Re: [Xen-devel] Upstream Dom0 DRM problems regarding swiotlb

[Michael Labriola <michael.d.labriola@xxxxxxxxx>]

On Wed, Feb 13, 2019 at 1:16 PM Michael Labriola
<michael.d.labriola@xxxxxxxxx> wrote:
>
> On Wed, Feb 13, 2019 at 11:57 AM Konrad Rzeszutek Wilk
> <konrad.wilk@xxxxxxxxxx> wrote:
> >
> > On Wed, Feb 13, 2019 at 09:09:32AM -0700, Jan Beulich wrote:
> > > >>> On 13.02.19 at 17:00, <michael.d.labriola@xxxxxxxxx> wrote:
> > > > On Wed, Feb 13, 2019 at 9:28 AM Jan Beulich <JBeulich@xxxxxxxx> wrote:
> > > >> >>> On 13.02.19 at 15:10, <michael.d.labriola@xxxxxxxxx> wrote:
> > > >> > Ah, so this isn't necessarily Xen-specific but rather any paravirtual
> > > >> > guest?  That hadn't crossed my mind.  Is there an easy way to find 
> > > >> > out
> > > >> > if we're a pv guest in the need_swiotlb conditionals?
> > > >>
> > > >> There's xen_pv_domain(), but I think xen_swiotlb would be more to
> > > >> the point if the check is already to be Xen-specific. There's no 
> > > >> generic
> > > >> "is PV" predicate that I'm aware of.
> > > >
> > > > Well, that makes doing conditional code right more difficult.  I
> > > > assume since there isn't a generic predicate, and PV isn't new, that
> > > > it's absence is by design?  To reign in the temptation to sprinkle
> > > > conditional code all over the kernel?  ;-)
> > >
> > > Well, with lguest gone, Xen is the only PV environment the kernel
> > > can run in, afaik at least. I guess to decide between the suggested
> > > options or the need for some abstracting macro (or yet something
> > > else), you'll really need to ask the driver maintainers. Or simply
> > > send a patch their way implementing one of them, and see what
> > > their reaction is.
> >
> > Could you try this out and see if it works and I will send it out:
> >
*snip*
>
> Yes, that works for me.  However, I feel like the conditional should
> be in drm_get_max_iomem() instead of directly after it everywhere it's
> used...  and is just checking xen_pv_domain() enough?  Jan made it
> sound like there were possibly other PV cases that would also still
> need swiotlb.

How about this?  It strcmp's pv_info to see if we're bare metal, does
the comparison in a single place, moves the bit shifting comparison
into the function (simplifying the drm driver code), and renames the
function to more aptly describe what's going on.


diff --git a/drivers/gpu/drm/amd/amdgpu/gmc_v6_0.c
b/drivers/gpu/drm/amd/amdgpu/gmc_v6_0.c
index 73ad02aea2b2..328d45b8b2ec 100644
--- a/drivers/gpu/drm/amd/amdgpu/gmc_v6_0.c
+++ b/drivers/gpu/drm/amd/amdgpu/gmc_v6_0.c
@@ -885,7 +885,7 @@ static int gmc_v6_0_sw_init(void *handle)
         pci_set_consistent_dma_mask(adev->pdev, DMA_BIT_MASK(32));
         dev_warn(adev->dev, "amdgpu: No coherent DMA available.\n");
     }
-    adev->need_swiotlb = drm_get_max_iomem() > ((u64)1 << dma_bits);
+    adev->need_swiotlb = drm_need_swiotlb_for_dma(dma_bits);

     r = gmc_v6_0_init_microcode(adev);
     if (r) {
diff --git a/drivers/gpu/drm/amd/amdgpu/gmc_v7_0.c
b/drivers/gpu/drm/amd/amdgpu/gmc_v7_0.c
index 910c4ce19cb3..3d49eff28448 100644
--- a/drivers/gpu/drm/amd/amdgpu/gmc_v7_0.c
+++ b/drivers/gpu/drm/amd/amdgpu/gmc_v7_0.c
@@ -1029,7 +1029,7 @@ static int gmc_v7_0_sw_init(void *handle)
         pci_set_consistent_dma_mask(adev->pdev, DMA_BIT_MASK(32));
         pr_warn("amdgpu: No coherent DMA available\n");
     }
-    adev->need_swiotlb = drm_get_max_iomem() > ((u64)1 << dma_bits);
+    adev->need_swiotlb = drm_need_swiotlb_for_dma(dma_bits);

     r = gmc_v7_0_init_microcode(adev);
     if (r) {
diff --git a/drivers/gpu/drm/amd/amdgpu/gmc_v8_0.c
b/drivers/gpu/drm/amd/amdgpu/gmc_v8_0.c
index 747c068379dc..9247dd6316f1 100644
--- a/drivers/gpu/drm/amd/amdgpu/gmc_v8_0.c
+++ b/drivers/gpu/drm/amd/amdgpu/gmc_v8_0.c
@@ -1155,7 +1155,7 @@ static int gmc_v8_0_sw_init(void *handle)
         pci_set_consistent_dma_mask(adev->pdev, DMA_BIT_MASK(32));
         pr_warn("amdgpu: No coherent DMA available\n");
     }
-    adev->need_swiotlb = drm_get_max_iomem() > ((u64)1 << dma_bits);
+    adev->need_swiotlb = drm_need_swiotlb_for_dma(dma_bits);

     r = gmc_v8_0_init_microcode(adev);
     if (r) {
diff --git a/drivers/gpu/drm/amd/amdgpu/gmc_v9_0.c
b/drivers/gpu/drm/amd/amdgpu/gmc_v9_0.c
index f35d7a554ad5..89f3fe981ac5 100644
--- a/drivers/gpu/drm/amd/amdgpu/gmc_v9_0.c
+++ b/drivers/gpu/drm/amd/amdgpu/gmc_v9_0.c
@@ -989,7 +989,7 @@ static int gmc_v9_0_sw_init(void *handle)
         pci_set_consistent_dma_mask(adev->pdev, DMA_BIT_MASK(32));
         printk(KERN_WARNING "amdgpu: No coherent DMA available.\n");
     }
-    adev->need_swiotlb = drm_get_max_iomem() > ((u64)1 << dma_bits);
+    adev->need_swiotlb = drm_need_swiotlb_for_dma(dma_bits);

     if (adev->asic_type == CHIP_VEGA20) {
         r = gfxhub_v1_1_get_xgmi_info(adev);
diff --git a/drivers/gpu/drm/drm_memory.c b/drivers/gpu/drm/drm_memory.c
index d69e4fc1ee77..f22f6a0d20b3 100644
--- a/drivers/gpu/drm/drm_memory.c
+++ b/drivers/gpu/drm/drm_memory.c
@@ -35,6 +35,7 @@

 #include <linux/highmem.h>
 #include <linux/export.h>
+#include <xen/xen.h>
 #include <drm/drmP.h>
 #include "drm_legacy.h"

@@ -150,15 +151,24 @@ void drm_legacy_ioremapfree(struct drm_local_map
*map, struct drm_device *dev)
 }
 EXPORT_SYMBOL(drm_legacy_ioremapfree);

-u64 drm_get_max_iomem(void)
+bool drm_need_swiotlb_for_dma(int dma_bits)
 {
     struct resource *tmp;
     resource_size_t max_iomem = 0;

+#ifdef CONFIG_PARAVIRT
+    /*
+     * Paravirtual hosts require swiotlb regardless of requested dma
+     * transfer size.
+     */
+    if (strcmp(pv_info.name, "bare hardware") != 0)
+        return true;
+#endif
+
     for (tmp = iomem_resource.child; tmp; tmp = tmp->sibling) {
         max_iomem = max(max_iomem,  tmp->end);
     }

-    return max_iomem;
+    return max_iomem > ((u64)1 << dma_bits);
 }
-EXPORT_SYMBOL(drm_get_max_iomem);
+EXPORT_SYMBOL(drm_need_swiotlb_for_dma);
diff --git a/drivers/gpu/drm/radeon/radeon_device.c
b/drivers/gpu/drm/radeon/radeon_device.c
index 59c8a6647ff2..7c8222d98bc3 100644
--- a/drivers/gpu/drm/radeon/radeon_device.c
+++ b/drivers/gpu/drm/radeon/radeon_device.c
@@ -1387,7 +1387,8 @@ int radeon_device_init(struct radeon_device *rdev,
         pci_set_consistent_dma_mask(rdev->pdev, DMA_BIT_MASK(32));
         pr_warn("radeon: No coherent DMA available\n");
     }
-    rdev->need_swiotlb = drm_get_max_iomem() > ((u64)1 << dma_bits);
+    rdev->need_swiotlb = drm_need_swiotlb_for_dma(dma_bits);
+    pr_info("%s: need_swiotlb: %d\n", __func__, rdev->need_swiotlb);

     /* Registers mapping */
     /* TODO: block userspace mapping of io register */
diff --git a/include/drm/drm_cache.h b/include/drm/drm_cache.h
index bfe1639df02d..070b44624ff9 100644
--- a/include/drm/drm_cache.h
+++ b/include/drm/drm_cache.h
@@ -38,7 +38,7 @@
 void drm_clflush_pages(struct page *pages[], unsigned long num_pages);
 void drm_clflush_sg(struct sg_table *st);
 void drm_clflush_virt_range(void *addr, unsigned long length);
-u64 drm_get_max_iomem(void);
+bool drm_need_swiotlb_for_dma(int dma_bits);


 static inline bool drm_arch_can_wc_memory(void)

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