[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] [PATCH v2 1/2] introduce GFN notification for translated domains
On 20.11.2019 21:22, Julien Grall wrote: > On 14/11/2019 16:43, Jan Beulich wrote: >> In order for individual IOMMU drivers (and from an abstract pov also >> architectures) to be able to adjust, ahead of actual mapping requests, >> their data structures when they might cover only a sub-range of all >> possible GFNs, introduce a notification call used by various code paths >> potentially installing a fresh mapping of a never used GFN (for a >> particular domain). > > If I understand this correctly, this is mostly targeting IOMMNU driver > where page-table are not shared with the processor. Right? Yes - with shared page tables there's no separate handling of IOMMU (un)mappings in the first place. >> TBD: Does Arm actually have anything to check against in its >> arch_notify_gfn()? > > I understand that we want to keep the code mostly generic, but I am a > bit concerned of the extra cost to use notify_gfn() (and indirectly > iommu_notify_gfn()) for doing nothing. > > I can't see any direct use of this for the foreseable future on Arm. So > could we gate this under a config option? This is an option, sure. Alternatively I could see about making this an inline function, but iirc there were header dependency issues. Then again - is a call to a function doing almost nothing really so much extra overhead on Arm? >> --- a/xen/common/grant_table.c >> +++ b/xen/common/grant_table.c >> @@ -946,6 +946,16 @@ map_grant_ref( >> return; >> } >> >> + if ( paging_mode_translate(ld) /* && (op->flags & GNTMAP_host_map) */ && > > I think this wants an explanation in the code why the check is commented. Hmm, in such a case I'd rather omit the commented condition. It being commented has the purpose of documenting itself. Jan _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxxxxxxxxx https://lists.xenproject.org/mailman/listinfo/xen-devel
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