RE: [Xen-devel] dom0 boot failure with 256G

["Ian Pratt" <Ian.Pratt@xxxxxxxxxxxxx>]

>     I've been intensely debugging a dom0 crash right at boot in
>     pagetable_init() with 256G. We are running 64bit hyp with 32bit
> dom0.
>     This on xen 3.1.3, which seems to have fixes from changeset 16548.

256GB is more than a 32b dom0 can handle. Presumably it works if you set
dom0_mem= to something smaller?

We should probably make the clipping of dom0 memory to something like
64GB automatic.

Ian

 
>     It boils down to this:
> 
>    crash occurs in dom0: mfn_to_pfn() during
> machine_to_phys_mapping[mfn]
>    lookup  where mfn == 0x3f2ec09 is too big. The table starts at:
> 0xf5800000
>    which I see comes from MACH2PHYS_VIRT_START.
> 
>    Trying to figure the hyp out, I notice phys addr is set as:
> 
>    d->arch.physaddr_bitsize =
>            fls((1UL << 32) - HYPERVISOR_COMPAT_VIRT_START(d)) - 1
>              + (PAGE_SIZE - 2);
>    which is set to 0x1019, totally baffling me. I'd expect it to be
32,
>    36, or 64????????
> 
>   moving along, in alloc_domheap_pages() :
>     bits = domain_clamp_alloc_bitsize(d, bits ? :
> (BITS_PER_LONG+PAGE_SHIFT));
> 
>    domain_clamp_alloc_bitsize(struct domain *d, unsigned int bits)
>    {
>        if ( (d == NULL) || !is_pv_32on64_domain(d) )
>                return bits;
>        return min(d->arch.physaddr_bitsize, bits);
>             ---> here : physaddr: 0x1019, bits:76 ?????
>             ---> i'm thinking bits should be 36+12 == 48 ??
>    }
> 
>     finally, call to alloc_heap_pages(...) returns frames too high, pg
>     ptr is returned at : ffff82849df30000 (zone_hi == 0x27)
> 
> 
>     On a side note, is my understanding correct that while a guest pfn
> must
>     always be < 36 bits for a PAE 32 guest, the mfn doesn't have to
be?
> 
> 
>     thanks
>     mukesh
> 
> 
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