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

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Message-Id: <20210723231746.3964989-1-pasic@linux.ibm.com>
Date:   Sat, 24 Jul 2021 01:17:46 +0200
From:   Halil Pasic <pasic@...ux.ibm.com>
To:     Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
        iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org,
        Christian Borntraeger <borntraeger@...ibm.com>
Cc:     Halil Pasic <pasic@...ux.ibm.com>, stable@...r.kernel.org,
        Guenter Roeck <linux@...ck-us.net>,
        Will Deacon <will@...nel.org>,
        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: [PATCH v2 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.

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+

---

I'm aware that this fix does not really satisfy the formal requirements
for the stable process. But to avoid problems with backports we would
like this fix applied to 5.3+ stable kernels.
---
 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 d85bd7f5d8dc..1c8f8ccebfb7 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)

base-commit: 90d856e71443a2fcacca8e7539bac44d9cb3f7ab
-- 
2.25.1