From: Christoph Hellwig <hch@lst.de>

Although SWIOTLB_NO_FORCE is meant to allow later calls to swiotlb_init,
today dma_direct_map_page returns error if SWIOTLB_NO_FORCE.

For now, without a larger overhaul of SWIOTLB_NO_FORCE, the best we can
do is to avoid setting SWIOTLB_NO_FORCE in mem_init when we know that it
is going to be required later (e.g. Xen requires it).

CC: boris.ostrovsky@oracle.com
CC: jgross@suse.com
CC: catalin.marinas@arm.com
CC: will@kernel.org
CC: linux-arm-kernel@lists.infradead.org
Fixes: 2726bf3ff252 ("swiotlb: Make SWIOTLB_NO_FORCE perform no allocation")
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Stefano Stabellini <stefano.stabellini@xilinx.com>

---
Changes in v2:
- patch split
---
 arch/arm64/mm/init.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c
index 16a2b2b1c54d..e55409caaee3 100644
--- a/arch/arm64/mm/init.c
+++ b/arch/arm64/mm/init.c
@@ -43,6 +43,7 @@
 #include <linux/sizes.h>
 #include <asm/tlb.h>
 #include <asm/alternative.h>
+#include <asm/xen/swiotlb-xen.h>
 
 /*
  * We need to be able to catch inadvertent references to memstart_addr
@@ -482,7 +483,7 @@ void __init mem_init(void)
 	if (swiotlb_force == SWIOTLB_FORCE ||
 	    max_pfn > PFN_DOWN(arm64_dma_phys_limit))
 		swiotlb_init(1);
-	else
+	else if (!xen_swiotlb_detect())
 		swiotlb_force = SWIOTLB_NO_FORCE;
 
 	set_max_mapnr(max_pfn - PHYS_PFN_OFFSET);
-- 
2.17.1

On 12.05.21 22:18, Stefano Stabellini wrote:
> From: Christoph Hellwig <hch@lst.de>
> 
> Although SWIOTLB_NO_FORCE is meant to allow later calls to swiotlb_init,
> today dma_direct_map_page returns error if SWIOTLB_NO_FORCE.
> 
> For now, without a larger overhaul of SWIOTLB_NO_FORCE, the best we can
> do is to avoid setting SWIOTLB_NO_FORCE in mem_init when we know that it
> is going to be required later (e.g. Xen requires it).
> 
> CC: boris.ostrovsky@oracle.com
> CC: jgross@suse.com
> CC: catalin.marinas@arm.com
> CC: will@kernel.org
> CC: linux-arm-kernel@lists.infradead.org
> Fixes: 2726bf3ff252 ("swiotlb: Make SWIOTLB_NO_FORCE perform no allocation")
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> Signed-off-by: Stefano Stabellini <stefano.stabellini@xilinx.com>

Reviewed-by: Juergen Gross <jgross@suse.com>


Juergen

On Wed, May 12, 2021 at 01:18:22PM -0700, Stefano Stabellini wrote:
> From: Christoph Hellwig <hch@lst.de>
> 
> Although SWIOTLB_NO_FORCE is meant to allow later calls to swiotlb_init,
> today dma_direct_map_page returns error if SWIOTLB_NO_FORCE.
> 
> For now, without a larger overhaul of SWIOTLB_NO_FORCE, the best we can
> do is to avoid setting SWIOTLB_NO_FORCE in mem_init when we know that it
> is going to be required later (e.g. Xen requires it).
> 
> CC: boris.ostrovsky@oracle.com
> CC: jgross@suse.com
> CC: catalin.marinas@arm.com
> CC: will@kernel.org
> CC: linux-arm-kernel@lists.infradead.org
> Fixes: 2726bf3ff252 ("swiotlb: Make SWIOTLB_NO_FORCE perform no allocation")
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> Signed-off-by: Stefano Stabellini <stefano.stabellini@xilinx.com>

Acked-by: Catalin Marinas <catalin.marinas@arm.com>