Messages in this thread | | | Date | Tue, 6 Sep 2022 14:37:18 +0100 | Subject | Re: [PATCH v2 1/2] iova: Remove some magazine pointer NULL checks | From | Robin Murphy <> |
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On 2022-09-06 11:50, John Garry wrote: > On 06/09/2022 10:28, Ethan Zhao wrote: > > Hi Ethan, > >>> Signed-off-by: John Garry <john.garry@huawei.com> >>> Reviewed-by: Robin Murphy <robin.murphy@arm.com> >>> --- >>> drivers/iommu/iova.c | 7 ++----- >>> 1 file changed, 2 insertions(+), 5 deletions(-) >>> >>> diff --git a/drivers/iommu/iova.c b/drivers/iommu/iova.c >>> index 47d1983dfa2a..580fdf669922 100644 >>> --- a/drivers/iommu/iova.c >>> +++ b/drivers/iommu/iova.c >>> @@ -661,9 +661,6 @@ iova_magazine_free_pfns(struct iova_magazine >>> *mag, struct iova_domain *iovad) >>> unsigned long flags; >>> int i; >>> - if (!mag) >>> - return; >>> - >> >> iommu_probe_device >> ops->probe_finalize(dev); >> intel_iommu_probe_finalize >> iommu_setup_dma_ops >> iommu_dma_init_domain(domain, dma_base, dma_limit, dev) >> iova_domain_init_rcaches >> { >> ... >> cpu_rcache->loaded = iova_magazine_alloc(GFP_KERNEL); >> cpu_rcache->prev = iova_magazine_alloc(GFP_KERNEL); >> if (!cpu_rcache->loaded || !cpu_rcache->prev) { >> ret = -ENOMEM; >> goto out_err; >> >> Do you mean iova_magazine_alloc() is impossible to fail ? > > No, iova_magazine_alloc() may fail and return NULL. But if it does then > we set iovad rcache pointer = NULL in the error path and don't use the > rcache. > > However we have a !iovad->rcache check on the "fast" alloc but not > "insert". I need to check why that is again.
Right, if you find a good reason to respin the patch then perhaps also tweaking the commit message to clarify that it's impossible to have a NULL rcache *at any point where those checks are made* might avoid all possible doubt, however I'd hope that it's clear enough that the transient case while iova_domain_init_rcaches() is in the process of failing really doesn't need consideration in its own right.
I guess the check in iova_rcache_get() was maybe with the intent of allowing alloc_iova_fast() to seamlessly fall back to standard allocation, so an API user can treat iova_domain_init_rcaches() failure as non-fatal? 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 would like a way to make rcaches optional in iommu-dma for systems where they're a pointless waste of memory, but we can always revisit this when we get there.
Cheers, Robin.
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