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

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Message-ID: <62da6479-a000-0b1a-d251-c4e27616fbc2@de.ibm.com>
Date:   Fri, 23 Jul 2021 07:51:24 +0200
From:   Christian Borntraeger <borntraeger@...ibm.com>
To:     Halil Pasic <pasic@...ux.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>,
        Heiko Carstens <heiko.carstens@...ibm.com>,
        Vasily Gorbik <gor@...ux.ibm.com>
Subject: Re: [PATCH v2 0/4] Fix restricted DMA vs swiotlb_exit()



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.

> 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>

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)
>