Re: [Xen-devel] Backport request

[Daniel Kiper <dkiper@xxxxxxxxxxxx>]

On Mon, Jan 13, 2014 at 11:36:34AM +0000, Jan Beulich wrote:
> >>> On 13.01.14 at 12:30, David Vrabel <david.vrabel@xxxxxxxxxx> wrote:
> > On 13/01/14 11:13, Jan Beulich wrote:
> >>>>> On 13.01.14 at 10:49, Andrew Cooper <andrew.cooper3@xxxxxxxxxx> wrote:
> >>> Can you please backport c/s 0896bd8bea84526b00e00d2d076f4f953a3d73cb
> >>> "x86: map portion of kexec crash area that is within the direct map
> >>> area" to staging-4.3 ASAP, as following the backport of
> >>> 8d611a00d3389d9c16506326e24145b94ac6fb86 "kexec/x86: do not map crash
> >>> kernel area", kexec loading is broken in exactly the same way as it was
> >>> in staging.
> >>
> >> Not without explaining how it is broken: According to my own
> >> checking as well as Daniel's there was no need for the kexec area
> >> to be mapped at all in the old implementation.
> >>
> >> Furthermore, I'd prefer to revert 8d611a00 (dff90d0c on 4.2)
> >> instead if there really is an issue. That's largely because, as
> >> noted in the extra comment I added to 0896bd8b, the change is
> >> still incomplete (and hence not much better than the code with
> >> Daniel's change reverted).
> >
> > In that comment it says:
> >
> >   "That's primarily because map_domain_page()
> >    (needed when the area is outside the direct mapping range) may be
> >    unusable when wanting to kexec due to a crash,"
> >
> > But map_domain_page() is only used when loading the crash image, not
> > during exec.
>
> That's good to know, but I don't think it's a good idea either. Seeing
> that map_domain_page() is being used in the code _at all_ may
> make someone try to use it in a path that is used during kexec. And
> it being used by other functions in the same file may also result in
> one of those functions suddenly also getting used on a kexec path.
>
> Together with the issue of the area potentially ending up in a
> PFN compression hole, to me this is enough reason to still expect
> that these uses get dropped again.

map_domain_page() is used during kexec and crash image load.
However, it is not used when a given image is executed.

Daniel

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