linux-kernel - Re: [PATCH v2 1/1] s390/pv: fix the forcing of the swiotlb

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Date:   Fri, 23 Jul 2021 20:27:56 -0400
From:   Konrad Rzeszutek Wilk <konrad@...nok.org>
To:     Halil Pasic <pasic@...ux.ibm.com>
Cc:     Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
        iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org,
        Christian Borntraeger <borntraeger@...ibm.com>,
        Nathan Chancellor <nathan@...nel.org>,
        Vasily Gorbik <gor@...ux.ibm.com>,
        linux-s390 <linux-s390@...r.kernel.org>,
        Robin Murphy <robin.murphy@....com>,
        Heiko Carstens <hca@...ux.ibm.com>, stable@...r.kernel.org,
        Claire Chang <tientzu@...omium.org>,
        Will Deacon <will@...nel.org>, Christoph Hellwig <hch@....de>,
        Guenter Roeck <linux@...ck-us.net>
Subject: Re: [PATCH v2 1/1] s390/pv: fix the forcing of the swiotlb

On Sat, Jul 24, 2021 at 01:17:46AM +0200, Halil Pasic wrote:
> 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.
> 
> This change addresses what turned out to be a fragility in
> commit 64e1f0c531d1 ("s390/mm: force swiotlb for protected
> virtualization"), which ain't exactly broken in its original context,
> but could give us some more headache if people backport the broken
> change and forget this fix.
> 
> Signed-off-by: Halil Pasic <pasic@...ux.ibm.com>
> Tested-by: Christian Borntraeger <borntraeger@...ibm.com>
> Reviewed-by: Christian Borntraeger <borntraeger@...ibm.com>
> Fixes: 903cd0f315fe ("swiotlb: Use is_swiotlb_force_bounce for swiotlb data bouncing")
> Fixes: 64e1f0c531d1 ("s390/mm: force swiotlb for protected virtualization")
> Cc: stable@...r.kernel.org #5.3+
> 
> ---

Picked it up and stuck it in linux-next with the other set of patches (Will's fixes).