Hello Julien, > On 8 Feb 2021, at 6:11 pm, Julien Grall <jul...@xen.org> wrote: > > > > On 08/02/2021 18:06, Rahul Singh wrote: >>> On 6 Feb 2021, at 12:38 am, Stefano Stabellini <sstabell...@kernel.org> >>> wrote: >>> >>> Commit 91d4eca7add broke gnttab_need_iommu_mapping on ARM. >>> The offending chunk is: >>> >>> #define gnttab_need_iommu_mapping(d) \ >>> - (is_domain_direct_mapped(d) && need_iommu(d)) >>> + (is_domain_direct_mapped(d) && need_iommu_pt_sync(d)) >>> >>> On ARM we need gnttab_need_iommu_mapping to be true for dom0 when it is >>> directly mapped, like the old check did, but the new check is always >>> false. >>> >>> In fact, need_iommu_pt_sync is defined as dom_iommu(d)->need_sync and >>> need_sync is set as: >>> >>> if ( !is_hardware_domain(d) || iommu_hwdom_strict ) >>> hd->need_sync = !iommu_use_hap_pt(d); >>> >>> iommu_hwdom_strict is actually supposed to be ignored on ARM, see the >>> definition in docs/misc/xen-command-line.pandoc: >>> >>> This option is hardwired to true for x86 PVH dom0's (as RAM belonging to >>> other domains in the system don't live in a compatible address space), >>> and >>> is ignored for ARM. >>> >>> But aside from that, the issue is that iommu_use_hap_pt(d) is true, >>> hence, hd->need_sync is false, and gnttab_need_iommu_mapping(d) is false >>> too. >>> >>> As a consequence, when using PV network from a domU on a system where >>> IOMMU is on from Dom0, I get: >>> >>> (XEN) smmu: /smmu@fd800000: Unhandled context fault: fsr=0x402, >>> iova=0x8424cb148, fsynr=0xb0001, cb=0 >>> [ 68.290307] macb ff0e0000.ethernet eth0: DMA bus error: HRESP not OK >> I also observed the IOMMU fault when DOMU guest is created and great table >> is used when IOMMU is enabled. I fixed the error in different way but I am >> not sure if you also observing the same error. I submitted the patch to >> pci-passthrough integration branch. Please have a look once if that make >> sense. > > I belive this is the same error as Stefano has observed. However, your patch > will unfortunately not work if you have a system with a mix of protected and > non-protected DMA-capable devices.
Yes you are right thats what I though when I fixed the error but then I thought in different direction if IOMMU is enabled system wise every device should be protected by IOMMU. My understanding might be wrong. Regards, Rahul > Cheers, > > -- > Julien Grall
