On Tue, 26 Jul 2011, Jiageng Yu wrote:
> 2011/7/26 Jiageng Yu <yujiageng734@xxxxxxxxx>:
> > 2011/7/22 Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>:
> >> On Thu, 21 Jul 2011, Jiageng Yu wrote:
> >>> 2011/7/19 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 Fri Jul 08
> >>> >> >> >> 18:35:24 2011 +0100
> >>> >> >> >> +++ b/tools/firmware/hvmloader/hvmloader.c Fri Jul 15
> >>> >> >> >> 11:37:12 2011 +0000
> >>> >> >> >> @@ -430,7 +430,7 @@ int main(void)
> >>> >> >> >> bios->create_pir_tables();
> >>> >> >> >> }
> >>> >> >> >>
> >>> >> >> >> - if ( bios->load_roms )
> >>> >> >> >> + if ( 1 )
> >>> >> >> >> {
> >>> >> >> >> switch ( virtual_vga )
> >>> >> >> >> {
> >>> >> >> >>
> >>> >> >> >>
> >>> >> >> >
> >>> >> >> > 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,
> >>> >> >>
> >>> >> >> I find the cause of SIGSEGV signal:
> >>> >> >>
> >>> >> >> cpu_physical_memory_rw(target_phys_addr_t addr, uint8_t *buf, int
> >>> >> >> len, int is_write)
> >>> >> >> ->memcpy(buf, ptr + (addr & ~TARGET_PAGE_MASK),
> >>> >> >> l);
> >>> >> >>
> >>> >> >> In my case, ptr=0 and addr=0xc253e, when qemu attempts to vist
> >>> >> >> 0x53e address, the SIGSEGV signal is generated.
> >>> >> >>
> >>> >> >> 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
> >>>
> >>> Not this problem. I never alloc more than 2GB for the hvm guest. The
> >>> call stack in qemu is:
> >>>
> >>> qemu_get_ram_ptr
> >>> ->qemu_map_cache(addr, 0, 1)
> >>> -> if (!entry->vaddr_base || entry->paddr_index !=
> >>> address_index ||
> >>> !test_bit(address_offset >>
> >>> XC_PAGE_SHIFT, entry->valid_mapping)) {
> >>> qemu_remap_bucket(entry, size ? :
> >>> MCACHE_BUCKET_SIZE, address_index);
> >>> ->xc_map_foreign_bulk(xen_xc,
> >>> xen_domid, PROT_READ|PROT_WRITE,
> >>>
> >>> pfns, err, nb_pfn);
> >>>
> >>> The qemu tries to map pages from hvm guest(xen_domid) to linux
> >>> stubdom. But some hvm pages' pfns are larger than 0xfffff. So, in the
> >>> p2m_gfn_to_mfn, the judgement condition is valid:(p2m->max_mapped_pfn
> >>> = 0xfffff)
> >>>
> >>> if ( gfn > p2m->max_mapped_pfn )
> >>> /* This pfn is higher than the highest the p2m map currently
> >>> holds */
> >>> return _mfn(INVALID_MFN);
> >>>
> >>> In minios stubdom case, the hvm pages' pfns do not exceed 0xfffff.
> >>> Maybe the address translation in linux stubdom cause this probem?
> >>
> >> Trying to map a pfn > 0xfffff is clearly a mistake if the guest's memory
> >> does not exceed 2G:
> >>
> >> 0xfffff * 4096 > 2G
> >>
> >>
> >>> BTW, in minios stubdom case, there seems no hvmloader process. Is it
> >>> needed in linux stubdom?
> >>
> >> hvmloader is the first thing that runs within the guest, it is not a
> >> process in the stubdom or in dom0.
> >> It is required in both minios and linux stubdoms.
> >
> > Hi Stefano,
> >
> > I patched these patches, but we still have the same problem.
> > However, I noticed the qemu_get_ram_ptr(s->vram_offset) in
> > vga_common_init function was also failed. Maybe this can explain the
> > previous problem, which happened in the phase of trying to remap
> > 0xc0000-0xc8fff of hvm guest into stubdom.
> >
> > I have traced the process of qemu_get_ram_ptr(s->vram_offset) and
> > located the failure in p2m_gfn_to_mfn function:
> >
> > pod_retry_l3:
> > if ( (l3e_get_flags(*l3e) & _PAGE_PRESENT) == 0 )
> > {
> > .....
> > return _mfn(INVALID_MFN);
> > }
> >
> > I will continue to analyze this failure.
> >
> > Thanks!
> >
> > Jiageng Yu.
> >
>
>
> Hi,
>
> I compared the two executions of vga_common_init function in dom0
> and linux based stubdom. The former succeeded and the later was
> failed. First, they have the same call stack:
>
> Dom0 & Stubdom
> _________________________________________________________
> vga_common_init
> ->qemu_get_ram_ptr(s->vram_offset)
> ->block->host = xen_map_block(block->offset, block->length);
> ->xc_map_foreign_bulk()
> ->linux_privcmd_map_foreign_bulk()
> ->xen_remap_domain_mfn_range()
> ->HYPERVISOR_mmu_update()
> __________________________________________________________
>
> Xen
> __________________________________________________________
> do_mmu_update()
> ->case MMU_PT_UPDATE_PRESERVE_AD:
> ->case PGT_l1_page_table:
> ->mod_l1_entry(va, l1e, mfn,cmd == MMU_PT_UPDATE_PRESERVE_AD, v, pg_owner);
> ->mfn_x(gfn_to_mfn(p2m_get_hostp2m(pg_dom),
> l1e_get_pfn(nl1e), &p2mt));
> ->gfn_to_mfn_type_p2m()
> ->p2m->get_entry(p2m, gfn, t, &a, q);
> ->p2m_gfn_to_mfn(p2m,gfn,t,&a,q)
> ->if ( (l3e_get_flags(*l3e) &
> _PAGE_PRESENT) == 0 )
> -> Error happens!
>
> The qemu in dom0 can find the l3e of hvm guest, but the qemu in linux
> stubdom cannot find the l3e. In my case, s->vram_offset=0x40000000,
> vga_ram_size=0x800000. Therefore, we are going to map hvm guest's
> address area(pfn:0x40000, size:8M) into linux stubdom's address space.
>
> In p2m_gfn_to_mfn function, p2m->domain->domain_id=hvm guest,
> gfn=0x40000, t=p2m_mmio_dm.
> mfn = pagetable_get_mfn(p2m_get_pagetable(p2m) = 0x10746e;
> map_domain_page(mfn_x(mfn)) is also success. However, after executing:
> l3e += ( (0x40000 << PAGE_SHIFT) >> L3_PAGETABLE_SHIFT)
> the l3e->l3 =0 , and the error happens.
>
> So, in linux stubdom, when we are going to map the specified hvm
> guest's address(pfn:0x40000, size:8M), we find these pages of hvm
> guest are not present. This is never happened in qemu of dom0. Could
> you give me some prompts to this problem?
It seems that you are trying to map pages that don't exist.
The pages in question should be allocated by:
qemu_ram_alloc(NULL, "vga.vram", vga_ram_size)
qemu_ram_alloc_from_ptr
xen_ram_alloc
xc_domain_populate_physmap_exact
so I would add some printf and printk on this code path to find out if
xc_domain_populate_physmap_exact fails for some reasons._______________________________________________
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