[Xen-devel] Re: Linux Stubdom Problem

[Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>]

On Thu, 28 Jul 2011, Jiageng Yu wrote:
> 2011/7/27 Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>
> On Wed, 27 Jul 2011, Jiageng Yu wrote:
> > 2011/7/27 Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>:
> > > 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   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,
> > >> >>> >>
> > >> >>> >> Â ÂI continue to invesgate this bug and find hypercall_mmu_update 
> > >> >>> >> in
> > >> >>> >> qemu_remap_bucket(xc_map_foreign_bulk) is failing:
> > >> >>> >>
> > >> >>> >> do_mmu_update
> > >> >>> >> Â Â Â ->mod_l1_entry
> > >> >>> >> Â Â Â Â Â Â Â-> Âif ( !p2m_is_ram(p2mt) || unlikely(mfn == 
> > >> >>> >> INVALID_MFN) )
> > >> >>> >> Â Â Â Â Â Â Â Â Â Â Â Â Âreturn -EINVAL;
> > >> >>> >>
> > >> >>> >> Â Âmfn==INVALID_MFN, because :
> > >> >>> >>
> > >> >>> >> mod_l1_entry
> > >> >>> >> Â Â Â ->gfn_to_mfn(p2m_get_hostp2m(pg_dom), l1e_get_pfn(nl1e), 
> > >> >>> >> &p2mt));
> > >> >>> >> Â Â Â Â Â Â Â ->p2m->get_entry
> > >> >>> >> Â Â Â Â Â Â Â Â Â Â Â Â ->p2m_gfn_to_mfn
> > >> >>> >> Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â-> if ( gfn > p2m->max_mapped_pfn )
> > >> >>> >> Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â/* This pfn is higher than the
> > >> >>> >> highest the p2m map currently holds */
> > >> >>> >> Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Âreturn _mfn(INVALID_MFN);
> > >> >>> >>
> > >> >>> >> Â ÂThe p2m->max_mapped_pfn is usually 0xfffff. In our case,
> > >> >>> >> mmu_update.val exceeds 0x8000000100000000. ÂAdditionally, l1e =
> > >> >>> >> l1e_from_intpte(mmu_update.val); gfn=l1e_get_pfn(l1e ). 
> > >> >>> >> Therefore, gfn
> > >> >>> >> will exceed 0xfffff.
> > >> >>> >>
> > >> >>> >> Â ÂIn 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
> > >> >>> Â Â Â ->qemu_map_cache(addr, 0, 1)
> > >> >>> Â Â Â Â Â Â Â Â Â-> if (!entry->vaddr_base || entry->paddr_index !=
> > >> >>> address_index ||
> > >> >>> Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â !test_bit(address_offset >>
> > >> >>> XC_PAGE_SHIFT, entry->valid_mapping)) {
> > >> >>> Â Â Â Â Â Â Â Â Â Â Â Â Â Âqemu_remap_bucket(entry, size ? :
> > >> >>> MCACHE_BUCKET_SIZE, address_index);
> > >> >>> Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â->xc_map_foreign_bulk(xen_xc,
> > >> >>> xen_domid, PROT_READ|PROT_WRITE,
> > >> >>>
> > >> >>> Â Â Â Â Â Â Â Â 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)
> > >> >>>
> > >> >>> Â Â if ( gfn > p2m->max_mapped_pfn )
> > >> >>> Â Â Â Â /* This pfn is higher than the highest the p2m map currently 
> > >> >>> holds */
> > >> >>> Â Â Â Â return _mfn(INVALID_MFN);
> > >> >>>
> > >> >>> ÂIn 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
> > >> >>
> > >> >>
> > >> >>> ÂBTW, 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,
> > >> >
> > >> > Â Â ÂI 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.
> > >> >
> > >> > Â Â I have traced the process of qemu_get_ram_ptr(s->vram_offset) and
> > >> > located the failure in p2m_gfn_to_mfn function:
> > >> >
> > >> > Â Â pod_retry_l3:
> > >> > Â Â Â Âif ( (l3e_get_flags(*l3e) & _PAGE_PRESENT) == 0 )
> > >> > Â Â Â Â{
> > >> > Â Â Â Â Â Â Â Â .....
> > >> > Â Â Â Â Â Â Â Â return _mfn(INVALID_MFN);
> > >> > Â Â Â Â}
> > >> >
> > >> > Â Â I will continue to analyze this failure.
> > >> >
> > >> > Â Â Thanks!
> > >> >
> > >> > Jiageng Yu.
> > >> >
> > >>
> > >>
> > >> Hi,
> > >>
> > >> Â Â 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
> > >> Â Â Â->qemu_get_ram_ptr(s->vram_offset)
> > >> Â Â Â Â Â Â->block->host = xen_map_block(block->offset, block->length);
> > >> Â Â Â Â Â Â Â Â Â->xc_map_foreign_bulk()
> > >> Â Â Â Â Â Â Â Â Â Â Â Â ->linux_privcmd_map_foreign_bulk()
> > >> Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â->xen_remap_domain_mfn_range()
> > >> Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â->HYPERVISOR_mmu_update()
> > >> __________________________________________________________
> > >>
> > >> Xen
> > >> __________________________________________________________
> > >> do_mmu_update()
> > >> Â Â->case MMU_PT_UPDATE_PRESERVE_AD:
> > >> Â Â->case PGT_l1_page_table:
> > >> Â Â->mod_l1_entry(va, l1e, mfn,cmd == MMU_PT_UPDATE_PRESERVE_AD, v, 
> > >> pg_owner);
> > >> Â Â Â Â Â ->mfn_x(gfn_to_mfn(p2m_get_hostp2m(pg_dom),
> > >> l1e_get_pfn(nl1e), &p2mt));
> > >> Â Â Â Â Â Â Â Â Â->gfn_to_mfn_type_p2m()
> > >> Â Â Â Â Â Â Â Â Â Â Â Â ->p2m->get_entry(p2m, gfn, t, &a, q);
> > >> Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â->p2m_gfn_to_mfn(p2m,gfn,t,&a,q)
> > >> Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â ->if ( (l3e_get_flags(*l3e) &
> > >> _PAGE_PRESENT) == 0 )
> > >> Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â -> Â ÂError 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)
> > > Â Âqemu_ram_alloc_from_ptr
> > > Â Â Â Âxen_ram_alloc
> > > Â Â Â Â Â Âxc_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.
> >
> > Hmm.. the linux stubdom kernel had a wrong p2m pair
> > <gfn(0x40000),mfn(0x127bd2)> for some reason. But next, the
> > xc_domain_populate_physmap_exact will setup the correct p2m pair
> > <gfn(0x40000),mfn(0x896b7)>. However, the p2m pair in stubdom kernel
> > has not been updated, because the fllowing access to 0x40000 still
> > uses 0x127bd2.
> 
> The p2m for the guest domain is only one in Xen, so I cannot understand
> how it is possible that you get the old mfn value.
> Also there shouldn't even be an old value because before
> xc_domain_populate_physmap_exact pfn 0x40000 wasn't even allocated in
> the guest yet.
> 
> Make sure you are using the right domid in both calls
> (xc_domain_populate_physmap_exact and xc_map_foreign_bulk), also make
> sure that libxenlight calls xc_domain_set_target and xs_set_target for
> the stubdom otherwise the stubdom is not going to be privileged enough
> to allocate and map memory of the guest.
> 
> 
> > I notice you have a patch: xen: modify kernel mappings corresponding
> > to granted pages. I think maybe it could slove my problem.
> 
> That patch fixes a different issue, related to grant table mappings.
> 
> 
> Â
> OK. That is my fault.
> Â
> The root cause of previous problem is that the backend drivers in qemu are 
> not stopped. To confirm this root cause,
> I try to erase the codes about stubdom in xen_be_init function of old qemu. 
> The same problem appears. The following
> patch is to fix this issue in upstream qemu.
> Â
> diff --git a/xen-all.c b/xen-all.c
> index b73fc43..8f0645e 100644
> --- a/xen-all.c
> +++ b/xen-all.c
> @@ -472,12 +479,23 @@ static void cpu_handle_ioreq(void *opaque)
> Âstatic void xenstore_record_dm_state(XenIOState *s, const char *state)
> Â{
> ÂÂÂÂ char path[50];
> +#ifdef CONFIG_STUBDOM
> +ÂÂÂ s->xenstore = xs_daemon_open();
> +ÂÂÂ if (s->xenstore == NULL) {
> +ÂÂÂÂÂÂÂ perror("xen: xenstore open");
> +ÂÂÂÂÂÂÂ return -errno;
> +ÂÂÂ }
> +#endif
> ÂÂÂÂ snprintf(path, sizeof (path), "/local/domain/0/device-model/%u/state", 
> xen_domid);
> ÂÂÂÂ if (!xs_write(s->xenstore, XBT_NULL, path, state, strlen(state))) {
> ÂÂÂÂÂÂÂÂ fprintf(stderr, "error recording dm state\n");
> ÂÂÂÂÂÂÂÂ exit(1);
> ÂÂÂÂ }
> +#ifdef CONFIG_STUBDOM
> +ÂÂÂ xs_daemon_close(s->xenstore);
> +ÂÂÂ s->xenstore = NULL;
> +#endif
> Â}

Why do you need to re-open the xenstore connection here?
It should be already been opened by xen_hvm_init, like in the normal
case.


> Âstatic void xen_main_loop_prepare(XenIOState *state)
> @@ -538,6 +556,7 @@ int xen_hvm_init(void)
> Â
> ÂÂÂÂ state = qemu_mallocz(sizeof (XenIOState));
> Â
> +#ifndef CONFIG_STUBDOM
> ÂÂÂÂ state->xce_handle = xen_xc_evtchn_open(NULL, 0);
> ÂÂÂÂ if (state->xce_handle == XC_HANDLER_INITIAL_VALUE) {
> ÂÂÂÂÂÂÂÂ perror("xen: event channel open");
> @@ -549,6 +568,10 @@ int xen_hvm_init(void)
> ÂÂÂÂÂÂÂÂ perror("xen: xenstore open");
> ÂÂÂÂÂÂÂÂ return -errno;
> ÂÂÂÂ }
> +#else
> +ÂÂÂ state->xce_handle = XC_HANDLER_INITIAL_VALUE;
> +ÂÂÂ state->xenstore = NULL;
> +#endif
> Â

So you are explicitly avoiding to open the xenstore connection from
xen_hvm_init, why?
I think you might be trying to fix a race condition, maybe something is
not ready yet at this point that becomes ready later?


> ÂÂÂÂ state->exit.notify = xen_exit_notifier;
> ÂÂÂÂ qemu_add_exit_notifier(&state->exit);
> @@ -575,9 +598,10 @@ int xen_hvm_init(void)
> Â
> ÂÂÂÂ state->ioreq_local_port = qemu_mallocz(smp_cpus * sizeof 
> (evtchn_port_t));
> Â
> ÂÂÂÂ /* FIXME: how about if we overflow the page here? */
> ÂÂÂÂ for (i = 0; i < smp_cpus; i++) {
> -ÂÂÂÂÂÂÂ rc = xc_evtchn_bind_interdomain(state->xce_handle, xen_domid,
> +ÂÂÂÂÂÂÂrc = xc_evtchn_bind_interdomain(xen_xc, xen_domid,
> ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ xen_vcpu_eport(state->shared_page, 
> i));
> ÂÂÂÂÂÂÂÂ if (rc == -1) {
> ÂÂÂÂÂÂÂÂÂÂÂÂ fprintf(stderr, "bind interdomain ioctl error %d\n", errno);
> 

This cannot be right: xc_evtchn_bind_interdomain takes a xc_evtchn* as
first paramter while xen_xc is xc_interface*
This change would prevent you from receiving any IO request
notifications from Xen.

 
> The new problem is my stubdom hangs at:
> Â
> hvmloader:
> ÂÂÂÂ ->main()
> ÂÂÂÂÂÂÂÂÂÂÂ ->pci_setup()
> ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ ->pci_writeb(PCI_ISA_DEVFN, 0x60 + link, isa_irq);
> Â
> I am investigating this problem. The pci_writeb will finally call the 
> hvm_set_pci_link_route in Xen:
> Â
> hvmloader:ÂÂÂÂÂÂÂÂÂÂÂÂÂpci_writeb(PCI_ISA_DEVFN, 0x60 + link, isa_irq);
> qemu(stubdom):ÂÂÂÂ PCIHostState->data_handler->write()
> qemu(stubdom):ÂÂÂÂ i440fx_write_config_xen()
> qemu(stubdom):ÂÂÂÂÂxen_piix_pci_write_config_client()
> xenctrl:ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂxc_hvm_set_pci_link_route()
> Â
> The ioport is registered by pci_host_data_register_ioport(0xcfc, s) function.
> Â
> I will find out why not invoke i440fx_write_config_xen() in my case. I will 
> also read the pciutils.patch of minios stubdom
> and maybe find something interesting.
 
I think you are not receiving any IO request notifications from Xen
because of the previous change.
It is probably worth adding a printf into xen-all.c:handle_ioreq to see
if you receive something.

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