From: Will Deacon <will.deacon-5wv7dgnIgG8@public.gmane.org> To: Robin Murphy <robin.murphy-5wv7dgnIgG8@public.gmane.org> Cc: iommu-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org, tchalamarla-M3mlKVOIwJVv6pq1l3V1OdBPR1lH4CV8@public.gmane.org, brian.starkey-5wv7dgnIgG8@public.gmane.org, linux-arm-kernel-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org Subject: Re: [PATCH 6/7] iommu/arm-smmu: Decouple context format from kernel config Date: Mon, 25 Apr 2016 14:41:08 +0100 [thread overview] Message-ID: <20160425134108.GD30830@arm.com> (raw) In-Reply-To: <571E1851.2030400-5wv7dgnIgG8@public.gmane.org> On Mon, Apr 25, 2016 at 02:14:57PM +0100, Robin Murphy wrote: > On 25/04/16 12:02, Will Deacon wrote: > >In what case would you not have a viable AArch64 granule, but the option > >of falling back to AArch32 makes things work? > > A 4KB page kernel with MMU-401, whose only supported AArch64 granule is > supposedly 64KB. That doesn't sound right at all! > >>Plus we'd have to remove the LPAE page sizes > >>from the bitmap beforehand in the case we don't support AARCH64_4K lest we > >>end up with a phantom format the hardware doesn't actually do, and it all > >>starts getting rather horrible... > > > >I'm not following. The io-pgtable code shouldn't give you back a phanton > >format. > > If you call alloc_io_pgtable_ops() with ARM_64_LPAE_S2 and an unmolested > MMU-401 pgsize_bitmap, you get back a 4K granule v8 pagetable, which per a > strict reading of the TRM isn't supported (although does appear to work in > practice...) I suspect that's a badly worded/incorrect TRM. In reality, I'd be happy to assume that a given granule is supported across all formats (in as much as it can be) if it's supported by one of them, but acknowledge that's not guaranteed by the architecture. > Consider also a stage 1 SMMU supporting all formats but only with 4K > granules: with a 64K page arm64 kernel, the presence of AARCH64_4K support > would lead us into arm_64_lpae_alloc_pgtable_s1(), which would be tricked > into giving us back a 64K granule v8 format by the short descriptor large > page size matching PAGE_SIZE, and things would definitely go downhill from > there. We could improve this by having a separate pgsize_bitmap per format, and passing the relevant one to the relevant page table constructor. > Given that, I think the only truly safe thing to do is to pass an explicit > granule in the io_pgtable_cfg and just get rid of the bitmap-based guessing > in arm_lpae_restrict_pgsizes() - otherwise, we'd still have to pre-restrict > the bitmap, making it pretty much redundant anyway. I'll have a hack at that Actually, I think I prefer to go the other way. Let's try moving more of this common logic into the io-pgtable code. For example, an IOMMU driver could say "I support these formats, and these options (page sizes, quirks, etc) for each format" and the io-pgtable code can choose the most appropriate thing. > - in the meantime please feel free to queue patches 1-3 if you're happy with > them, as that part is still feature-complete without all this context stuff. Queued those, thanks! Will
WARNING: multiple messages have this Message-ID (diff)
From: will.deacon@arm.com (Will Deacon) To: linux-arm-kernel@lists.infradead.org Subject: [PATCH 6/7] iommu/arm-smmu: Decouple context format from kernel config Date: Mon, 25 Apr 2016 14:41:08 +0100 [thread overview] Message-ID: <20160425134108.GD30830@arm.com> (raw) In-Reply-To: <571E1851.2030400@arm.com> On Mon, Apr 25, 2016 at 02:14:57PM +0100, Robin Murphy wrote: > On 25/04/16 12:02, Will Deacon wrote: > >In what case would you not have a viable AArch64 granule, but the option > >of falling back to AArch32 makes things work? > > A 4KB page kernel with MMU-401, whose only supported AArch64 granule is > supposedly 64KB. That doesn't sound right at all! > >>Plus we'd have to remove the LPAE page sizes > >>from the bitmap beforehand in the case we don't support AARCH64_4K lest we > >>end up with a phantom format the hardware doesn't actually do, and it all > >>starts getting rather horrible... > > > >I'm not following. The io-pgtable code shouldn't give you back a phanton > >format. > > If you call alloc_io_pgtable_ops() with ARM_64_LPAE_S2 and an unmolested > MMU-401 pgsize_bitmap, you get back a 4K granule v8 pagetable, which per a > strict reading of the TRM isn't supported (although does appear to work in > practice...) I suspect that's a badly worded/incorrect TRM. In reality, I'd be happy to assume that a given granule is supported across all formats (in as much as it can be) if it's supported by one of them, but acknowledge that's not guaranteed by the architecture. > Consider also a stage 1 SMMU supporting all formats but only with 4K > granules: with a 64K page arm64 kernel, the presence of AARCH64_4K support > would lead us into arm_64_lpae_alloc_pgtable_s1(), which would be tricked > into giving us back a 64K granule v8 format by the short descriptor large > page size matching PAGE_SIZE, and things would definitely go downhill from > there. We could improve this by having a separate pgsize_bitmap per format, and passing the relevant one to the relevant page table constructor. > Given that, I think the only truly safe thing to do is to pass an explicit > granule in the io_pgtable_cfg and just get rid of the bitmap-based guessing > in arm_lpae_restrict_pgsizes() - otherwise, we'd still have to pre-restrict > the bitmap, making it pretty much redundant anyway. I'll have a hack at that Actually, I think I prefer to go the other way. Let's try moving more of this common logic into the io-pgtable code. For example, an IOMMU driver could say "I support these formats, and these options (page sizes, quirks, etc) for each format" and the io-pgtable code can choose the most appropriate thing. > - in the meantime please feel free to queue patches 1-3 if you're happy with > them, as that part is still feature-complete without all this context stuff. Queued those, thanks! Will
next prev parent reply other threads:[~2016-04-25 13:41 UTC|newest] Thread overview: 56+ messages / expand[flat|nested] mbox.gz Atom feed top 2016-04-13 17:12 [PATCH 0/7] arm-smmu: Implementation and context format differentiation Robin Murphy 2016-04-13 17:12 ` Robin Murphy [not found] ` <cover.1460391217.git.robin.murphy-5wv7dgnIgG8@public.gmane.org> 2016-04-13 17:12 ` [PATCH 1/7] iommu/arm-smmu: Differentiate specific implementations Robin Murphy 2016-04-13 17:12 ` Robin Murphy [not found] ` <cc1789284c5efa05514231fa3dede9d1d5f2df18.1460391217.git.robin.murphy-5wv7dgnIgG8@public.gmane.org> 2016-04-13 21:15 ` Chalamarla, Tirumalesh 2016-04-13 21:15 ` Chalamarla, Tirumalesh 2016-04-13 17:12 ` [PATCH 2/7] iommu/arm-smmu: Convert ThunderX workaround to new method Robin Murphy 2016-04-13 17:12 ` Robin Murphy [not found] ` <98b8079ee3ede4427b045214a60ba77f1cb3552c.1460391217.git.robin.murphy-5wv7dgnIgG8@public.gmane.org> 2016-04-13 21:16 ` Chalamarla, Tirumalesh 2016-04-13 21:16 ` Chalamarla, Tirumalesh 2016-04-13 17:12 ` [PATCH 3/7] iommu/arm-smmu: Work around MMU-500 prefetch errata Robin Murphy 2016-04-13 17:12 ` Robin Murphy [not found] ` <0484444b6257bfb6adb68405a72c64fc4fc98142.1460391217.git.robin.murphy-5wv7dgnIgG8@public.gmane.org> 2016-04-21 16:15 ` Will Deacon 2016-04-21 16:15 ` Will Deacon 2016-04-21 16:16 ` Will Deacon 2016-04-21 16:16 ` Will Deacon 2016-04-13 17:13 ` [PATCH 4/7] io-64-nonatomic: Add relaxed accessor variants Robin Murphy 2016-04-13 17:13 ` Robin Murphy [not found] ` <44173fd4e8efd27d670cadc6b30e215243a14099.1460391217.git.robin.murphy-5wv7dgnIgG8@public.gmane.org> 2016-04-21 16:18 ` Will Deacon 2016-04-21 16:18 ` Will Deacon [not found] ` <20160421161859.GK929-5wv7dgnIgG8@public.gmane.org> 2016-04-22 17:08 ` Robin Murphy 2016-04-22 17:08 ` Robin Murphy [not found] ` <571A5A9E.7040305-5wv7dgnIgG8@public.gmane.org> 2016-04-25 13:32 ` Will Deacon 2016-04-25 13:32 ` Will Deacon [not found] ` <20160425133242.GC30830-5wv7dgnIgG8@public.gmane.org> 2016-04-25 15:21 ` Arnd Bergmann 2016-04-25 15:21 ` Arnd Bergmann 2016-04-25 15:28 ` Robin Murphy 2016-04-25 15:28 ` Robin Murphy [not found] ` <571E3781.3070609-5wv7dgnIgG8@public.gmane.org> 2016-04-25 15:41 ` Arnd Bergmann 2016-04-25 15:41 ` Arnd Bergmann 2016-04-25 16:11 ` Will Deacon 2016-04-25 16:11 ` Will Deacon 2016-04-25 16:11 ` Arnd Bergmann 2016-04-25 16:11 ` Arnd Bergmann 2016-04-26 10:38 ` [PATCH v2] " Robin Murphy 2016-04-26 10:38 ` Robin Murphy 2016-04-13 17:13 ` [PATCH 5/7] iommu/arm-smmu: Tidy up 64-bit/atomic I/O accesses Robin Murphy 2016-04-13 17:13 ` Robin Murphy 2016-04-13 17:13 ` [PATCH 6/7] iommu/arm-smmu: Decouple context format from kernel config Robin Murphy 2016-04-13 17:13 ` Robin Murphy [not found] ` <173006777218859d1671ae517c70592c6c02f630.1460391217.git.robin.murphy-5wv7dgnIgG8@public.gmane.org> 2016-04-21 16:30 ` Will Deacon 2016-04-21 16:30 ` Will Deacon [not found] ` <20160421163019.GL929-5wv7dgnIgG8@public.gmane.org> 2016-04-22 17:38 ` Robin Murphy 2016-04-22 17:38 ` Robin Murphy [not found] ` <571A617C.3020102-5wv7dgnIgG8@public.gmane.org> 2016-04-25 11:02 ` Will Deacon 2016-04-25 11:02 ` Will Deacon [not found] ` <20160425110219.GH16065-5wv7dgnIgG8@public.gmane.org> 2016-04-25 13:14 ` Robin Murphy 2016-04-25 13:14 ` Robin Murphy [not found] ` <571E1851.2030400-5wv7dgnIgG8@public.gmane.org> 2016-04-25 13:41 ` Will Deacon [this message] 2016-04-25 13:41 ` Will Deacon [not found] ` <20160425134108.GD30830-5wv7dgnIgG8@public.gmane.org> 2016-04-25 16:21 ` Robin Murphy 2016-04-25 16:21 ` Robin Murphy 2016-04-28 16:12 ` [PATCH v2] " Robin Murphy 2016-04-28 16:12 ` Robin Murphy 2016-04-13 17:13 ` [PATCH 7/7] iommu/arm-smmu: Support SMMUv1 64KB supplement Robin Murphy 2016-04-13 17:13 ` Robin Murphy
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=20160425134108.GD30830@arm.com \ --to=will.deacon-5wv7dgnigg8@public.gmane.org \ --cc=brian.starkey-5wv7dgnIgG8@public.gmane.org \ --cc=iommu-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org \ --cc=linux-arm-kernel-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org \ --cc=robin.murphy-5wv7dgnIgG8@public.gmane.org \ --cc=tchalamarla-M3mlKVOIwJVv6pq1l3V1OdBPR1lH4CV8@public.gmane.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.