linux-kernel - Re: [PATCH v2 0/4] Fix restricted DMA vs swiotlb

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Message-ID: <20210723104701.3f8ac227.pasic@linux.ibm.com>
Date:   Fri, 23 Jul 2021 10:47:01 +0200
From:   Halil Pasic <pasic@...ux.ibm.com>
To:     Christian Borntraeger <borntraeger@...ibm.com>
Cc:     Will Deacon <will@...nel.org>, iommu@...ts.linux-foundation.org,
        linux-kernel@...r.kernel.org, Guenter Roeck <linux@...ck-us.net>,
        Claire Chang <tientzu@...omium.org>,
        Christoph Hellwig <hch@....de>,
        Robin Murphy <robin.murphy@....com>,
        Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
        Nathan Chancellor <nathan@...nel.org>,
        linux-s390 <linux-s390@...r.kernel.org>,
        Vasily Gorbik <gor@...ux.ibm.com>,
        Heiko Carstens <hca@...ux.ibm.com>
Subject: Re: [PATCH v2 0/4] Fix restricted DMA vs swiotlb_exit()

On Fri, 23 Jul 2021 08:14:19 +0200
Christian Borntraeger <borntraeger@...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@...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@...omium.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@...ux.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...)

> 
> > Signed-off-by: Halil Pasic <pasic@...ux.ibm.com>  
> 
> I can confirm that this fixes the problem. This also makes sense codewise.
> 
> Tested-by: Christian Borntraeger <borntraeger@...ibm.com>
> Reviewed-by: Christian Borntraeger <borntraeger@...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)
> >