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

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Date:   Fri, 23 Jul 2021 03:12:52 +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>,
        Halil Pasic <pasic@...ux.ibm.com>
Subject: Re: [PATCH v2 0/4] Fix restricted DMA vs swiotlb_exit()

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.

Signed-off-by: Halil Pasic <pasic@...ux.ibm.com>
---
 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)
-- 
2.29.2