Re: [PATCH] drm: add func to better detect wether swiotlb is needed

[Konrad Rzeszutek Wilk]

.snip..
> > -u64 drm_get_max_iomem(void)
> > +bool drm_need_swiotlb(int dma_bits)
> >  {
> > struct resource *tmp;
> > resource_size_t max_iomem = 0;
> > 
> > +   /*
> > +* Xen paravirtual hosts require swiotlb regardless of requested dma
> > +* transfer size.
> > +*
> > +* NOTE: Really, what it requires is use of the dma_alloc_coherent
> > +*   allocator used in ttm_dma_populate() instead of
> > +*   ttm_populate_and_map_pages(), which bounce buffers so much
> > in
> > +*   Xen it leads to swiotlb buffer exhaustion.
> > +*/
> > +   if (xen_pv_domain())
> 
> I've not been following all of the ins and outs of the discussion on this so 
> apologies if I'm missing some context, but...
> 
> This looks like the wrong test to me. I think it should be:
> 
> if ( xen_swiotlb )

Ah, that could be as well. 
> 
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RE: [PATCH] drm: add func to better detect wether swiotlb is needed

[Paul Durrant]

> -Original Message-
> From: Michael D Labriola [mailto:michael.d.labri...@gmail.com]
> Sent: 19 February 2019 23:08
> To: dri-devel@lists.freedesktop.org; Alex Deucher
> ; Christian Koenig ;
> Chunming Zhou ; amd-...@lists.freedesktop.org; Monk
> Liu 
> Cc: Juergen Gross ; Christoph Hellwig
> ; Andrew Cooper ; Paul
> Durrant ; xen-de...@lists.xen.org; Jan Beulich
> ; Konrad Rzeszutek Wilk ;
> Michael D Labriola 
> Subject: [PATCH] drm: add func to better detect wether swiotlb is needed
> 
> This commit fixes DRM failures on Xen PV systems that were introduced in
> v4.17 by the following commits:
> 
> 82626363 drm: add func to get max iomem address v2
> fd5fd480 drm/amdgpu: only enable swiotlb alloc when need v2
> 1bc3d3cc drm/radeon: only enable swiotlb path when need v2
> 
> The introduction of ->need_swiotlb to the ttm_dma_populate() conditionals
> in the radeon and amdgpu device drivers causes Gnome to immediately crash
> on Xen PV systems, returning the user to the login screen.  The following
> kernel errors get logged:
> 
> [   28.554259] radeon_dp_aux_transfer_native: 200 callbacks suppressed
> [   31.219821] radeon :01:00.0: swiotlb buffer is full (sz: 2097152
> bytes)
> [   31.220030] [drm:radeon_gem_object_create [radeon]] *ERROR* Failed to
> allocate GEM object (16384000, 2, 4096, -14)
> [   31.226109] radeon :01:00.0: swiotlb buffer is full (sz: 2097152
> bytes)
> [   31.226300] [drm:radeon_gem_object_create [radeon]] *ERROR* Failed to
> allocate GEM object (16384000, 2, 4096, -14)
> [   31.300734] gnome-shell[1935]: segfault at 88 ip 7f39151cd904 sp
> 7ffc97611ad8 error 4 in libmutter-cogl.so[7f3915178000+aa000]
> [   31.300745] Code: 5f c3 0f 1f 40 00 48 8b 47 78 48 8b 40 40 ff e0 66 0f
> 1f 44 00 00 48 8b 47 78 48 8b 40 48 ff e0 66 0f 1f 44 00 00 48 8b 47 78
> <48> 8b 80 88 00 00 00 ff e0 0f 1f 00 48 8b 47 78 48 8b 40 68 ff e0
> [   38.193302] radeon_dp_aux_transfer_native: 116 callbacks suppressed
> [   40.009317] radeon :01:00.0: swiotlb buffer is full (sz: 2097152
> bytes)
> [   40.009488] [drm:radeon_gem_object_create [radeon]] *ERROR* Failed to
> allocate GEM object (16384000, 2, 4096, -14)
> [   40.015114] radeon :01:00.0: swiotlb buffer is full (sz: 2097152
> bytes)
> [   40.015297] [drm:radeon_gem_object_create [radeon]] *ERROR* Failed to
> allocate GEM object (16384000, 2, 4096, -14)
> [   40.028302] gnome-shell[2431]: segfault at 2dadf40 ip 02dadf40
> sp 7ffcd24ea5f8 error 15
> [   40.028306] Code: 20 6e 31 00 00 00 00 00 00 00 00 37 e3 3d 2d 7f 00 00
> 80 f4 e6 3d 2d 7f 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
> <00> 00 00 00 00 00 00 00 c1 00 00 00 00 00 00 00 80 e1 d2 03 00 00
> 
> This commit renames drm_get_max_iomem() to drm_need_swiotlb(), adds a
> xen_pv_domain() check to it, and moves the bit shifting comparison that
> always follows its usage into the function (simplifying the drm driver
> code).
> 
> Signed-off-by: Michael D Labriola 
> ---
>  drivers/gpu/drm/amd/amdgpu/gmc_v7_0.c  |  2 +-
>  drivers/gpu/drm/amd/amdgpu/gmc_v8_0.c  |  2 +-
>  drivers/gpu/drm/amd/amdgpu/gmc_v9_0.c  |  2 +-
>  drivers/gpu/drm/drm_memory.c   | 19 ---
>  drivers/gpu/drm/radeon/radeon_device.c |  2 +-
>  include/drm/drm_cache.h|  2 +-
>  6 files changed, 21 insertions(+), 8 deletions(-)
> 
> diff --git a/drivers/gpu/drm/amd/amdgpu/gmc_v7_0.c
> b/drivers/gpu/drm/amd/amdgpu/gmc_v7_0.c
> index 910c4ce..6bc0266 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(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 747c068..8638adf 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(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 f35d7a5..4f67093 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));
>