Re: [Xen-devel] [BUGFIX] [PATCH] kexec/x86: Do map crash kernel area

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 02.01.14 at 11:46, David Vrabel <david.vrabel@xxxxxxxxxx> wrote:
> On 01/01/14 16:51, Don Slutz wrote:
>> Revert of commit 7113a45451a9f656deeff070e47672043ed83664
> 
> Since this commit introduced a regression, a revert is the best thing to
> do here.
> 
> Acked-by: David Vrabel <david.vrabel@xxxxxxxxxx>

I don't agree: Reverting this would imply restoring the issue with
mapping the kexec range even when outside the direct map area.

Furthermore I intend to backport this change, as from all I can
tell prior to your rework of the kexec code it was entirely unused
(and hence should never have been there).

>> +    map_pages_to_xen((unsigned long)__va(kexec_crash_area.start),
>> +                     kexec_crash_area.start >> PAGE_SHIFT,
>> +                     PFN_UP(kexec_crash_area.size), PAGE_HYPERVISOR);
>> +
> 
> This should be made conditional on the location of the crash region --
> it is wrong to do this for portions of the crash region that are outside
> the crash region.

Either that or the kexec code would become independent of the
specific behavioral aspects of the direct map and map_domain_page().
It's the latter that I'd prefer, not the least because I'm getting the
impression that restoring the code (even if conditional) would still not
help when the kexec area is not only outside the direct map area, but
beyond accessible RAM boundaries (i.e. on MFNs for which mfn_valid()
would return false).

Jan


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