Messages in this thread | | | Date | Wed, 7 Sep 2022 10:05:48 +0100 | Subject | Re: [PATCH v2 1/2] iova: Remove some magazine pointer NULL checks | From | Robin Murphy <> |
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On 2022-09-07 09:46, John Garry wrote: > On 06/09/2022 19:25, Robin Murphy wrote: >>> >>> Caveat: on the chance that the IOVA domain init fails due to the >>> rcache init failing, then, if there were another device in the group >>> which probes later, its probe would be ok as the start_pfn is set. >>> Not Good. >> >> Yeah, there's a lot not to like about iommu_dma_init_domain() - I've >> been banking on it all getting cleaned up when I get to refactoring >> that area of probing (remember the issue you reported years ago with >> PCI groups being built in the wrong order? All related...), but in >> fact since the cookie management got pulled into core code, we can >> probably tie the IOVA domain setup to that right now without much >> other involvement. That could be a cheap win, so I'll give it a go soon. > > ok, great. > > On a related topic, another thing to consider is that errors in IOVA > domain init are not handled gracefully in terms of how we deal with the > device probe and setting dma mapping ops, ref iommu_setup_dma_ops(). I > assume you know all this. > >> >>> - vdpa just fails to create the domain in vduse_domain_create() >>> >>>> That makes a fair amount of sense, but does mean that we're missing >>>> the equivalent in iova_rcache_insert() for it to actually work. Or >>>> we just remove it and tighten up the documentation to say that's not >>>> valid >>> >>> I'd be more inclined to remove it. I would rather remove fathpath >>> checks as much as possible and have robust error handling in the >>> domain init. >>> >>> Afterall I do have the "remove check" craze going. >> >> Sure, like I say I'm happy to be consistent either way. If I do end up >> reinstating such a check I think I'd prefer to have it explicit in >> {alloc,free}_iova_fast() anyway, rather than buried in internal >> implementation details. > > I'm not sure what you would like to see now, if anything. > > I could just remove the iovad->rcache check in iova_rcache_get(). It's > pretty useless (on its own) since we don't have the same check on the > "insert" path.
Yup, just remove it. Sorting iommu-dma is yet another issue, but let's skip straight to fixing that properly by allocating the IOVA domain up-front with the cookie (is this the last remnant of my 7-year-old misunderstanding of dma_32bit_pfn? Let's hope so...)
Thanks, Robin.
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