linux-kernel - Re: [RFC 1/7] iommu/vt-d: Set the dma_ops per device so we can remove the iommu_no

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Date:   Mon, 6 May 2019 16:27:09 +0100
From:   Tom Murphy <tmurphy@...sta.com>
To:     Lu Baolu <baolu.lu@...ux.intel.com>
Cc:     iommu@...ts.linux-foundation.org, Tom Murphy <murphyt7@....ie>,
        Joerg Roedel <joro@...tes.org>,
        Will Deacon <will.deacon@....com>,
        Robin Murphy <robin.murphy@....com>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        Kukjin Kim <kgene@...nel.org>,
        Krzysztof Kozlowski <krzk@...nel.org>,
        David Woodhouse <dwmw2@...radead.org>,
        Andy Gross <andy.gross@...aro.org>,
        David Brown <david.brown@...aro.org>,
        Matthias Brugger <matthias.bgg@...il.com>,
        Rob Clark <robdclark@...il.com>,
        Heiko Stuebner <heiko@...ech.de>,
        Gerald Schaefer <gerald.schaefer@...ibm.com>,
        Thierry Reding <thierry.reding@...il.com>,
        Jonathan Hunter <jonathanh@...dia.com>,
        Alex Williamson <alex.williamson@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Marc Zyngier <marc.zyngier@....com>,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-samsung-soc@...r.kernel.org, linux-arm-msm@...r.kernel.org,
        linux-mediatek@...ts.infradead.org,
        linux-rockchip@...ts.infradead.org, linux-s390@...r.kernel.org,
        linux-tegra@...r.kernel.org, kvm@...r.kernel.org
Subject: Re: [RFC 1/7] iommu/vt-d: Set the dma_ops per device so we can remove
 the iommu_no_mapping code

On Mon, May 6, 2019 at 2:48 AM Lu Baolu <baolu.lu@...ux.intel.com> wrote:
>
> Hi,
>
> On 5/4/19 9:23 PM, Tom Murphy wrote:
> > Set the dma_ops per device so we can remove the iommu_no_mapping code.
> >
> > Signed-off-by: Tom Murphy<tmurphy@...sta.com>
> > ---
> >   drivers/iommu/intel-iommu.c | 85 +++----------------------------------
> >   1 file changed, 6 insertions(+), 79 deletions(-)
> >
> > diff --git a/drivers/iommu/intel-iommu.c b/drivers/iommu/intel-iommu.c
> > index eace915602f0..2db1dc47e7e4 100644
> > --- a/drivers/iommu/intel-iommu.c
> > +++ b/drivers/iommu/intel-iommu.c
> > @@ -2622,17 +2622,6 @@ static int __init si_domain_init(int hw)
> >       return 0;
> >   }
> >
> > -static int identity_mapping(struct device *dev)
> > -{
> > -     struct device_domain_info *info;
> > -
> > -     info = dev->archdata.iommu;
> > -     if (info && info != DUMMY_DEVICE_DOMAIN_INFO)
> > -             return (info->domain == si_domain);
> > -
> > -     return 0;
> > -}
> > -
> >   static int domain_add_dev_info(struct dmar_domain *domain, struct device *dev)
> >   {
> >       struct dmar_domain *ndomain;
> > @@ -3270,43 +3259,6 @@ static unsigned long intel_alloc_iova(struct device *dev,
> >       return iova_pfn;
> >   }
> >
> > -/* Check if the dev needs to go through non-identity map and unmap process.*/
> > -static int iommu_no_mapping(struct device *dev)
> > -{
> > -     int found;
> > -
> > -     if (iommu_dummy(dev))
> > -             return 1;
> > -
> > -     found = identity_mapping(dev);
> > -     if (found) {
> > -             /*
> > -              * If the device's dma_mask is less than the system's memory
> > -              * size then this is not a candidate for identity mapping.
> > -              */
> > -             u64 dma_mask = *dev->dma_mask;
> > -
> > -             if (dev->coherent_dma_mask &&
> > -                 dev->coherent_dma_mask < dma_mask)
> > -                     dma_mask = dev->coherent_dma_mask;
> > -
> > -             if (dma_mask < dma_get_required_mask(dev)) {
> > -                     /*
> > -                      * 32 bit DMA is removed from si_domain and fall back
> > -                      * to non-identity mapping.
> > -                      */
> > -                     dmar_remove_one_dev_info(dev);
> > -                     dev_warn(dev, "32bit DMA uses non-identity mapping\n");
> > -
> > -                     return 0;
> > -             }
>
> The iommu_no_mapping() also checks whether any 32bit DMA device uses
> identity mapping. The device might not work if the system memory space
> is bigger than 4G.

It looks like their is actually a bug in the v3 of the "iommu/vt-d:
Delegate DMA domain to generic iommu" patch set. I will leave a
message in that email thread. Fixing that bug should also fix this
issue.


>
> Will you add this to other place, or it's unnecessary?
>
> Best regards,
> Lu Baolu