linux-kernel - Re: [PATCH V2 5/5] DO NOT MERGE: iommu: disable list appending in dma-iommu

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Date:   Wed, 9 Sep 2020 09:43:09 +0800
From:   Lu Baolu <baolu.lu@...ux.intel.com>
To:     Christoph Hellwig <hch@...radead.org>
Cc:     baolu.lu@...ux.intel.com, Tom Murphy <murphyt7@....ie>,
        intel-gfx@...ts.freedesktop.org,
        Joonas Lahtinen <joonas.lahtinen@...ux.intel.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Jani Nikula <jani.nikula@...ux.intel.com>,
        iommu@...ts.linux-foundation.org,
        Rodrigo Vivi <rodrigo.vivi@...el.com>,
        David Woodhouse <dwmw2@...radead.org>
Subject: Re: [PATCH V2 5/5] DO NOT MERGE: iommu: disable list appending in
 dma-iommu

Hi Christoph,

On 9/8/20 2:23 PM, Christoph Hellwig wrote:
> On Tue, Sep 08, 2020 at 02:04:53PM +0800, Lu Baolu wrote:
>> Do you mind telling where can I find Marek's series?
> 
> [PATCH v10 00/30] DRM: fix struct sg_table nents vs. orig_nents misuse
> 
> on various lists including the iommu one.
> 

It seems that more work is needed in i915 driver. I will added below
quirk as you suggested.

--- a/drivers/iommu/dma-iommu.c
+++ b/drivers/iommu/dma-iommu.c
@@ -851,6 +851,31 @@ static int __finalise_sg(struct device *dev, struct 
scatterlist *sg, int nents,
         unsigned int cur_len = 0, max_len = dma_get_max_seg_size(dev);
         int i, count = 0;

+       /*
+        * The Intel graphic device driver is used to assume that the 
returned
+        * sg list is not combound. This blocks the efforts of 
converting the
+        * Intel IOMMU driver to dma-iommu api's. Add this quirk to make the
+        * device driver work and should be removed once it's fixed in i915
+        * driver.
+        */
+       if (dev_is_pci(dev) &&
+           to_pci_dev(dev)->vendor == PCI_VENDOR_ID_INTEL &&
+           (to_pci_dev(dev)->class >> 16) == PCI_BASE_CLASS_DISPLAY) {
+               for_each_sg(sg, s, nents, i) {
+                       unsigned int s_iova_off = sg_dma_address(s);
+                       unsigned int s_length = sg_dma_len(s);
+                       unsigned int s_iova_len = s->length;
+
+                       s->offset += s_iova_off;
+                       s->length = s_length;
+                       sg_dma_address(s) = dma_addr + s_iova_off;
+                       sg_dma_len(s) = s_length;
+                       dma_addr += s_iova_len;
+               }
+
+               return nents;
+       }
+

Best regards,
baolu