_do_domctl. >>> >>> It's not clear to me why this was done from the commit description. >> This has been discussed many times elsewhere. Many of our ENOSYS uses are >> simply wrong. ENOSYS has very limited applicability: Unavailability of a >> top-level hypercall (originally: syscall). >> > What is your opinion about changing it to -ENOENT to say "the IOMMU is > disabled" as Stefano suggested in [0]? > > [0]: https://lists.xen.org/archives/html/xen-devel/2025-06/msg01233.html To me, ENOENT is closer to ENODEV, and hence not overly applicable here. If you want to avoid EOPNOTSUPP for whatever reason, how about ENXIO or EIO? (EPERM might also be an option, but we assign that a different meaning generally.) Jan