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Subject: Re: Regression when booting 5.15 as dom0 on arm64 (WAS: Re:
 [linux-linus test] 161829: regressions - FAIL)
To:     Christoph Hellwig <hch@lst.de>
Cc:     f.fainelli@gmail.com, Stefano Stabellini <sstabellini@kernel.org>,
        "xen-devel@lists.xenproject.org" <xen-devel@lists.xenproject.org>,
        linux-kernel@vger.kernel.org,
        osstest service owner <osstest-admin@xenproject.org>,
        Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>,
        Boris Ostrovsky <boris.ostrovsky@oracle.com>,
        iommu@lists.linux-foundation.org
References: <osstest-161829-mainreport@xen.org>
 <4ea1e89f-a7a0-7664-470c-b3cf773a1031@xen.org> <20210510084057.GA933@lst.de>
From:   Julien Grall <julien@xen.org>
Message-ID: <8b851596-acf7-9d3b-b08a-848cae5adada@xen.org>
Date:   Mon, 10 May 2021 19:15:17 +0100
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Hi Christoph,

On 10/05/2021 09:40, Christoph Hellwig wrote:
> 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);

I have applied the patch on top of 5.13-rc1 and can confirm I am able to 
boot dom0. Are you going to submit the patch?

Thank you for your help!

Best regards,

-- 
Julien Grall