Unexpected VUID-VkSubpassDescription2-externalFormatResolve-09338 in some CTS tests

[rg3igalia]

Environment:

• OS: Fedora Linux 43
• GPU and driver version: lavapipe from Mesa main
• SDK or header version if building from repo: 430c8b9
• Options enabled (synchronization, best practices, etc.): defaults + synchronization

Describe the Issue

In internal CTS issue 6230, @spencer-lunarg reported that tests such as:

dEQP-VK.pipeline.monolithic.multisample.multisampled_render_to_single_sampled.multi_subpass.r8g8b8a8_unorm_r16g16b16a16_sfloat_r32g32b32a32_uint_d16_unorm.random_64

Make the layers report VUID-VkSubpassDescription2-externalFormatResolve-09338, which is true as of today as far as I can see. After analyzing the issue, I think the layers are wrong here.

VUID-VkSubpassDescription2-externalFormatResolve-09338 reads:

If the externalFormatResolve feature is not enabled and pResolveAttachments is not NULL, for each resolve attachment that is not VK_ATTACHMENT_UNUSED, the corresponding color attachment must not have a sample count of VK_SAMPLE_COUNT_1_BIT

Which is pretty simple: if you're resolving, the original color attachment must not be single-sample already.

The test contains a render pass with 3 subpasses, and the layers appear to be complaining about subpass 0, for example. Some info about the render pass setup:

Attachment descriptions:

Index	Format	Samples
0	VK_FORMAT_R8G8B8A8_UNORM	1
1	VK_FORMAT_R16G16B16A16_SFLOAT	8
2	VK_FORMAT_R32G32B32A32_UINT	8
3	VK_FORMAT_D16_UNORM	1
4	VK_FORMAT_R16G16B16A16_SFLOAT	1
5	VK_FORMAT_R32G32B32A32_UINT	1

Subpass 0:

• Color attachments: 2, unused, 0, 1, 3
• Resolve attachments: 5, unused, unused, unused, unused

As we can see, the only attachment that is resolved is the one at color location 0 in the subpass, which resolves attachment 2 (8 samples) into attachment 5 (1 sample, same format). Other resolve attachments are unused, so I'm not sure why the layers report the VUID.

Expected behavior

No validation errors.

Valid Usage ID

VUID-VkSubpassDescription2-externalFormatResolve-09338

ERROR|VALIDATION: [VUID-VkSubpassDescription2-externalFormatResolve-09338] vkCreateRenderPass2(): pCreateInfo->pAttachments[0].samples is VK_SAMPLE_COUNT_1_BIT.
The Vulkan spec states: If the externalFormatResolve feature is not enabled and pResolveAttachments is not NULL, for each resolve attachment that is not VK_ATTACHMENT_UNUSED, the corresponding color attachment must not have a sample count of VK_SAMPLE_COUNT_1_BIT (https://docs.vulkan.org/spec/latest/chapters/renderpass.html#VUID-VkSubpassDescription2-externalFormatResolve-09338)

Additional context

N/A