Re: [Xen-devel] Current staging crashes on boot on an AMD EPYC 7251

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 21.09.18 at 13:05, <roger.pau@xxxxxxxxxx> wrote:
> On Fri, Sep 21, 2018 at 05:00:54AM -0600, Jan Beulich wrote:
>> >>> On 21.09.18 at 12:48, <rcojocaru@xxxxxxxxxxxxxxx> wrote:
>> > On 9/21/18 1:41 PM, Jan Beulich wrote:
>> >>>>> On 21.09.18 at 12:15, <roger.pau@xxxxxxxxxx> wrote:
>> >>> On Fri, Sep 21, 2018 at 12:45:18PM +0300, Razvan Cojocaru wrote:
>> >>>> While doing my best to make sure what I understand to be George's
>> >>>> proposed changes for the altp2m series I've tried to boot Xen staging on
>> >>>> an AMD host, but it crashes in an unrelated place (I've tested this by
>> >>>> stashing my changes and booting a "vanilla" staging):
>> >>>
>> >>> Can you apply the following debug patch and paste the full boot log?
>> >> 
>> >> Well, not having provided the full boot log right away is clearly
>> >> unhelpful, as from that alone we should be able to tell what's
>> >> going on here (unless we e.g. screw up the E820 map somewhere).
>> >> However, it is already clear that ...
>> >> 
>> >>> --- a/xen/arch/x86/mm.c
>> >>> +++ b/xen/arch/x86/mm.c
>> >>> @@ -465,6 +465,8 @@ unsigned int page_get_ram_type(mfn_t mfn)
>> >>>              break;
>> >>>  
>> >>>          default:
>> >>> +printk("[%#lx, %#lx) type: %u\n", e820.map[i].addr,
>> >>> +       e820.map[i].addr + e820.map[i].size, e820.map[i].type);
>> >>>              ASSERT_UNREACHABLE();
>> >> 
>> >> ... this assertion needs to go away, as it would trigger for both
>> >> E820_TYPE_PMEM and E820_TYPE_PRAM (using the Linux
>> >> naming), or the unnamed type 6 mentioned in their header. It
>> >> would also trigger for types which may get added down the road.
>> > 
>> > I have attached the full log, as requested by Roger.
>> 
>> And there we go:
>> 
>> (XEN)  00000000dabf2000 - 00000000dacdf000 type 20
>> 
>> Whatever that is. I think for the purposes of the function here all
>> unknown types should be mapped into UNUSABLE.
> 
> Oh, I sent a patch to map them to RAM_TYPE_UNKNOWN, but maybe UNUSABLE
> would be better?
> 
> For the current usage of page_get_ram_type both will accomplish the
> same.

Which one is better ultimately depends on the callers, and as you
say for the only current one it doesn't matter. Therefore I guess I'm
fine either way.

Jan



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