Re: Qemu-upstream with Xen

[Roger Pau Monné <roger.pau%entel.upc.edu@localhost>]

On Thu, Jun 14, 2012 at 10:22 AM, Jean-Yves Migeon
<jeanyves.migeon%free.fr@localhost> wrote:
> Le 13/06/2012 18:27, Roger Pau Monné a écrit :
>
>>> Is the P2M table (xpmap_phys_to_machine_mapping) entry for this address
>>> marked as INVALID_MFN?
>>
>>
>> I'm not sure if this is correct, but I've done a:
>>
>> pfn_to_mfn((0x3f800000 - XPMAP_OFFSET) >> PAGE_SHIFT) and it is 239540
>
>
> Should be. Out of interest, what it the value of pfn_to_mfn((0x3f800000) >>
> PAGE_SHIFT
>
> without taking the .text offset into account?

It's the same, 239540.

>> Also, the syscall HYPERVISOR_mmu_update returns the error -22 (EINVAL).
>
>
> It is definitely the hypervisor refusing the mapping, but it does not log
> why (and according to pfn_to_mfn(), this entry is valid, so there is
> something it does not like about it -- maybe a bit set where it is not
> expected to be for this type of address).

My guess is that Xen doesn't like the qemu userspace address we are
passing to it, because in privcmd:433 the mapping of this DomU address
to kernel space succeeds, and the page it's not marked as invalid. But
then the actual mapping, in privpgop_fault fails.

> Next possible step: instrument the hypervisor (xen/arch/x86/mm.c) and see
> the path that leads to EINVAL in do_mmu_update().

Yes, I'm doing this now, will come back with the results, and thanks
for the help :).

Roger.