From: "Toke Høiland-Jørgensen" <toke@toke.dk> To: Linus Torvalds <torvalds@linux-foundation.org> Cc: Robin Murphy <robin.murphy@arm.com>, Christoph Hellwig <hch@lst.de>, Maxime Bizon <mbizon@freebox.fr>, Oleksandr Natalenko <oleksandr@natalenko.name>, Halil Pasic <pasic@linux.ibm.com>, Marek Szyprowski <m.szyprowski@samsung.com>, Kalle Valo <kvalo@kernel.org>, "David S. Miller" <davem@davemloft.net>, Jakub Kicinski <kuba@kernel.org>, Paolo Abeni <pabeni@redhat.com>, Olha Cherevyk <olha.cherevyk@gmail.com>, iommu <iommu@lists.linux-foundation.org>, linux-wireless <linux-wireless@vger.kernel.org>, Netdev <netdev@vger.kernel.org>, Linux Kernel Mailing List <linux-kernel@vger.kernel.org>, Greg Kroah-Hartman <gregkh@linuxfoundation.org>, stable <stable@vger.kernel.org> Subject: Re: [REGRESSION] Recent swiotlb DMA_FROM_DEVICE fixes break ath9k-based AP Date: Thu, 24 Mar 2022 22:14:28 +0100 [thread overview] Message-ID: <87r16r834b.fsf@toke.dk> (raw) In-Reply-To: <CAHk-=whUQCCaQXJt3KUeQ8mtnLeVXEScNXCp+_DYh2SNY7EcEA@mail.gmail.com> Linus Torvalds <torvalds@linux-foundation.org> writes: > On Thu, Mar 24, 2022 at 10:07 AM Toke Høiland-Jørgensen <toke@toke.dk> wrote: >> >> Right, but is that sync_for_device call really needed? > > Well, imagine that you have a non-cache-coherent DMA (not bounce > buffers - just bad hardware)... > > So the driver first does that dma_sync_single_for_cpu() for the CPU > see the current state (for the non-cache-coherent case it would just > invalidate caches). > > The driver then examines the command buffer state, sees that it's > still in progress, and does that return -EINPROGRESS. > > It's actually very natural in that situation to flush the caches from > the CPU side again. And so dma_sync_single_for_device() is a fairly > reasonable thing to do in that situation. > > But it doesn't seem *required*, no. The CPU caches only have a copy of > the data in them, no writeback needed (and writeback wouldn't work > since DMA from the device may be in progress). > > So I don't think the dma_sync_single_for_device() is *wrong* per se, > because the CPU didn't actually do any modifications. > > But yes, I think it's unnecessary - because any later CPU accesses > would need that dma_sync_single_for_cpu() anyway, which should > invalidate any stale caches. OK, the above was basically how I understood it. Thank you for confirming! > And it clearly doesn't work in a bounce-buffer situation, but honestly > I don't think a "CPU modified buffers concurrently with DMA" can > *ever* work in that situation, so I think it's wrong for a bounce > buffer model to ever do anything in the dma_sync_single_for_device() > situation. Right. > Does removing that dma_sync_single_for_device() actually fix the > problem for the ath driver? I am hoping Oleksandr can help answer that since my own ath9k hardware is currently on strike :( -Toke
WARNING: multiple messages have this Message-ID (diff)
From: "Toke Høiland-Jørgensen via iommu" <iommu@lists.linux-foundation.org> To: Linus Torvalds <torvalds@linux-foundation.org> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>, Netdev <netdev@vger.kernel.org>, Kalle Valo <kvalo@kernel.org>, linux-wireless <linux-wireless@vger.kernel.org>, Oleksandr Natalenko <oleksandr@natalenko.name>, stable <stable@vger.kernel.org>, "David S. Miller" <davem@davemloft.net>, Halil Pasic <pasic@linux.ibm.com>, iommu <iommu@lists.linux-foundation.org>, Olha Cherevyk <olha.cherevyk@gmail.com>, Jakub Kicinski <kuba@kernel.org>, Maxime Bizon <mbizon@freebox.fr>, Paolo Abeni <pabeni@redhat.com>, Robin Murphy <robin.murphy@arm.com>, Christoph Hellwig <hch@lst.de>, Linux Kernel Mailing List <linux-kernel@vger.kernel.org> Subject: Re: [REGRESSION] Recent swiotlb DMA_FROM_DEVICE fixes break ath9k-based AP Date: Thu, 24 Mar 2022 22:14:28 +0100 [thread overview] Message-ID: <87r16r834b.fsf@toke.dk> (raw) In-Reply-To: <CAHk-=whUQCCaQXJt3KUeQ8mtnLeVXEScNXCp+_DYh2SNY7EcEA@mail.gmail.com> Linus Torvalds <torvalds@linux-foundation.org> writes: > On Thu, Mar 24, 2022 at 10:07 AM Toke Høiland-Jørgensen <toke@toke.dk> wrote: >> >> Right, but is that sync_for_device call really needed? > > Well, imagine that you have a non-cache-coherent DMA (not bounce > buffers - just bad hardware)... > > So the driver first does that dma_sync_single_for_cpu() for the CPU > see the current state (for the non-cache-coherent case it would just > invalidate caches). > > The driver then examines the command buffer state, sees that it's > still in progress, and does that return -EINPROGRESS. > > It's actually very natural in that situation to flush the caches from > the CPU side again. And so dma_sync_single_for_device() is a fairly > reasonable thing to do in that situation. > > But it doesn't seem *required*, no. The CPU caches only have a copy of > the data in them, no writeback needed (and writeback wouldn't work > since DMA from the device may be in progress). > > So I don't think the dma_sync_single_for_device() is *wrong* per se, > because the CPU didn't actually do any modifications. > > But yes, I think it's unnecessary - because any later CPU accesses > would need that dma_sync_single_for_cpu() anyway, which should > invalidate any stale caches. OK, the above was basically how I understood it. Thank you for confirming! > And it clearly doesn't work in a bounce-buffer situation, but honestly > I don't think a "CPU modified buffers concurrently with DMA" can > *ever* work in that situation, so I think it's wrong for a bounce > buffer model to ever do anything in the dma_sync_single_for_device() > situation. Right. > Does removing that dma_sync_single_for_device() actually fix the > problem for the ath driver? I am hoping Oleksandr can help answer that since my own ath9k hardware is currently on strike :( -Toke _______________________________________________ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu
next prev parent reply other threads:[~2022-03-24 21:14 UTC|newest] Thread overview: 139+ messages / expand[flat|nested] mbox.gz Atom feed top 2022-03-23 7:19 [REGRESSION] Recent swiotlb DMA_FROM_DEVICE fixes break ath9k-based AP Oleksandr Natalenko 2022-03-23 7:19 ` Oleksandr Natalenko via iommu 2022-03-23 7:28 ` Kalle Valo 2022-03-23 7:28 ` Kalle Valo 2022-03-23 17:27 ` Linus Torvalds 2022-03-23 17:27 ` Linus Torvalds 2022-03-23 19:06 ` Robin Murphy 2022-03-23 19:06 ` Robin Murphy 2022-03-23 19:16 ` Linus Torvalds 2022-03-23 19:16 ` Linus Torvalds 2022-03-23 20:54 ` Robin Murphy 2022-03-23 20:54 ` Robin Murphy 2022-03-24 5:57 ` Christoph Hellwig 2022-03-24 5:57 ` Christoph Hellwig 2022-03-24 10:25 ` Oleksandr Natalenko 2022-03-24 10:25 ` Oleksandr Natalenko via iommu 2022-03-24 11:05 ` Robin Murphy 2022-03-24 11:05 ` Robin Murphy 2022-03-24 14:27 ` Toke Høiland-Jørgensen 2022-03-24 14:27 ` Toke Høiland-Jørgensen via iommu 2022-03-24 16:29 ` Maxime Bizon 2022-03-24 16:29 ` Maxime Bizon 2022-03-24 16:31 ` Christoph Hellwig 2022-03-24 16:31 ` Christoph Hellwig 2022-03-24 16:52 ` Robin Murphy 2022-03-24 16:52 ` Robin Murphy 2022-03-24 17:07 ` Toke Høiland-Jørgensen 2022-03-24 17:07 ` Toke Høiland-Jørgensen via iommu 2022-03-24 19:26 ` Linus Torvalds 2022-03-24 19:26 ` Linus Torvalds 2022-03-24 21:14 ` Toke Høiland-Jørgensen [this message] 2022-03-24 21:14 ` Toke Høiland-Jørgensen via iommu 2022-03-25 10:25 ` Maxime Bizon 2022-03-25 10:25 ` Maxime Bizon 2022-03-25 11:27 ` Robin Murphy 2022-03-25 11:27 ` Robin Murphy 2022-03-25 23:38 ` Halil Pasic 2022-03-25 23:38 ` Halil Pasic 2022-03-26 16:05 ` Toke Høiland-Jørgensen 2022-03-26 16:05 ` Toke Høiland-Jørgensen via iommu 2022-03-26 18:38 ` Linus Torvalds 2022-03-26 18:38 ` Linus Torvalds 2022-03-26 22:38 ` David Laight 2022-03-26 22:38 ` David Laight 2022-03-26 22:41 ` Linus Torvalds 2022-03-26 22:41 ` Linus Torvalds 2022-03-25 16:25 ` Toke Høiland-Jørgensen 2022-03-25 16:25 ` Toke Høiland-Jørgensen via iommu 2022-03-25 16:45 ` Robin Murphy 2022-03-25 16:45 ` Robin Murphy 2022-03-25 18:13 ` Toke Høiland-Jørgensen via iommu 2022-03-25 18:13 ` Toke Høiland-Jørgensen 2022-03-25 18:30 ` Linus Torvalds 2022-03-25 18:30 ` Linus Torvalds 2022-03-25 19:14 ` Robin Murphy 2022-03-25 19:14 ` Robin Murphy 2022-03-25 19:21 ` Linus Torvalds 2022-03-25 19:21 ` Linus Torvalds 2022-03-25 19:26 ` Oleksandr Natalenko via iommu 2022-03-25 19:26 ` Oleksandr Natalenko 2022-03-25 19:27 ` Linus Torvalds 2022-03-25 19:27 ` Linus Torvalds 2022-03-25 19:35 ` Oleksandr Natalenko via iommu 2022-03-25 19:35 ` Oleksandr Natalenko 2022-03-25 20:37 ` Johannes Berg 2022-03-25 20:37 ` Johannes Berg 2022-03-25 20:47 ` Linus Torvalds 2022-03-25 20:47 ` Linus Torvalds 2022-03-25 21:13 ` Johannes Berg 2022-03-25 21:13 ` Johannes Berg 2022-03-25 21:40 ` David Laight 2022-03-25 21:40 ` David Laight 2022-03-25 21:56 ` Linus Torvalds 2022-03-25 21:56 ` Linus Torvalds 2022-03-25 22:41 ` David Laight 2022-03-25 22:41 ` David Laight 2022-03-27 3:15 ` Halil Pasic 2022-03-27 3:15 ` Halil Pasic 2022-03-28 9:48 ` Johannes Berg 2022-03-28 9:48 ` Johannes Berg 2022-03-28 9:50 ` Johannes Berg 2022-03-28 9:50 ` Johannes Berg 2022-03-28 9:57 ` Johannes Berg 2022-03-28 9:57 ` Johannes Berg 2022-03-27 3:48 ` Halil Pasic 2022-03-27 3:48 ` Halil Pasic 2022-03-27 5:06 ` Linus Torvalds 2022-03-27 5:06 ` Linus Torvalds 2022-03-27 5:21 ` Linus Torvalds 2022-03-27 5:21 ` Linus Torvalds 2022-03-27 15:24 ` David Laight 2022-03-27 15:24 ` David Laight 2022-03-27 19:23 ` Linus Torvalds 2022-03-27 19:23 ` Linus Torvalds 2022-03-27 20:04 ` Linus Torvalds 2022-03-27 20:04 ` Linus Torvalds 2022-03-27 23:52 ` Halil Pasic 2022-03-27 23:52 ` Halil Pasic 2022-03-28 0:30 ` Linus Torvalds 2022-03-28 0:30 ` Linus Torvalds 2022-03-28 12:02 ` Halil Pasic 2022-03-28 12:02 ` Halil Pasic 2022-03-27 23:37 ` Halil Pasic 2022-03-27 23:37 ` Halil Pasic 2022-03-28 0:37 ` Linus Torvalds 2022-03-28 0:37 ` Linus Torvalds 2022-03-25 7:12 ` Oleksandr Natalenko 2022-03-25 7:12 ` Oleksandr Natalenko via iommu 2022-03-25 9:21 ` Thorsten Leemhuis 2022-03-25 9:21 ` Thorsten Leemhuis 2022-03-24 18:31 ` Halil Pasic 2022-03-24 18:31 ` Halil Pasic 2022-03-25 16:31 ` Christoph Hellwig 2022-03-25 16:31 ` Christoph Hellwig 2022-03-24 18:02 ` Halil Pasic 2022-03-24 18:02 ` Halil Pasic 2022-03-25 15:25 ` Halil Pasic 2022-03-25 15:25 ` Halil Pasic 2022-03-25 16:23 ` Robin Murphy 2022-03-25 16:23 ` Robin Murphy 2022-03-25 16:32 ` Christoph Hellwig 2022-03-25 16:32 ` Christoph Hellwig 2022-03-25 18:15 ` Toke Høiland-Jørgensen via iommu 2022-03-25 18:15 ` Toke Høiland-Jørgensen 2022-03-25 18:42 ` Robin Murphy 2022-03-25 18:42 ` Robin Murphy 2022-03-25 18:46 ` Linus Torvalds 2022-03-25 18:46 ` Linus Torvalds 2022-03-28 6:37 ` Christoph Hellwig 2022-03-28 6:37 ` Christoph Hellwig 2022-03-28 8:15 ` David Laight 2022-03-28 8:15 ` David Laight 2022-03-30 12:11 ` Halil Pasic 2022-03-30 12:11 ` Halil Pasic 2022-03-24 8:55 ` Oleksandr Natalenko 2022-03-24 8:55 ` Oleksandr Natalenko via iommu 2022-03-24 12:32 ` [REGRESSION] Recent swiotlb DMA_FROM_DEVICE fixes break ath9k-based AP #forregzbot Thorsten Leemhuis 2022-03-25 9:24 ` Thorsten Leemhuis 2022-03-27 9:00 ` Thorsten Leemhuis
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=87r16r834b.fsf@toke.dk \ --to=toke@toke.dk \ --cc=davem@davemloft.net \ --cc=gregkh@linuxfoundation.org \ --cc=hch@lst.de \ --cc=iommu@lists.linux-foundation.org \ --cc=kuba@kernel.org \ --cc=kvalo@kernel.org \ --cc=linux-kernel@vger.kernel.org \ --cc=linux-wireless@vger.kernel.org \ --cc=m.szyprowski@samsung.com \ --cc=mbizon@freebox.fr \ --cc=netdev@vger.kernel.org \ --cc=oleksandr@natalenko.name \ --cc=olha.cherevyk@gmail.com \ --cc=pabeni@redhat.com \ --cc=pasic@linux.ibm.com \ --cc=robin.murphy@arm.com \ --cc=stable@vger.kernel.org \ --cc=torvalds@linux-foundation.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.