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From: Will Deacon <will@kernel.org>
To: David Stevens <stevensd@chromium.org>
Cc: Robin Murphy <robin.murphy@arm.com>,
	Joerg Roedel <joro@8bytes.org>,
	Lu Baolu <baolu.lu@linux.intel.com>, Tom Murphy <murphyt7@tcd.ie>,
	iommu@lists.linux-foundation.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2 2/4] dma-iommu: fix arch_sync_dma for map with swiotlb
Date: Mon, 2 Aug 2021 14:50:37 +0100	[thread overview]
Message-ID: <20210802135037.GD28547@willie-the-truck> (raw)
In-Reply-To: <20210802134059.GC28547@willie-the-truck>

On Mon, Aug 02, 2021 at 02:40:59PM +0100, Will Deacon wrote:
> On Fri, Jul 09, 2021 at 12:35:00PM +0900, David Stevens wrote:
> > From: David Stevens <stevensd@chromium.org>
> > 
> > When calling arch_sync_dma, we need to pass it the memory that's
> > actually being used for dma. When using swiotlb bounce buffers, this is
> > the bounce buffer. Move arch_sync_dma into the __iommu_dma_map_swiotlb
> > helper, so it can use the bounce buffer address if necessary. This also
> > means it is no longer necessary to call iommu_dma_sync_sg_for_device in
> > iommu_dma_map_sg for untrusted devices.
> > 
> > Fixes: 82612d66d51d ("iommu: Allow the dma-iommu api to use bounce buffers")
> > Signed-off-by: David Stevens <stevensd@chromium.org>
> > ---
> >  drivers/iommu/dma-iommu.c | 16 +++++++---------
> >  1 file changed, 7 insertions(+), 9 deletions(-)
> > 
> > diff --git a/drivers/iommu/dma-iommu.c b/drivers/iommu/dma-iommu.c
> > index eac65302439e..e79e274d2dc5 100644
> > --- a/drivers/iommu/dma-iommu.c
> > +++ b/drivers/iommu/dma-iommu.c
> > @@ -574,6 +574,9 @@ static dma_addr_t __iommu_dma_map_swiotlb(struct device *dev, phys_addr_t phys,
> >  		memset(padding_start, 0, padding_size);
> >  	}
> >  
> > +	if (!coherent && !(attrs & DMA_ATTR_SKIP_CPU_SYNC))
> > +		arch_sync_dma_for_device(phys, org_size, dir);
> 
> I think this relies on the swiotlb buffers residing in the linear mapping
> (i.e. where phys_to_virt() is reliable), which doesn't look like a safe
> assumption to me.

No, sorry, ignore me here. I misread swiotlb_bounce(), so I think your
change is good.

As an aside, it strikes me that we'd probably be better off using
uncacheable bounce buffers for non-coherent devices so we could avoid all
this maintenance entirely.

Will

  reply	other threads:[~2021-08-02 13:56 UTC|newest]

Thread overview: 12+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-07-09  3:34 [PATCH v2 0/4] Fixes for dma-iommu swiotlb bounce buffers David Stevens
2021-07-09  3:34 ` [PATCH v2 1/4] dma-iommu: fix sync_sg with swiotlb David Stevens
2021-08-02 13:30   ` Will Deacon
2021-08-05  3:40     ` David Stevens
2021-07-09  3:35 ` [PATCH v2 2/4] dma-iommu: fix arch_sync_dma for map " David Stevens
2021-08-02 13:40   ` Will Deacon
2021-08-02 13:50     ` Will Deacon [this message]
2021-07-09  3:35 ` [PATCH v2 3/4] dma-iommu: pass SKIP_CPU_SYNC to swiotlb unmap David Stevens
2021-08-02 13:54   ` Will Deacon
2021-08-05  5:26     ` David Stevens
2021-08-06 11:38       ` Will Deacon
2021-07-09  3:35 ` [PATCH v2 4/4] dma-iommu: Check CONFIG_SWIOTLB more broadly David Stevens

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