Re: [RFC v2 0/1] memory: Delete assertion in memory_region_unregister_iommu_notifier

[Eugenio Perez Martin]

On Mon, Jun 29, 2020 at 5:05 PM Paolo Bonzini <pbonzini@redhat.com> wrote:
>
> On 26/06/20 08:41, Eugenio Pérez wrote:
> > If we examinate *entry in frame 4 of backtrace:
> > *entry = {target_as = 0x555556f6c050, iova = 0x0, translated_addr = 0x0,
> > addr_mask = 0xffffffffffffffff, perm = 0x0}
> >
> > Which (I think) tries to invalidate all the TLB registers of the device.
> >
> > Just deleting that assert is enough for the VM to start and communicate
> > using IOMMU, but maybe a better alternative is possible. We could move
> > it to the caller functions in other cases than IOMMU invalidation, or
> > make it conditional only if not invalidating.
>
> Yes, I think moving it up in the call stack is better. I cannot say
> where because the backtrace was destroyed by git (due to lines starting
> with "#").
>

Ouch, what a failure!

Pasting here for completion, sorry!

(gdb) bt
#0  0x00007ffff521370f in raise () at /lib64/libc.so.6
#1  0x00007ffff51fdb25 in abort () at /lib64/libc.so.6
#2  0x00007ffff51fd9f9 in _nl_load_domain.cold.0 () at /lib64/libc.so.6
#3  0x00007ffff520bcc6 in .annobin_assert.c_end () at /lib64/libc.so.6
#4  0x0000555555888171 in memory_region_notify_one
(notifier=0x7ffde0487fa8, entry=0x7ffde5dfe200) at
/home/qemu/memory.c:1918
#5  0x0000555555888247 in memory_region_notify_iommu
(iommu_mr=0x555556f6c0b0, iommu_idx=0, entry=...) at
/home/qemu/memory.c:1941
#6  0x0000555555951c8d in vtd_process_device_iotlb_desc
(s=0x555557609000, inv_desc=0x7ffde5dfe2d0)
    at /home/qemu/hw/i386/intel_iommu.c:2468
#7  0x0000555555951e6a in vtd_process_inv_desc (s=0x555557609000) at
/home/qemu/hw/i386/intel_iommu.c:2531
#8  0x0000555555951fa5 in vtd_fetch_inv_desc (s=0x555557609000) at
/home/qemu/hw/i386/intel_iommu.c:2563
#9  0x00005555559520e5 in vtd_handle_iqt_write (s=0x555557609000) at
/home/qemu/hw/i386/intel_iommu.c:2590
#10 0x0000555555952b45 in vtd_mem_write (opaque=0x555557609000,
addr=136, val=2688, size=4) at /home/qemu/hw/i386/intel_iommu.c:2837
#11 0x0000555555883e17 in memory_region_write_accessor
    (mr=0x555557609330, addr=136, value=0x7ffde5dfe478, size=4,
shift=0, mask=4294967295, attrs=...) at /home/qemu/memory.c:483
#12 0x000055555588401d in access_with_adjusted_size
    (addr=136, value=0x7ffde5dfe478, size=4, access_size_min=4,
access_size_max=8, access_fn=
    0x555555883d38 <memory_region_write_accessor>, mr=0x555557609330,
attrs=...) at /home/qemu/memory.c:544
#13 0x0000555555886f37 in memory_region_dispatch_write
(mr=0x555557609330, addr=136, data=2688, op=MO_32, attrs=...)
    at /home/qemu/memory.c:1476
#14 0x0000555555827a03 in flatview_write_continue
    (fv=0x7ffdd8503150, addr=4275634312, attrs=...,
ptr=0x7ffff7ff0028, len=4, addr1=136, l=4, mr=0x555557609330) at
/home/qemu/exec.c:3146
#15 0x0000555555827b48 in flatview_write (fv=0x7ffdd8503150,
addr=4275634312, attrs=..., buf=0x7ffff7ff0028, len=4)
    at /home/qemu/exec.c:3186
#16 0x0000555555827e9d in address_space_write
    (as=0x5555567ca640 <address_space_memory>, addr=4275634312,
attrs=..., buf=0x7ffff7ff0028, len=4) at /home/qemu/exec.c:3277
#17 0x0000555555827f0a in address_space_rw
    (as=0x5555567ca640 <address_space_memory>, addr=4275634312,
attrs=..., buf=0x7ffff7ff0028, len=4, is_write=true)
    at /home/qemu/exec.c:3287
#18 0x000055555589b633 in kvm_cpu_exec (cpu=0x555556b65640) at
/home/qemu/accel/kvm/kvm-all.c:2511
#19 0x0000555555876ba8 in qemu_kvm_cpu_thread_fn (arg=0x555556b65640)
at /home/qemu/cpus.c:1284
#20 0x0000555555dafff1 in qemu_thread_start (args=0x555556b8c3b0) at
util/qemu-thread-posix.c:521
#21 0x00007ffff55a62de in start_thread () at /lib64/libpthread.so.0
#22 0x00007ffff52d7e83 in clone () at /lib64/libc.so.6

(gdb) frame 4
#4  0x0000555555888171 in memory_region_notify_one
(notifier=0x7ffde0487fa8, entry=0x7ffde5dfe200) at
/home/qemu/memory.c:1918
1918        assert(entry->iova >= notifier->start && entry_end <=
notifier->end);
(gdb) p *entry
$1 = {target_as = 0x555556f6c050, iova = 0, translated_addr = 0,
addr_mask = 18446744073709551615, perm = IOMMU_NONE}

Thanks!

> Paolo
>
> > Any comment would be appreciated. Thanks!
> >
> > Guest kernel version: kernel-3.10.0-1151.el7.x86_64
> >
> > Bug reference: https://bugs.launchpad.net/qemu/+bug/1885175
> >
> > v2: Actually delete assertion instead of just commenting out using C99
> >
> > Eugenio Pérez (1):
> >   memory: Delete assertion in memory_region_unregister_iommu_notifier
> >
> >  memory.c | 2 --
> >  1 file changed, 2 deletions(-)
> >
>