linux-kernel - Re: [PATCH 06/16] iommu/dma: use page allocation function provided by iommu-pages.h

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Message-ID: <CA+CK2bDswtrqiOMt3+0LBb0+7nJY9aBpzZdsmrWRzy9WxBqKEg@mail.gmail.com>
Date:   Tue, 28 Nov 2023 17:50:01 -0500
From:   Pasha Tatashin <pasha.tatashin@...een.com>
To:     Robin Murphy <robin.murphy@....com>
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Subject: Re: [PATCH 06/16] iommu/dma: use page allocation function provided by iommu-pages.h

On Tue, Nov 28, 2023 at 5:34 PM Robin Murphy <robin.murphy@....com> wrote:
>
> On 2023-11-28 8:49 pm, Pasha Tatashin wrote:
> > Convert iommu/dma-iommu.c to use the new page allocation functions
> > provided in iommu-pages.h.
>
> These have nothing to do with IOMMU pagetables, they are DMA buffers and
> they belong to whoever called the corresponding dma_alloc_* function.

Hi Robin,

This is true, however, we want to account and observe the pages
allocated by IOMMU subsystem for DMA buffers, as they are essentially
unmovable locked pages. Should we separate IOMMU memory from KVM
memory all together and add another field to /proc/meminfo, something
like "iommu -> iommu pagetable and dma memory", or do we want to
export DMA memory separately from IOMMU page tables?

Since, I included DMA memory, I specifically removed mentioning of
IOMMU page tables in the most of places, and only report it as IOMMU
memory. However, since it is still bundled together with SecPageTables
it can be confusing.

Pasha