[Xen-devel] Re: trip to shanghai

[Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>]

CC'ing Tim and xen-devel

On Mon, 18 Jul 2011, Jiageng Yu wrote:
> 2011/7/16 Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>:
> > On Fri, 15 Jul 2011, Jiageng Yu wrote:
> >> 2011/7/15 Jiageng Yu <yujiageng734@xxxxxxxxx>:
> >> > 2011/7/15 Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>:
> >> >> On Fri, 15 Jul 2011, Jiageng Yu wrote:
> >> >>> > Does it mean you are actually able to boot an HVM guest using Linux
> >> >>> > based stubdoms?? Did you manage to solve the framebuffer problem too?
> >> >>>
> >> >>>
> >> >>> The HVM guest is booted. But the boot process is terminated because
> >> >>> vga bios is not invoked by seabios. I have got stuck here for a week.
> >> >>>
> >> >>
> >> >> There was a bug in xen-unstable.hg or seabios that would prevent vga 
> >> >> bios from
> >> >> being loaded, it should be fixed now.
> >> >>
> >> >> Alternatively you can temporarely work around the issue with this hacky 
> >> >> patch:
> >> >>
> >> >> ---
> >> >>
> >> >>
> >> >> diff -r 00d2c5ca26fd tools/firmware/hvmloader/hvmloader.c
> >> >> --- a/tools/firmware/hvmloader/hvmloader.c   ÂFri Jul 08 18:35:24 
> >> >> 2011 +0100
> >> >> +++ b/tools/firmware/hvmloader/hvmloader.c   ÂFri Jul 15 11:37:12 
> >> >> 2011 +0000
> >> >> @@ -430,7 +430,7 @@ int main(void)
> >> >> Â Â Â Â Â Â bios->create_pir_tables();
> >> >> Â Â }
> >> >>
> >> >> - Â Âif ( bios->load_roms )
> >> >> + Â Âif ( 1 )
> >> >> Â Â {
> >> >> Â Â Â Â switch ( virtual_vga )
> >> >> Â Â Â Â {
> >> >>
> >> >>
> >> >
> >> > Yes. Vga bios is booted. However, the upstram qemu receives a SIGSEGV
> >> > signal subsequently. I am trying to print the call stack when
> >> > receiving the signal.
> >> >
> >>
> >> Hi,
> >>
> >> Â ÂI find the cause of SIGSEGV signal:
> >>
> >> Â Âcpu_physical_memory_rw(target_phys_addr_t addr, uint8_t *buf, int
> >> len, int is_write)
> >> Â Â Â Â Â Â Â Â Â ->memcpy(buf, ptr + (addr & ~TARGET_PAGE_MASK), l);
> >>
> >> Â Â In my case, ptr=0 and addr=0xc253e, when qemu attempts to vist
> >> 0x53e address, the SIGSEGV signal is generated.
> >>
> >> Â Â I believe the qemu is trying to vist vram in this moment. This
> >> code seems no problem, and I will continue to find the root cause.
> >>
> >
> > The vram is allocated by qemu, see hw/vga.c:vga_common_init.
> > qemu_ram_alloc under xen ends up calling xen_ram_alloc that calls
> > xc_domain_populate_physmap_exact.
> > xc_domain_populate_physmap_exact is the hypercall that should ask Xen to
> > add the missing vram pages in the guest. Maybe this hypercall is failing
> > in your case?
> 
> 
> Hi,
> 
>    I continue to invesgate this bug and find hypercall_mmu_update in
> qemu_remap_bucket(xc_map_foreign_bulk) is failing:
> 
> do_mmu_update
>       ->mod_l1_entry
>              ->  if ( !p2m_is_ram(p2mt) || unlikely(mfn == INVALID_MFN) )
>                          return -EINVAL;
> 
>    mfn==INVALID_MFN, because :
> 
> mod_l1_entry
>       ->gfn_to_mfn(p2m_get_hostp2m(pg_dom), l1e_get_pfn(nl1e), &p2mt));
>               ->p2m->get_entry
>                         ->p2m_gfn_to_mfn
>                                -> if ( gfn > p2m->max_mapped_pfn )
>                                    /* This pfn is higher than the
> highest the p2m map currently holds */
>                                    return _mfn(INVALID_MFN);
> 
>    The p2m->max_mapped_pfn is usually 0xfffff. In our case,
> mmu_update.val exceeds 0x8000000100000000.  Additionally, l1e =
> l1e_from_intpte(mmu_update.val); gfn=l1e_get_pfn(l1e ). Therefore, gfn
> will exceed 0xfffff.
> 
>    In the case of minios based stubdom, the mmu_update.vals do not
> exceed 0x8000000100000000. Next, I will invesgate why mmu_update.val
> exceeds 0x8000000100000000.

It looks like the address of the guest that qemu is trying to map is not
valid.
Make sure you are running a guest with less than 2GB of ram, otherwise
you need the patch series that Anthony sent on Friday:

http://marc.info/?l=qemu-devel&m=131074042905711&w=2

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