Well adding write support is trivial.

What I'm more concerned about is if setting page->mapping during allocation of the page could have any negative effect?

I of hand don't see any since the page isn't reclaimable directly anyway, but I'm not 100% sure of that.

Christian.

Am 05.02.2018 um 12:49 schrieb Tom St Denis:
Another thing that occurred to me is this will break write access to GPU bound memory.  Previously we relied on iova to translate the address and then /dev/mem or /dev/fmem to read/write it.  But since this is literally a read only method obviously there's no write support.

Tom


On 04/02/18 09:56 PM, He, Roger wrote:
Patch1 & 2 & 4,   Reviewed-by: Roger He <hongbo...@amd.com>
Patch 5:  Acked-by: Roger He <hongbo...@amd.com>

-----Original Message-----
From: dri-devel [mailto:dri-devel-boun...@lists.freedesktop.org] On Behalf Of Christian K?nig
Sent: Saturday, February 03, 2018 3:10 AM
To: amd-...@lists.freedesktop.org; dri-devel@lists.freedesktop.org
Subject: [PATCH 5/5] drm/amdgpu: replace iova debugfs file with iomem

This allows access to pages allocated through the driver with optional IOMMU mapping.

Signed-off-by: Christian König <christian.koe...@amd.com>
---
  drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c | 57 ++++++++++++++++++++-------------
  1 file changed, 35 insertions(+), 22 deletions(-)

diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c
index 648c449aaa79..795ceaeb82d5 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c
@@ -1929,38 +1929,51 @@ static const struct file_operations amdgpu_ttm_gtt_fops = {
    #endif
  -static ssize_t amdgpu_iova_to_phys_read(struct file *f, char __user *buf,
-                   size_t size, loff_t *pos)
+static ssize_t amdgpu_iomem_read(struct file *f, char __user *buf,
+                 size_t size, loff_t *pos)
  {
      struct amdgpu_device *adev = file_inode(f)->i_private;
-    int r;
-    uint64_t phys;
      struct iommu_domain *dom;
+    ssize_t result = 0;
+    int r;
  -    // always return 8 bytes
-    if (size != 8)
-        return -EINVAL;
+    dom = iommu_get_domain_for_dev(adev->dev);
  -    // only accept page addresses
-    if (*pos & 0xFFF)
-        return -EINVAL;
+    while (size) {
+        phys_addr_t addr = *pos & PAGE_MASK;
+        loff_t off = *pos & ~PAGE_MASK;
+        size_t bytes = PAGE_SIZE - off;
+        unsigned long pfn;
+        struct page *p;
+        void *ptr;
  -    dom = iommu_get_domain_for_dev(adev->dev);
-    if (dom)
-        phys = iommu_iova_to_phys(dom, *pos);
-    else
-        phys = *pos;
+        addr = dom ? iommu_iova_to_phys(dom, addr) : addr;
  -    r = copy_to_user(buf, &phys, 8);
-    if (r)
-        return -EFAULT;
+        pfn = addr >> PAGE_SHIFT;
+        if (!pfn_valid(pfn))
+            return -EPERM;
+
+        p = pfn_to_page(pfn);
+        if (p->mapping != adev->mman.bdev.dev_mapping)
+            return -EPERM;
+
+        ptr = kmap(p);
+        r = copy_to_user(buf, ptr, bytes);
+        kunmap(p);
+        if (r)
+            return -EFAULT;
  -    return 8;
+        size -= bytes;
+        *pos += bytes;
+        result += bytes;
+    }
+
+    return result;
  }
  -static const struct file_operations amdgpu_ttm_iova_fops = {
+static const struct file_operations amdgpu_ttm_iomem_fops = {
      .owner = THIS_MODULE,
-    .read = amdgpu_iova_to_phys_read,
+    .read = amdgpu_iomem_read,
      .llseek = default_llseek
  };
  @@ -1973,7 +1986,7 @@ static const struct {  #ifdef CONFIG_DRM_AMDGPU_GART_DEBUGFS
      { "amdgpu_gtt", &amdgpu_ttm_gtt_fops, TTM_PL_TT }, #endif
-    { "amdgpu_iova", &amdgpu_ttm_iova_fops, TTM_PL_SYSTEM },
+    { "amdgpu_iomem", &amdgpu_ttm_iomem_fops, TTM_PL_SYSTEM },
  };
    #endif
--
2.14.1

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