Re: [RFC V1 1/5] swiotlb: Support allocating DMA memory from SWIOTLB
From: Kirill A. Shutemov
Date: Wed Feb 14 2024 - 09:50:10 EST
On Fri, Jan 12, 2024 at 05:52:47AM +0000, Vishal Annapurve wrote:
> Modify SWIOTLB framework to allocate DMA memory always from SWIOTLB.
>
> CVMs use SWIOTLB buffers for bouncing memory when using dma_map_* APIs
> to setup memory for IO operations. SWIOTLB buffers are marked as shared
> once during early boot.
>
> Buffers allocated using dma_alloc_* APIs are allocated from kernel memory
> and then converted to shared during each API invocation. This patch ensures
> that such buffers are also allocated from already shared SWIOTLB
> regions. This allows enforcing alignment requirements on regions marked
> as shared.
But does it work in practice?
Some devices (like GPUs) require a lot of DMA memory. So with this approach
we would need to have huge SWIOTLB buffer that is unused in most VMs.
--
Kiryl Shutsemau / Kirill A. Shutemov