linux-kernel - Re: [PATCH v2] dma-mapping: Use dma_get_mask in dma_addressing

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Message-ID: <20190722145639-mutt-send-email-mst@kernel.org>
Date:   Mon, 22 Jul 2019 14:57:04 -0400
From:   "Michael S. Tsirkin" <mst@...hat.com>
To:     Auger Eric <eric.auger@...hat.com>
Cc:     eric.auger.pro@...il.com, hch@....de, m.szyprowski@...sung.com,
        robin.murphy@....com, jasowang@...hat.com,
        virtualization@...ts.linux-foundation.org,
        iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] dma-mapping: Use dma_get_mask in
 dma_addressing_limited

On Mon, Jul 22, 2019 at 06:56:49PM +0200, Auger Eric wrote:
> Hi Christoph,
> 
> On 7/22/19 6:51 PM, Eric Auger wrote:
> > We currently have cases where the dma_addressing_limited() gets
> > called with dma_mask unset. This causes a NULL pointer dereference.
> > 
> > Use dma_get_mask() accessor to prevent the crash.
> > 
> > Fixes: b866455423e0 ("dma-mapping: add a dma_addressing_limited helper")
> > Signed-off-by: Eric Auger <eric.auger@...hat.com>
> 
> As a follow-up of my last email, here is a patch featuring
> dma_get_mask(). But you don't have the WARN_ON_ONCE anymore, pointing
> out suspect users.

OTOH these users then simply become okay so no need for WARN_ON_ONCE
then :)

> Feel free to pick up your preferred approach
> 
> Thanks
> 
> Eric
> > 
> > ---
> > 
> > v1 -> v2:
> > - was [PATCH 1/2] dma-mapping: Protect dma_addressing_limited
> >   against NULL dma_mask
> > - Use dma_get_mask
> > ---
> >  include/linux/dma-mapping.h | 4 ++--
> >  1 file changed, 2 insertions(+), 2 deletions(-)
> > 
> > diff --git a/include/linux/dma-mapping.h b/include/linux/dma-mapping.h
> > index e11b115dd0e4..f7d1eea32c78 100644
> > --- a/include/linux/dma-mapping.h
> > +++ b/include/linux/dma-mapping.h
> > @@ -689,8 +689,8 @@ static inline int dma_coerce_mask_and_coherent(struct device *dev, u64 mask)
> >   */
> >  static inline bool dma_addressing_limited(struct device *dev)
> >  {
> > -	return min_not_zero(*dev->dma_mask, dev->bus_dma_mask) <
> > -		dma_get_required_mask(dev);
> > +	return min_not_zero(dma_get_mask(dev), dev->bus_dma_mask) <
> > +			    dma_get_required_mask(dev);
> >  }
> >  
> >  #ifdef CONFIG_ARCH_HAS_SETUP_DMA_OPS
> >