linux-kernel - Re: [bug] __blk_mq_run_hw_queue suspicious rcu usage

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Message-ID: <20191128064056.GA19822@lst.de>
Date:   Thu, 28 Nov 2019 07:40:56 +0100
From:   Christoph Hellwig <hch@....de>
To:     David Rientjes <rientjes@...gle.com>
Cc:     Christoph Hellwig <hch@....de>,
        "Lendacky, Thomas" <Thomas.Lendacky@....com>,
        Keith Busch <kbusch@...nel.org>, Jens Axboe <axboe@...nel.dk>,
        "Singh, Brijesh" <brijesh.singh@....com>,
        Ming Lei <ming.lei@...hat.com>,
        Peter Gonda <pgonda@...gle.com>,
        Jianxiong Gao <jxgao@...gle.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "x86@...nel.org" <x86@...nel.org>,
        "iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>
Subject: Re: [bug] __blk_mq_run_hw_queue suspicious rcu usage

On Wed, Nov 27, 2019 at 02:11:28PM -0800, David Rientjes wrote:
> So we're left with making dma_pool_alloc(GFP_ATOMIC) actually be atomic 
> even when the DMA needs to be unencrypted for SEV.  Christoph's suggestion 
> was to wire up dmapool in kernel/dma/remap.c for this.  Is that necessary 
> to be done for all devices that need to do dma_pool_alloc(GFP_ATOMIC) or 
> can we do it within the DMA API itself so it's transparent to the driver?

It needs to be transparent to the driver.  Lots of drivers use GFP_ATOMIC
dma allocations, and all of them are broken on SEV setups currently.