Re: Regression when booting 5.15 as dom0 on arm64 (WAS: Re: [linux-linus test] 161829: regressions - FAIL)

[Christoph Hellwig <hch@xxxxxx>]

On Sat, May 08, 2021 at 12:32:37AM +0100, Julien Grall wrote:
> The pointer dereferenced seems to suggest that the swiotlb hasn't been 
> allocated. From what I can tell, this may be because swiotlb_force is set 
> to SWIOTLB_NO_FORCE, we will still enable the swiotlb when running on top 
> of Xen.
>
> I am not entirely sure what would be the correct fix. Any opinions?

Can you try something like the patch below (not even compile tested, but
the intent should be obvious?


diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c
index 16a2b2b1c54d..7671bc153fb1 100644
--- a/arch/arm64/mm/init.c
+++ b/arch/arm64/mm/init.c
@@ -44,6 +44,8 @@
 #include <asm/tlb.h>
 #include <asm/alternative.h>
 
+#include <xen/arm/swiotlb-xen.h>
+
 /*
  * We need to be able to catch inadvertent references to memstart_addr
  * that occur (potentially in generic code) before arm64_memblock_init()
@@ -482,7 +484,7 @@ void __init mem_init(void)
        if (swiotlb_force == SWIOTLB_FORCE ||
            max_pfn > PFN_DOWN(arm64_dma_phys_limit))
                swiotlb_init(1);
-       else
+       else if (!IS_ENABLED(CONFIG_XEN) || !xen_swiotlb_detect())
                swiotlb_force = SWIOTLB_NO_FORCE;
 
        set_max_mapnr(max_pfn - PHYS_PFN_OFFSET);