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Tue, 4 Nov 2025 14:50:43 +0000 Received: from MN2PR12MB3613.namprd12.prod.outlook.com ([fe80::1b3b:64f5:9211:608b]) by MN2PR12MB3613.namprd12.prod.outlook.com ([fe80::1b3b:64f5:9211:608b%4]) with mapi id 15.20.9298.006; Tue, 4 Nov 2025 14:50:43 +0000 Date: Tue, 4 Nov 2025 10:50:41 -0400 From: Jason Gunthorpe To: Eric Auger Cc: Shameer Kolothum , qemu-arm@nongnu.org, qemu-devel@nongnu.org, peter.maydell@linaro.org, nicolinc@nvidia.com, ddutile@redhat.com, berrange@redhat.com, nathanc@nvidia.com, mochs@nvidia.com, smostafa@google.com, wangzhou1@hisilicon.com, jiangkunkun@huawei.com, jonathan.cameron@huawei.com, zhangfei.gao@linaro.org, zhenzhong.duan@intel.com, yi.l.liu@intel.com, kjaju@nvidia.com Subject: Re: [PATCH v5 28/32] hw/arm/smmuv3-accel: Add property to specify OAS bits Message-ID: <20251104145041.GE1537560@nvidia.com> References: <20251031105005.24618-1-skolothumtho@nvidia.com> <20251031105005.24618-29-skolothumtho@nvidia.com> <49215c9d-feb1-4f72-bfe0-799572ecfac2@redhat.com> Content-Type: text/plain; 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envelope-from=jgg@nvidia.com; helo=CO1PR03CU002.outbound.protection.outlook.com X-Spam_score_int: -18 X-Spam_score: -1.9 X-Spam_bar: - X-Spam_report: (-1.9 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.788, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, FORGED_SPF_HELO=1, SPF_HELO_PASS=-0.001, SPF_NONE=0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-arm@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-arm-bounces+qemu-arm=archiver.kernel.org@nongnu.org Sender: qemu-arm-bounces+qemu-arm=archiver.kernel.org@nongnu.org On Tue, Nov 04, 2025 at 03:35:42PM +0100, Eric Auger wrote: > > + /* > > + * TODO: OAS is not something Linux kernel doc says meaningful for user. > > + * But looks like OAS needs to be compatible for accelerator support. Please > > + * check. > would remove that comment. Either it is requested or not. > > + */ > > + if (FIELD_EX32(info->idr[5], IDR5, OAS) < > > + FIELD_EX32(s->idr[5], IDR5, OAS)) { > > + error_setg(errp, "Host SMMUv3 OAS(%d) bits not compatible", > > + smmuv3_oas_bits(FIELD_EX32(info->idr[5], IDR5, OAS))); > let's be more explicit then and say > > Host SMMUv3 OAS (%d bits) is less that OAS bits advertised by SMMU (%d) It isn't OAS that is being checked here, this is now IPA. OAS is for use by the hypervisor. When the guest looks at the vSMMU the "OAS" it sees is the IPS supported by the HW. Aside from the raw HW limit, it also shouldn't exceed the configured size of the S2 HWPT. So the above should refer to this detail because it is a bit subtle that OAS and IPS are often the same. See "3.4 Address sizes" * IAS reflects the maximum usable IPA of an implementation that is generated by stage 1 and input to stage 2: - This term is defined to illustrate the handling of intermediate addresses in this section and is not a configurable parameter. - The maximum usable IPA size of an SMMU is defined in terms of other SMMU implementation choices, as: IAS = MAX(SMMU_IDR0.TTF[0]==1 ? 40 : 0), SMMU_IDR0.TTF[1]==1 ? OAS : 0)); - An IPA of 40 bits is required to support of AArch32 LPAE translations, and AArch64 limits the maximum IPA size to the maximum PA size. Otherwise, when AArch32 LPAE is not implemented, the IPA size equals OAS, the PA size, and might be smaller than 40 bits. - The purpose of definition of the IAS term is to abstract away from these implementation variables. Jason