[Mesa-dev] [PATCH] radv: fix possible GPU hangs by zeroing the descriptor set

[Józef Kucia]

On Fri, Sep 8, 2017 at 2:43 PM, Samuel Pitoiset
<samuel.pitoiset at gmail.com> wrote:
> when an application doesn't update the contents of a descriptor
> set object, it contains random values and this might end up with
> GPU VM faults if a shader tries to access that descriptor.
>
> The Vulkan spec doesn't state what a driver should do when
> a descriptor is unset, but zeroing the contents seems to be
> a safe solution.

FWIW, this is invalid usage. The Vulkan spec states: "Descriptors in
each bound descriptor set, specified via vkCmdBindDescriptorSets, must
be
valid if they are statically used by the currently bound VkPipeline
object, specified via
vkCmdBindPipeline".

>
> This fixes a GPU hang with Unity because a pixel shader tries
> to access a descriptor that is unset by the application.
> Though, maybe that descriptor load should have been DCE'd.
>
> Cc: Pierre-Loup A. Griffais <pgriffais at valvesoftware.com>
> Signed-off-by: Samuel Pitoiset <samuel.pitoiset at gmail.com>
> ---
>  src/amd/vulkan/radv_descriptor_set.c | 6 ++++++
>  1 file changed, 6 insertions(+)
>
> diff --git a/src/amd/vulkan/radv_descriptor_set.c b/src/amd/vulkan/radv_descriptor_set.c
> index 260bfbc12b..6271f9d06e 100644
> --- a/src/amd/vulkan/radv_descriptor_set.c
> +++ b/src/amd/vulkan/radv_descriptor_set.c
> @@ -327,6 +327,12 @@ radv_descriptor_set_create(struct radv_device *device,
>                         list_add(&set->vram_list, prev);
>                 } else
>                         return vk_error(VK_ERROR_OUT_OF_POOL_MEMORY_KHR);
> +
> +               /* Initialize the descriptor set to zero in order to avoid GPU
> +                * VM faults when an application doesn't update the contents of
> +                * a descriptor set object.
> +                */
> +               memset(set->mapped_ptr, 0, layout->size);
>         }
>
>         for (unsigned i = 0; i < layout->binding_count; ++i) {
> --
> 2.14.1
>
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