feat(vulkan): enable GPU-based validation for Vulkan backend

If [`VK_LAYER_KHRONOS_validation`] is present, and it supports
[`VK_EXT_validation_features`], we can configure it with another instance
creation info. element of type [`VkValidationFeaturesEXT`] to enable
GPU-based validation. Wire `InstanceFlags::GPU_BASED_VALIDATION` to do
this in the Vulkan backend. It's even already finding issues in our
`examples`! But…we'd like to handle those later. So, I've broken that
out to [a separate issue][examples-fixups].

It is apparent from this and the [DX12 implementation of GPU-based
validation] that we will need to communicate clearly to users that
`InstanceFlags::GPU_BASED_VALIDATION` implies
`InstanceFlags::VALIDATION`. Not all backends enforce this yet; I have
[split out this work][follow-up for flag implication].

Note that `VK_EXT_validation_features` has been deprecated in favor of
the more general layer configuration mechanism offered by
[`VK_EXT_layer_settings`].

[DX12 implementation of GPU-based validation]: #5146
[`VK_EXT_layer_settings`]: https://registry.khronos.org/vulkan/specs/1.3-extensions/man/html/VK_EXT_layer_settings.html
[`VK_EXT_validation_features`]: https://registry.khronos.org/vulkan/specs/1.3-extensions/man/html/VK_EXT_validation_features.html
[`VK_LAYER_KHRONOS_validation`]:https://vulkan.lunarg.com/doc/sdk/1.3.275.0/linux/khronos_validation_layer.html
[`VkValidationFeaturesEXT`]: https://registry.khronos.org/vulkan/specs/1.3-extensions/man/html/VkValidationFeaturesEXT.html
[examples-fixups]: #5231
[follow-up for flag implication]: #5232

CHANGELOG.md

@@ -89,11 +89,11 @@ Bottom level categories:
 - Eager release of GPU resources comes from device.trackers. By @bradwerth in [#5075](https://github.com/gfx-rs/wgpu/pull/5075)
 - `wgpu-types`'s `trace` and `replay` features have been replaced by the `serde` feature. By @KirmesBude in [#5149](https://github.com/gfx-rs/wgpu/pull/5149)
 - `wgpu-core`'s `serial-pass` feature has been removed. Use `serde` instead. By @KirmesBude in [#5149](https://github.com/gfx-rs/wgpu/pull/5149)
-- Added `InstanceFlags::GPU_BASED_VALIDATION`, which enables GPU-based validation for shaders. This is currently only supported on the DX12 back end; other platforms ignore this flag, for now.
+- Added `InstanceFlags::GPU_BASED_VALIDATION`, which enables GPU-based validation for shaders. This is currently only supported on the DX12 and Vulkan backends; other platforms ignore this flag, for now.
   - This has been added to the set of flags set by `InstanceFlags::debugging` and `InstanceFlags::from_build_config`. If you notice your graphics workloads running more slowly, this may be the culprit.
   - As with other instance flags, this flag can be changed in calls to `InstanceFlags::with_env` with the new `WGPU_GPU_BASED_VALIDATION` environment variable.
 
-  By @ErichDonGubler in [#5046](https://github.com/gfx-rs/wgpu/pull/5046).
+  By @ErichDonGubler in [#5146](https://github.com/gfx-rs/wgpu/pull/5146), [#5046](https://github.com/gfx-rs/wgpu/pull/5046).
 - `wgpu::Instance` can now report which `wgpu::Backends` are available based on the build configuration. By @wumpf [#5167](https://github.com/gfx-rs/wgpu/pull/5167)
 ```diff
 -wgpu::Instance::any_backend_feature_enabled()

wgpu-hal/src/vulkan/instance.rs

@@ -653,6 +653,26 @@ impl crate::Instance<super::Api> for super::Instance {
         let validation_layer_name =
             CStr::from_bytes_with_nul(b"VK_LAYER_KHRONOS_validation\0").unwrap();
         let validation_layer_properties = find_layer(&instance_layers, validation_layer_name);
+        let validation_features_are_enabled = || {
+            validation_layer_properties.is_some().then(|| {
+                let exts = Self::enumerate_instance_extension_properties(
+                    &entry,
+                    Some(validation_layer_name),
+                )?;
+                let mut ext_names = exts
+                    .iter()
+                    .filter_map(|ext| cstr_from_bytes_until_nul(&ext.extension_name));
+                let found =
+                    ext_names.any(|ext_name| ext_name == vk::ExtValidationFeaturesFn::name());
+                Ok(found)
+            })
+        };
+        let should_enable_gpu_based_validation = desc
+            .flags
+            .intersects(wgt::InstanceFlags::GPU_BASED_VALIDATION)
+            && validation_features_are_enabled()
+                .transpose()?
+                .unwrap_or(false);
 
         let nv_optimus_layer = CStr::from_bytes_with_nul(b"VK_LAYER_NV_optimus\0").unwrap();
         let has_nv_optimus = find_layer(&instance_layers, nv_optimus_layer).is_some();
@@ -664,7 +684,9 @@ impl crate::Instance<super::Api> for super::Instance {
 
         // Request validation layer if asked.
         let mut debug_utils = None;
-        if desc.flags.intersects(wgt::InstanceFlags::VALIDATION) {
+        if desc.flags.intersects(wgt::InstanceFlags::VALIDATION)
+            || should_enable_gpu_based_validation
+        {
             if let Some(layer_properties) = validation_layer_properties {
                 layers.push(validation_layer_name);
 
@@ -765,6 +787,16 @@ impl crate::Instance<super::Api> for super::Instance {
                 create_info = create_info.push_next(vk_create_info);
             }
 
+            let mut gpu_assisted_validation = vk::ValidationFeaturesEXT::builder()
+                .enabled_validation_features(&[
+                    vk::ValidationFeatureEnableEXT::GPU_ASSISTED,
+                    vk::ValidationFeatureEnableEXT::GPU_ASSISTED_RESERVE_BINDING_SLOT,
+                    vk::ValidationFeatureEnableEXT::SYNCHRONIZATION_VALIDATION,
+                ]);
+            if should_enable_gpu_based_validation {
+                create_info = create_info.push_next(&mut gpu_assisted_validation);
+            }
+
             unsafe {
                 profiling::scope!("vkCreateInstance");
                 entry.create_instance(&create_info, None)

wgpu-types/src/lib.rs

@@ -904,13 +904,15 @@ bitflags::bitflags! {
         /// This mainly applies to a Vulkan driver's compliance version. If the major compliance version
         /// is `0`, then the driver is ignored. This flag allows that driver to be enabled for testing.
         const ALLOW_UNDERLYING_NONCOMPLIANT_ADAPTER = 1 << 3;
-        /// Enable GPU-based validation. Currently, this only changes behavior on the DX12
-        /// backend.
+        /// Enable GPU-based validation. Currently, this only changes behavior on the DX12 and
+        /// Vulkan backends.
         ///
         /// Supported platforms:
         ///
         /// - D3D12; called ["GPU-based validation", or
         ///   "GBV"](https://web.archive.org/web/20230206120404/https://learn.microsoft.com/en-us/windows/win32/direct3d12/using-d3d12-debug-layer-gpu-based-validation)
+        /// - Vulkan, via the `VK_LAYER_KHRONOS_validation` layer; called ["GPU-Assisted
+        ///   Validation"](https://github.com/KhronosGroup/Vulkan-ValidationLayers/blob/e45aeb85079e0835694cb8f03e6681fd18ae72c9/docs/gpu_validation.md#gpu-assisted-validation)
         const GPU_BASED_VALIDATION = 1 << 4;
     }
 }