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From: Christoph Hellwig <hch@lst.de>
To: David Rientjes <rientjes@google.com>
Cc: Tom Lendacky <thomas.lendacky@amd.com>,
	Brijesh Singh <brijesh.singh@amd.com>,
	Christoph Hellwig <hch@lst.de>, Jens Axboe <axboe@kernel.dk>,
	Ming Lei <ming.lei@redhat.com>, Peter Gonda <pgonda@google.com>,
	Jianxiong Gao <jxgao@google.com>,
	linux-kernel@vger.kernel.org, x86@kernel.org,
	iommu@lists.linux-foundation.org
Subject: Re: [bug] __blk_mq_run_hw_queue suspicious rcu usage
Date: Thu, 5 Sep 2019 08:06:27 +0200	[thread overview]
Message-ID: <20190905060627.GA1753@lst.de> (raw)
In-Reply-To: <alpine.DEB.2.21.1909041434580.160038@chino.kir.corp.google.com>

On Wed, Sep 04, 2019 at 02:40:44PM -0700, David Rientjes wrote:
> Hi Christoph, Jens, and Ming,
> 
> While booting a 5.2 SEV-enabled guest we have encountered the following 
> WARNING that is followed up by a BUG because we are in atomic context 
> while trying to call set_memory_decrypted:

Well, this really is a x86 / DMA API issue unfortunately.  Drivers
are allowed to do GFP_ATOMIC dma allocation under locks / rcu critical
sections and from interrupts.  And it seems like the SEV case can't
handle that.  We have some semi-generic code to have a fixed sized
pool in kernel/dma for non-coherent platforms that have similar issues
that we could try to wire up, but I wonder if there is a better way
to handle the issue, so I've added Tom and the x86 maintainers.

Now independent of that issue using DMA coherent memory for the nvme
PRPs/SGLs doesn't actually feel very optional.  We could do with
normal kmalloc allocations and just sync it to the device and back.
I wonder if we should create some general mempool-like helpers for that.

  reply	other threads:[~2019-09-05  6:06 UTC|newest]

Thread overview: 13+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-09-04 21:40 [bug] __blk_mq_run_hw_queue suspicious rcu usage David Rientjes
2019-09-05  6:06 ` Christoph Hellwig [this message]
2019-09-05 22:37   ` David Rientjes
2019-09-16 23:45     ` David Rientjes
2019-09-17 18:23       ` David Rientjes
2019-09-17 18:32         ` Jens Axboe
2019-09-17 18:41         ` Lendacky, Thomas
2019-09-18 13:22           ` Christoph Hellwig
2019-11-27 22:11             ` David Rientjes
2019-11-28  6:40               ` Christoph Hellwig
2019-12-13  0:07                 ` David Rientjes
2019-12-13  9:33                   ` David Rientjes
2019-12-15  5:38                   ` David Rientjes

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