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

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Message-ID: <20210724001813.07ae518d.pasic@linux.ibm.com>
Date:   Sat, 24 Jul 2021 00:18:13 +0200
From:   Halil Pasic <pasic@...ux.ibm.com>
To:     Christian Borntraeger <borntraeger@...ibm.com>
Cc:     Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
        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>,
        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 19:53:58 +0200
Christian Borntraeger <borntraeger@...ibm.com> wrote:

> On 23.07.21 16:01, Konrad Rzeszutek Wilk wrote:
> > 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@...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...)  
> >>
> >> 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?  
> 
> That would also work for me. I think Halil wanted to send out and v2.

Sorry I didn't interpret your answer correctly. (I interpreted it
like the fixes tags are enough, and those can be added by the maintainer
that is going to merge the patch.) I will send out a v2 right away.

Regards,
Halil