From mboxrd@z Thu Jan  1 00:00:00 1970
From: Don Slutz <dslutz@verizon.com>
Subject: Re: [PATCHv2] x86: map portion of kexec crash area that
 is within the direct map area
Date: Wed, 08 Jan 2014 15:54:26 -0500
Message-ID: <52CDBB02.6070702@terremark.com>
References: <1389206119-13527-1-git-send-email-david.vrabel@citrix.com>
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To: David Vrabel <david.vrabel@citrix.com>, xen-devel@lists.xen.org
Cc: Daniel Kiper <daniel.kiper@oracle.com>, Don Slutz <dslutz@verizon.com>, Jan Beulich <jbeulich@suse.com>
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On 01/08/14 13:35, David Vrabel wrote:
> From: David Vrabel <david.vrabel@citrix.com>
>
> Commit 7113a45451a9f656deeff070e47672043ed83664 (kexec/x86: do not map
> crash kernel area) causes fatal page faults when loading a crash
> image.  The attempt to zero the first control page allocated from the
> crash region will fault as the VA return by map_domain_page() has no
> mapping.
>
> The fault will occur on non-debug builds of Xen when the crash area is
> below 5 TiB (which will be most systems).
>
> The assumption that the crash area mapping was not used is incorrect.
> map_domain_page() is used when loading an image and building the
> image's page tables to temporarily map the crash area, thus the
> mapping is required if the crash area is in the direct map area.
>
> Reintroduce the mapping, but only the portions of the crash area that
> are within the direct map area.
>
> Reported-by: Don Slutz <dslutz@verizon.com>
> Signed-off-by: David Vrabel <david.vrabel@citrix.com>
> Cc: Daniel Kiper <daniel.kiper@oracle.com>
> ---
> This fixes a Xen crash so is an important fix for the 4.4 release..
>
> Changes in v2:
> - merge patches into one
> - add check for e > s before mapping
> ---
>   xen/arch/x86/setup.c |   11 +++++++++++
>   1 files changed, 11 insertions(+), 0 deletions(-)
>
> diff --git a/xen/arch/x86/setup.c b/xen/arch/x86/setup.c
> index 4833ca3..b49256d 100644
> --- a/xen/arch/x86/setup.c
> +++ b/xen/arch/x86/setup.c
> @@ -1098,6 +1098,17 @@ void __init __start_xen(unsigned long mbi_p)
>                            PFN_UP(mod[i].mod_end), PAGE_HYPERVISOR);
>       }
>   
> +    if ( kexec_crash_area.size )
> +    {
> +        unsigned long s = PFN_DOWN(kexec_crash_area.start);
> +        unsigned long e = min(s + PFN_UP(kexec_crash_area.size),
> +                              PFN_UP(__pa(HYPERVISOR_VIRT_END - 1)));
> +
> +        if ( e > s )
> +            map_pages_to_xen((unsigned long)__va(kexec_crash_area.start),
> +                             s, e - s, PAGE_HYPERVISOR);
> +    }
> +
>       xen_virt_end = ((unsigned long)_end + (1UL << L2_PAGETABLE_SHIFT) - 1) &
>                      ~((1UL << L2_PAGETABLE_SHIFT) - 1);
>       destroy_xen_mappings(xen_virt_end, XEN_VIRT_START + BOOTSTRAP_MAP_BASE);


4.4.0-rc1 + this patch works for me.  So you can add:

Tested-by: Don Slutz <dslutz@verizon.com>

    -Don Slutz