From: Robin Murphy <robin.murphy@arm.com> To: Marc Orr <marcorr@google.com>, hch@lst.de, m.szyprowski@samsung.com, jxgao@google.com, iommu@lists.linux-foundation.org, linux-kernel@vger.kernel.org Cc: stable@vger.kernel.org Subject: Re: [PATCH] dma: mark unmapped DMA scatter/gather invalid Date: Mon, 11 Jan 2021 16:08:25 +0000 [thread overview] Message-ID: <dc6db6b4-88f1-4762-bd3b-edf3dd410366@arm.com> (raw) In-Reply-To: <20210111154335.23388-1-marcorr@google.com> On 2021-01-11 15:43, Marc Orr wrote: > This patch updates dma_direct_unmap_sg() to mark each scatter/gather > entry invalid, after it's unmapped. This fixes two issues: s/fixes/bodges around (badly)/ > 1. It makes the unmapping code able to tolerate a double unmap. > 2. It prevents the NVMe driver from erroneously treating an unmapped DMA > address as mapped. > > The bug that motivated this patch was the following sequence, which > occurred within the NVMe driver, with the kernel flag `swiotlb=force`. > > * NVMe driver calls dma_direct_map_sg() > * dma_direct_map_sg() fails part way through the scatter gather/list > * dma_direct_map_sg() calls dma_direct_unmap_sg() to unmap any entries > succeeded. > * NVMe driver calls dma_direct_unmap_sg(), redundantly, leading to a > double unmap, which is a bug. So why not just fix that actual bug? > With this patch, a hadoop workload running on a cluster of three AMD > SEV VMs, is able to succeed. Without the patch, the hadoop workload > suffers application-level and even VM-level failures. > > Tested-by: Jianxiong Gao <jxgao@google.com> > Tested-by: Marc Orr <marcorr@google.com> > Reviewed-by: Jianxiong Gao <jxgao@google.com> > Signed-off-by: Marc Orr <marcorr@google.com> > --- > kernel/dma/direct.c | 4 +++- > 1 file changed, 3 insertions(+), 1 deletion(-) > > diff --git a/kernel/dma/direct.c b/kernel/dma/direct.c > index 0a4881e59aa7..3d9b17fe5771 100644 > --- a/kernel/dma/direct.c > +++ b/kernel/dma/direct.c > @@ -374,9 +374,11 @@ void dma_direct_unmap_sg(struct device *dev, struct scatterlist *sgl, > struct scatterlist *sg; > int i; > > - for_each_sg(sgl, sg, nents, i) > + for_each_sg(sgl, sg, nents, i) { > dma_direct_unmap_page(dev, sg->dma_address, sg_dma_len(sg), dir, > attrs); > + sg->dma_address = DMA_MAPPING_ERROR; There are more DMA API backends than just dma-direct, so while this might help paper over bugs when SWIOTLB is in use, it's not going to have any effect when those same bugs are hit under other circumstances. Once again, the moral of the story is that effort is better spent just fixing the bugs ;) Robin. > + } > } > EXPORT_SYMBOL(dma_direct_unmap_sg); > #endif >
WARNING: multiple messages have this Message-ID (diff)
From: Robin Murphy <robin.murphy@arm.com> To: Marc Orr <marcorr@google.com>, hch@lst.de, m.szyprowski@samsung.com, jxgao@google.com, iommu@lists.linux-foundation.org, linux-kernel@vger.kernel.org Cc: stable@vger.kernel.org Subject: Re: [PATCH] dma: mark unmapped DMA scatter/gather invalid Date: Mon, 11 Jan 2021 16:08:25 +0000 [thread overview] Message-ID: <dc6db6b4-88f1-4762-bd3b-edf3dd410366@arm.com> (raw) In-Reply-To: <20210111154335.23388-1-marcorr@google.com> On 2021-01-11 15:43, Marc Orr wrote: > This patch updates dma_direct_unmap_sg() to mark each scatter/gather > entry invalid, after it's unmapped. This fixes two issues: s/fixes/bodges around (badly)/ > 1. It makes the unmapping code able to tolerate a double unmap. > 2. It prevents the NVMe driver from erroneously treating an unmapped DMA > address as mapped. > > The bug that motivated this patch was the following sequence, which > occurred within the NVMe driver, with the kernel flag `swiotlb=force`. > > * NVMe driver calls dma_direct_map_sg() > * dma_direct_map_sg() fails part way through the scatter gather/list > * dma_direct_map_sg() calls dma_direct_unmap_sg() to unmap any entries > succeeded. > * NVMe driver calls dma_direct_unmap_sg(), redundantly, leading to a > double unmap, which is a bug. So why not just fix that actual bug? > With this patch, a hadoop workload running on a cluster of three AMD > SEV VMs, is able to succeed. Without the patch, the hadoop workload > suffers application-level and even VM-level failures. > > Tested-by: Jianxiong Gao <jxgao@google.com> > Tested-by: Marc Orr <marcorr@google.com> > Reviewed-by: Jianxiong Gao <jxgao@google.com> > Signed-off-by: Marc Orr <marcorr@google.com> > --- > kernel/dma/direct.c | 4 +++- > 1 file changed, 3 insertions(+), 1 deletion(-) > > diff --git a/kernel/dma/direct.c b/kernel/dma/direct.c > index 0a4881e59aa7..3d9b17fe5771 100644 > --- a/kernel/dma/direct.c > +++ b/kernel/dma/direct.c > @@ -374,9 +374,11 @@ void dma_direct_unmap_sg(struct device *dev, struct scatterlist *sgl, > struct scatterlist *sg; > int i; > > - for_each_sg(sgl, sg, nents, i) > + for_each_sg(sgl, sg, nents, i) { > dma_direct_unmap_page(dev, sg->dma_address, sg_dma_len(sg), dir, > attrs); > + sg->dma_address = DMA_MAPPING_ERROR; There are more DMA API backends than just dma-direct, so while this might help paper over bugs when SWIOTLB is in use, it's not going to have any effect when those same bugs are hit under other circumstances. Once again, the moral of the story is that effort is better spent just fixing the bugs ;) Robin. > + } > } > EXPORT_SYMBOL(dma_direct_unmap_sg); > #endif > _______________________________________________ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu
next prev parent reply other threads:[~2021-01-11 16:09 UTC|newest] Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top 2021-01-11 15:43 [PATCH] dma: mark unmapped DMA scatter/gather invalid Marc Orr 2021-01-11 15:43 ` Marc Orr via iommu 2021-01-11 16:08 ` Robin Murphy [this message] 2021-01-11 16:08 ` Robin Murphy 2021-01-11 18:03 ` Marc Orr 2021-01-11 18:03 ` Marc Orr via iommu 2021-01-11 20:39 ` Robin Murphy 2021-01-11 20:39 ` Robin Murphy 2021-01-11 21:36 ` Marc Orr via iommu 2021-01-11 21:36 ` Marc Orr 2021-01-11 16:15 ` Greg KH 2021-01-11 16:15 ` Greg KH
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=dc6db6b4-88f1-4762-bd3b-edf3dd410366@arm.com \ --to=robin.murphy@arm.com \ --cc=hch@lst.de \ --cc=iommu@lists.linux-foundation.org \ --cc=jxgao@google.com \ --cc=linux-kernel@vger.kernel.org \ --cc=m.szyprowski@samsung.com \ --cc=marcorr@google.com \ --cc=stable@vger.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.