From: David Rientjes via iommu <iommu@lists.linux-foundation.org>
To: Christoph Hellwig <hch@lst.de>
Cc: Jens Axboe <axboe@kernel.dk>,
Tom Lendacky <thomas.lendacky@amd.com>,
Brijesh Singh <brijesh.singh@amd.com>,
x86@kernel.org, linux-kernel@vger.kernel.org,
Ming Lei <ming.lei@redhat.com>,
iommu@lists.linux-foundation.org, Peter Gonda <pgonda@google.com>,
Jianxiong Gao <jxgao@google.com>
Subject: Re: [bug] __blk_mq_run_hw_queue suspicious rcu usage
Date: Thu, 5 Sep 2019 15:37:16 -0700 (PDT) [thread overview]
Message-ID: <alpine.DEB.2.21.1909051534050.245316@chino.kir.corp.google.com> (raw)
In-Reply-To: <20190905060627.GA1753@lst.de>
On Thu, 5 Sep 2019, Christoph Hellwig 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.
>
Thanks for looking into this. I assume it's a non-starter to try to
address this in _vm_unmap_aliases() itself, i.e. rely on a purge spinlock
to do all synchronization (or trylock if not forced) for
purge_vmap_area_lazy() rather than only the vmap_area_lock within it. In
other words, no mutex.
If that's the case, and set_memory_encrypted() can't be fixed to not need
to sleep by changing _vm_unmap_aliases() locking, then I assume dmapool is
our only alternative? I have no idea with how large this should be.
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next prev parent reply other threads:[~2019-09-05 22:37 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <alpine.DEB.2.21.1909041434580.160038@chino.kir.corp.google.com>
2019-09-05 6:06 ` [bug] __blk_mq_run_hw_queue suspicious rcu usage Christoph Hellwig
2019-09-05 22:37 ` David Rientjes via iommu [this message]
2019-09-16 23:45 ` David Rientjes via iommu
2019-09-17 18:23 ` David Rientjes via iommu
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 via iommu
2019-11-28 6:40 ` Christoph Hellwig
2019-12-13 0:07 ` David Rientjes via iommu
2019-12-13 9:33 ` David Rientjes via iommu
2019-12-15 5:38 ` David Rientjes via iommu
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