[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] [PATCH v3 3/3] xen/arm: introduce XENFEAT_grant_map_identity
On 07/24/2014 04:02 PM, Stefano Stabellini wrote: > On Thu, 24 Jul 2014, Julien Grall wrote: >> On 07/24/2014 03:43 PM, Jan Beulich wrote: >>>>>> On 24.07.14 at 16:10, <stefano.stabellini@xxxxxxxxxxxxx> wrote: >>>> On Thu, 24 Jul 2014, Jan Beulich wrote: >>>>>>>> On 24.07.14 at 15:31, <stefano.stabellini@xxxxxxxxxxxxx> wrote: >>>>>> --- a/xen/common/grant_table.c >>>>>> +++ b/xen/common/grant_table.c >>>>>> @@ -727,7 +727,7 @@ __gnttab_map_grant_ref( >>>>>> >>>>>> double_gt_lock(lgt, rgt); >>>>>> >>>>>> - if ( gnttab_need_iommu_mapping(ld) ) >>>>>> + if ( gnttab_need_iommu_mapping(ld) || >>>>>> gnttab_need_identity_mapping(ld) >>>> ) >>>>> >>>>> As before I think this change is pointless. >>>> >>>> I don't understand how you propose to solve the problem. >>> >>> I think ARM's gnttab_need_iommu_mapping() needs to just be >>> is_domain_direct_mapped() then. > > That's not correct either. It would work, but it is conceptually wrong. > From the ARM perspective we have 2 distinct cases to cover: > - we have an smmu and we need to create a mapping for it > - we don't have an smmu and we need an identity mapping > > >> So ARM people will think we need an iommu to add the identity mapping. >> Why don't we rename gnttab_need_iommu_mapping into >> gnttab_need_identity_mapping? >> >> It would less confusing for both x86 and ARM. > > I don't think that would be any better. > We have 2 distinct cases to cover, we need to treat them as such. The cases are not so distinct. We need the 1:1 grant mapping for the IOMMU because of the swiotlb and the 1:1 memory mapping. Without it we can easily bypass this code. -- Julien Grall _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxx http://lists.xen.org/xen-devel
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