Re: [Xen-devel] Mapping active GDT

[Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>]

On 03/10/2017 09:39 PM, Boris Ostrovsky wrote:
> I am looking into GDT remap series [0] which crashes PV guests and it
> seems that the problem lies in the fact that we cannot establish new
> mapping to an already existing GDT.
>
> The mapping is created by
>
> +static inline void setup_fixmap_gdt(int cpu)
> +{
> +       __set_fixmap(get_cpu_gdt_ro_index(cpu),
> +                    __pa(get_cpu_gdt_rw(cpu)), PAGE_KERNEL);
> +}
>
> with get_cpu_gdt_rw(cpu) being the current GDT pointer. This results in
>
> (XEN) mm.c:2570:d94v0 Bad type (saw 5400000000000001 != exp
> 7000000000000000) for mfn 1538fb (pfn 3e809)
> (XEN) mm.c:1022:d94v0 Could not get page type PGT_writable_page
> (XEN) mm.c:1074:d94v0 Error getting mfn 1538fb (pfn 3e809) from L1 entry
> 80000001538fb063 for l1e_owner=94, pg_owner=94
>
> (after a small change to xen_set_fixmap(), which I think was missing)
>
> Before I try to come up with a fix I wanted to check here to see if this
> (not being able to map active GDT) is indeed the case.

Uhm.. Nevermind. The change in xen_set_fixmap() is probably sufficient.

I was working with wrong branch ;-( Sorry for the noise.

-boris

>
> -boris
>
>
> [0]
> https://lists.xenproject.org/archives/html/xen-devel/2017-03/msg00869.html
>
>
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