linux-kernel - Re: [PATCH RFC 0/2] dma-pool: allow user to disable atomic pool

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Message-ID: <YRNluS1qt1YL2r7p@infradead.org>
Date:   Wed, 11 Aug 2021 06:52:57 +0100
From:   Christoph Hellwig <hch@...radead.org>
To:     Tom Lendacky <thomas.lendacky@....com>
Cc:     Baoquan He <bhe@...hat.com>, Robin Murphy <robin.murphy@....com>,
        Christoph Hellwig <hch@...radead.org>, brijesh.singh@....com,
        x86@...nel.org, kexec@...ts.infradead.org,
        linux-kernel@...r.kernel.org, rppt@...ux.ibm.com,
        linux-mm@...ck.org, iommu@...ts.linux-foundation.org,
        rientjes@...gle.com
Subject: Re: [PATCH RFC 0/2] dma-pool: allow user to disable atomic pool

On Tue, Aug 10, 2021 at 03:52:25PM -0500, Tom Lendacky via iommu wrote:
> I think the atomic pool is used by the NVMe driver. My understanding is
> that driver will do a dma_alloc_coherent() from interrupt context, so it
> needs to use GFP_ATOMIC. The pool was created because dma_alloc_coherent()
> would perform a set_memory_decrypted() call, which can sleep. The pool
> eliminates that issue (David can correct me if I got that wrong).

Not just the NVMe driver.  We have plenty of drivers doing that, just
do a quick grep for dma_alloc_* dma_poll_alloc, dma_pool_zalloc with
GFP_ATOMIC (and that won't even find multi-line strings).