It's impossible to bind to a host memory which is not coherent.

Hi.

Maybe I'm wrong but when I look into the Allocator implementation I see the following in the Allocator::allocate method:

• If MemoryLocation::CpuToGpu was specified the function tries to find a memory type index for the preferred bits vk::MemoryPropertyFlags::HOST_VISIBLE | vk::MemoryPropertyFlags::HOST_COHERENT | vk::MemoryPropertyFlags::HOST_CACHED.
• If the previous attempt failed the function tries to find a memory type index for the required bits vk::MemoryPropertyFlags::HOST_VISIBLE | vk::MemoryPropertyFlags::HOST_COHERENT.
• If the second attempt fails the function returns Err(AllocationError::NoCompatibleMemoryTypeFound).

So there's no chance to allocate a host visible, non-coherent memory.

Also, in Allocator::new, there's no need to check for host_visible_not_coherent. From the Spec 11.2.1. Device Memory Properties:

There must be at least one memory type with both the VK_MEMORY_PROPERTY_HOST_VISIBLE_BIT and VK_MEMORY_PROPERTY_HOST_COHERENT_BIT bits set in its propertyFlags.

Start in the Allocator::allocate and Allocator::new implementations, tracing the MemoryLocation::CpuToGpu memory-property selection and the host_visible_not_coherent check. Confirm the Vulkan memory-property requirements, then verify that host-visible, non-coherent memory can be selected without breaking the existing compatible-memory error path.