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

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Date:   Wed, 18 Sep 2019 15:22:42 +0200
From:   Christoph Hellwig <hch@....de>
To:     "Lendacky, Thomas" <Thomas.Lendacky@....com>
Cc:     David Rientjes <rientjes@...gle.com>,
        Christoph Hellwig <hch@....de>,
        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 Tue, Sep 17, 2019 at 06:41:02PM +0000, Lendacky, Thomas wrote:
> > diff --git a/drivers/nvme/host/pci.c b/drivers/nvme/host/pci.c
> > --- a/drivers/nvme/host/pci.c
> > +++ b/drivers/nvme/host/pci.c
> > @@ -1613,7 +1613,8 @@ static int nvme_alloc_admin_tags(struct nvme_dev *dev)
> >  		dev->admin_tagset.timeout = ADMIN_TIMEOUT;
> >  		dev->admin_tagset.numa_node = dev_to_node(dev->dev);
> >  		dev->admin_tagset.cmd_size = sizeof(struct nvme_iod);
> > -		dev->admin_tagset.flags = BLK_MQ_F_NO_SCHED;
> > +		dev->admin_tagset.flags = BLK_MQ_F_NO_SCHED |
> > +					  BLK_MQ_F_BLOCKING;
> 
> I think you want to only set the BLK_MQ_F_BLOCKING if the DMA is required
> to be unencrypted. Unfortunately, force_dma_unencrypted() can't be called
> from a module. Is there a DMA API that could be called to get that info?

The DMA API must support non-blocking calls, and various drivers rely
on that.  So we need to provide that even for the SEV case.  If the
actual blocking can't be made to work we'll need to wire up the DMA
pool in kernel/dma/remap.c for it (and probably move it to separate
file).