Re: [PATCH v2 0/4] Fix restricted DMA vs swiotlb_exit()

[Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>]

On Fri, Jul 23, 2021 at 10:50:57AM +0200, Christian Borntraeger wrote:
> 
> 
> On 23.07.21 10:47, Halil Pasic wrote:
> > On Fri, 23 Jul 2021 08:14:19 +0200
> > Christian Borntraeger <borntraeger@de.ibm.com> wrote:
> > 
> > > Resending with the correct email of Heiko....
> > > 
> > > On 23.07.21 03:12, Halil Pasic wrote:
> > > > On Thu, 22 Jul 2021 21:22:58 +0200
> > > > Christian Borntraeger <borntraeger@de.ibm.com> wrote:
> > > > > On 20.07.21 15:38, Will Deacon wrote:
> > > > > > Hi again, folks,
> > > > > > 
> > > > > > This is version two of the patch series I posted yesterday:
> > > > > > 
> > > > > >      https://lore.kernel.org/r/20210719123054.6844-1-will@kernel.org
> > > > > > 
> > > > > > The only changes since v1 are:
> > > > > > 
> > > > > >      * Squash patches 2 and 3, amending the commit message accordingly
> > > > > >      * Add Reviewed-by and Tested-by tags from Christoph and Claire (thanks!)
> > > > > > 
> > > > > > I'd usually leave it a bit longer between postings, but since this fixes
> > > > > > issues with patches in -next I thought I'd spin a new version immediately.
> > > > > > 
> > > > > > Cheers,
> > > > > 
> > > > > FWIW, I just bisected virtio-errors with secure execution mode
> > > > > qemu-system-s390x: virtio-serial-bus: Unexpected port id 4205794771 for device virtio-serial0.0
> > > > > 
> > > > > to
> > > > > commit 903cd0f315fe426c6a64c54ed389de0becb663dc
> > > > > Author: Claire Chang <tientzu@chromium.org>
> > > > > Date:   Thu Jun 24 23:55:20 2021 +0800
> > > > > 
> > > > >         swiotlb: Use is_swiotlb_force_bounce for swiotlb data bouncing
> > > > > 
> > > > > Unfortunately this patch series does NOT fix this issue, so it seems that even more
> > > > > things are broken.
> > > > > 
> > > > > Any idea what else might be broken?
> > > > 
> > > > I've done some debugging, and I think I know what is going on. Since
> > > > that commit we need to set force_swiotlb before the swiotlb itself is
> > > > initialized. So the patch below should fix the problem.
> > > > 
> > > > --------------------8<-------------------------------------
> > > > 
> > > > From: Halil Pasic <pasic@linux.ibm.com>
> > > > Date: Fri, 23 Jul 2021 02:57:06 +0200
> > > > Subject: [PATCH 1/1] s390/pv: fix the forcing of the swiotlb
> > > > 
> > > > Since commit 903cd0f315fe ("swiotlb: Use is_swiotlb_force_bounce for
> > > > swiotlb data bouncing") if code sets swiotlb_force it needs to do so
> > > > before the swiotlb is initialised. Otherwise
> > > > io_tlb_default_mem->force_bounce will not get set to true, and devices
> > > > that use (the default) swiotlb will not bounce  despite switolb_force
> > > > having the value of SWIOTLB_FORCE.
> > > > 
> > > > Let us restore swiotlb functionality for PV by fulfilling this new
> > > > requirement.
> > > I would add:
> > > Fixes: 903cd0f315fe ("swiotlb: Use is_swiotlb_force_bounce for swiotlb data bouncing")
> > > as this patch breaks things
> > > and
> > > Fixes: 64e1f0c531d1 ("s390/mm: force swiotlb for protected virtualization")
> > > 
> > > to make the s390 init code more robust in case people start backporting things.
> > 
> > I agree. Do we want this backported to the stable releases that have
> > 64e1f0c531d1  (i.e. do we need a cc stable) or should the fixes tag just
> > serve as metadata? My guess is, it's the former. In that sense should I
> > add the tags along with an explanation for the second fixes respin with
> > cc stable?
> > 
> > (BTW I don't think this formally qualifies for the stable backports, but
> > I hope we can make an exception...)
> 
> I think it makes sense for stable as it is cleaner to set the flags before
> calling the init function. cc stable would be better and the right way
> according to process, but the Fixes tag is mostly enough.

But the reaso for fixing this is for code that is not yet in Linus's
tree?

I can just pick this patch up and add it in the pile I have for the next
merge window?
> 
> > 
> > > 
> > > > Signed-off-by: Halil Pasic <pasic@linux.ibm.com>
> > > 
> > > I can confirm that this fixes the problem. This also makes sense codewise.
> > > 
> > > Tested-by: Christian Borntraeger <borntraeger@de.ibm.com>
> > > Reviewed-by: Christian Borntraeger <borntraeger@de.ibm.com>
> > 
> > Thanks!
> > 
> > Regards,
> > Halil
> > > 
> > > Konrad, Heiko, Vasily, any preference which tree this goes? I think s390
> > > would be easiest, but that requires that the patches in the swiotlb tree have
> > > fixed commit IDs.
> > > 
> > > > ---
> > > >    arch/s390/mm/init.c | 2 +-
> > > >    1 file changed, 1 insertion(+), 1 deletion(-)
> > > > 
> > > > diff --git a/arch/s390/mm/init.c b/arch/s390/mm/init.c
> > > > index 8ac710de1ab1..07bbee9b7320 100644
> > > > --- a/arch/s390/mm/init.c
> > > > +++ b/arch/s390/mm/init.c
> > > > @@ -186,9 +186,9 @@ static void pv_init(void)
> > > >    		return;
> > > >    	/* make sure bounce buffers are shared */
> > > > +	swiotlb_force = SWIOTLB_FORCE;
> > > >    	swiotlb_init(1);
> > > >    	swiotlb_update_mem_attributes();
> > > > -	swiotlb_force = SWIOTLB_FORCE;
> > > >    }
> > > >    void __init mem_init(void)
> > 
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