linux-kernel - Re: "Convert the AMD iommu driver to the dma-iommu api" is buggy

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Date:   Wed, 16 Oct 2019 12:11:27 -0400
From:   Qian Cai <cai@....pw>
To:     Joerg Roedel <jroedel@...e.de>
Cc:     Tom Murphy <murphyt7@....ie>, Robin Murphy <robin.murphy@....com>,
        Christoph Hellwig <hch@....de>,
        iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org
Subject: Re: "Convert the AMD iommu driver to the dma-iommu api" is buggy

On Wed, 2019-10-16 at 18:03 +0200, Joerg Roedel wrote:
> On Wed, Oct 16, 2019 at 11:53:33AM -0400, Qian Cai wrote:
> > On Wed, 2019-10-16 at 17:31 +0200, Joerg Roedel wrote:
> > The x86 one might just be a mistake.
> > 
> > diff --git a/drivers/iommu/amd_iommu.c b/drivers/iommu/amd_iommu.c
> > index ad05484d0c80..63c4b894751d 100644
> > --- a/drivers/iommu/amd_iommu.c
> > +++ b/drivers/iommu/amd_iommu.c
> > @@ -2542,7 +2542,7 @@ static int amd_iommu_map(struct iommu_domain *dom,
> > unsigned long iova,
> >         if (iommu_prot & IOMMU_WRITE)
> >                 prot |= IOMMU_PROT_IW;
> >  
> > -       ret = iommu_map_page(domain, iova, paddr, page_size, prot, GFP_KERNEL);
> > +       ret = iommu_map_page(domain, iova, paddr, page_size, prot, gfp);
> 
> Yeah, that is a bug, I spotted that too.
> 
> > @@ -1185,7 +1185,7 @@ static struct iommu_dma_msi_page
> > *iommu_dma_get_msi_page(struct device *dev,
> >         if (!iova)
> >                 goto out_free_page;
> >  
> > -       if (iommu_map(domain, iova, msi_addr, size, prot))
> > +       if (iommu_map_atomic(domain, iova, msi_addr, size, prot))
> >                 goto out_free_iova;
> 
> Not so sure this is a bug, this code is only about setting up MSIs on
> ARM. It probably doesn't need to be atomic.

The patch "iommu: Add gfp parameter to iommu_ops::map" does this. It could be
called from an atomic context as showed in the arm64 call traces,

+int iommu_map(struct iommu_domain *domain, unsigned long iova,
+             phys_addr_t paddr, size_t size, int prot)
+{
+       might_sleep();
+       return __iommu_map(domain, iova, paddr, size, prot, GFP_KERNEL);
+}