From: Robin Murphy <robin.murphy@arm.com> To: Christoph Hellwig <hch@infradead.org> Cc: maz@kernel.org, iommu@lists.linux-foundation.org, linux-arm-kernel@lists.infradead.org, Andre Przywara <andre.przywara@arm.com> Subject: Re: [PATCH] iommu/dma: Handle MSI mappings separately Date: Tue, 30 Jul 2019 11:43:25 +0100 [thread overview] Message-ID: <90566814-ed36-2eb9-49e2-98a4a949c9f6@arm.com> (raw) In-Reply-To: <20190730062843.GA1400@infradead.org> On 30/07/2019 07:28, Christoph Hellwig wrote: > On Mon, Jul 29, 2019 at 04:32:38PM +0100, Robin Murphy wrote: >> MSI pages must always be mapped into a device's *current* domain, which >> *might* be the default DMA domain, but might instead be a VFIO domain >> with its own MSI cookie. This subtlety got accidentally lost in the >> streamlining of __iommu_dma_map(), but rather than reintroduce more >> complexity and/or special-casing, it turns out neater to just split this >> path out entirely. >> >> Since iommu_dma_get_msi_page() already duplicates much of what >> __iommu_dma_map() does, it can easily just make the allocation and >> mapping calls directly as well. That way we can further streamline the >> helper back to exclusively operating on DMA domains. >> >> Fixes: b61d271e59d7 ("iommu/dma: Move domain lookup into __iommu_dma_{map,unmap}") >> Reported-by: Shameer Kolothum <shameerali.kolothum.thodi@huawei.com> >> Reported-by: Andre Przywara <andre.przywara@arm.com> >> Signed-off-by: Robin Murphy <robin.murphy@arm.com> > > Hmm. I remember proposing this patch and you didn't like it because > we could also have msis for a !IOMMU_DMA_IOVA_COOKIE cookie type. > Or did we talk past each other? Do you have a pointer? That sparks the vaguest of memories, but I can't seem to turn anything up in my inbox. If that was my objection, though, it sounds like your patch was probably trying to go a step or two further than this one. > Note that if this change turns out to be valid we should also > clean up the iommu_dma_free_iova() side. We're not touching the iommu_dma_{alloc,free}_iova() path here; those are designed to cope with both types of cookie, and I think that's a reasonable abstraction to keep. This is just getting rid of the asymmetry - and now bug - caused by trying to keep the MSI page flow going through a special case in __iommu_dma_map() despite that having evolved into a more specific DMA domain fastpath (there's no corresponding unmap special case since MSI mappings just persist and get recycled until the domain is destroyed). Robin. _______________________________________________ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu
WARNING: multiple messages have this Message-ID (diff)
From: Robin Murphy <robin.murphy@arm.com> To: Christoph Hellwig <hch@infradead.org> Cc: maz@kernel.org, joro@8bytes.org, iommu@lists.linux-foundation.org, linux-arm-kernel@lists.infradead.org, Andre Przywara <andre.przywara@arm.com> Subject: Re: [PATCH] iommu/dma: Handle MSI mappings separately Date: Tue, 30 Jul 2019 11:43:25 +0100 [thread overview] Message-ID: <90566814-ed36-2eb9-49e2-98a4a949c9f6@arm.com> (raw) In-Reply-To: <20190730062843.GA1400@infradead.org> On 30/07/2019 07:28, Christoph Hellwig wrote: > On Mon, Jul 29, 2019 at 04:32:38PM +0100, Robin Murphy wrote: >> MSI pages must always be mapped into a device's *current* domain, which >> *might* be the default DMA domain, but might instead be a VFIO domain >> with its own MSI cookie. This subtlety got accidentally lost in the >> streamlining of __iommu_dma_map(), but rather than reintroduce more >> complexity and/or special-casing, it turns out neater to just split this >> path out entirely. >> >> Since iommu_dma_get_msi_page() already duplicates much of what >> __iommu_dma_map() does, it can easily just make the allocation and >> mapping calls directly as well. That way we can further streamline the >> helper back to exclusively operating on DMA domains. >> >> Fixes: b61d271e59d7 ("iommu/dma: Move domain lookup into __iommu_dma_{map,unmap}") >> Reported-by: Shameer Kolothum <shameerali.kolothum.thodi@huawei.com> >> Reported-by: Andre Przywara <andre.przywara@arm.com> >> Signed-off-by: Robin Murphy <robin.murphy@arm.com> > > Hmm. I remember proposing this patch and you didn't like it because > we could also have msis for a !IOMMU_DMA_IOVA_COOKIE cookie type. > Or did we talk past each other? Do you have a pointer? That sparks the vaguest of memories, but I can't seem to turn anything up in my inbox. If that was my objection, though, it sounds like your patch was probably trying to go a step or two further than this one. > Note that if this change turns out to be valid we should also > clean up the iommu_dma_free_iova() side. We're not touching the iommu_dma_{alloc,free}_iova() path here; those are designed to cope with both types of cookie, and I think that's a reasonable abstraction to keep. This is just getting rid of the asymmetry - and now bug - caused by trying to keep the MSI page flow going through a special case in __iommu_dma_map() despite that having evolved into a more specific DMA domain fastpath (there's no corresponding unmap special case since MSI mappings just persist and get recycled until the domain is destroyed). Robin. _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
next prev parent reply other threads:[~2019-07-30 10:50 UTC|newest] Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top 2019-07-29 15:32 [PATCH] iommu/dma: Handle MSI mappings separately Robin Murphy 2019-07-29 15:32 ` Robin Murphy 2019-07-29 16:03 ` Marc Zyngier 2019-07-29 16:03 ` Marc Zyngier 2019-07-29 16:15 ` Andre Przywara 2019-07-29 16:15 ` Andre Przywara 2019-07-29 16:47 ` Shameerali Kolothum Thodi 2019-07-29 16:47 ` Shameerali Kolothum Thodi 2019-07-30 6:28 ` Christoph Hellwig 2019-07-30 6:28 ` Christoph Hellwig 2019-07-30 10:43 ` Robin Murphy [this message] 2019-07-30 10:43 ` Robin Murphy 2019-07-30 15:06 ` Christoph Hellwig 2019-07-30 15:06 ` Christoph Hellwig 2019-08-06 15:23 ` Joerg Roedel 2019-08-06 15:23 ` Joerg Roedel
Reply instructions: You may reply publicly to this message via plain-text email using any one of the following methods: * Save the following mbox file, import it into your mail client, and reply-to-all from there: mbox Avoid top-posting and favor interleaved quoting: https://en.wikipedia.org/wiki/Posting_style#Interleaved_style * Reply using the --to, --cc, and --in-reply-to switches of git-send-email(1): git send-email \ --in-reply-to=90566814-ed36-2eb9-49e2-98a4a949c9f6@arm.com \ --to=robin.murphy@arm.com \ --cc=andre.przywara@arm.com \ --cc=hch@infradead.org \ --cc=iommu@lists.linux-foundation.org \ --cc=linux-arm-kernel@lists.infradead.org \ --cc=maz@kernel.org \ /path/to/YOUR_REPLY https://kernel.org/pub/software/scm/git/docs/git-send-email.html * If your mail client supports setting the In-Reply-To header via mailto: links, try the mailto: linkBe sure your reply has a Subject: header at the top and a blank line before the message body.
This is an external index of several public inboxes, see mirroring instructions on how to clone and mirror all data and code used by this external index.