[Qemu-devel] [Bug] cirrus_vga: qemu abort at booting when configure vgamem_mb <= 2

[Qemu-devel] [Bug] cirrus_vga: qemu abort at booting when configure vgamem_mb <= 2

[Gonglei (Arei)]

Hi, Gerd

The issue consequentially occur, I have tested various qemu versions, 
including the current qemu.git. 

Any ideas? Thanks.

The command line:

./x86_64-softmmu/qemu-system-x86_64 -enable-kvm -m 4096 -smp 4 -name sles \ 
-boot c -drive file=/mnt/sdb/gonglei/image/sles.img -vnc 0.0.0.0:10 -monitor \
stdio -device cirrus-vga,id=video0,vgamem_mb=2 


The backtrace:

Program received signal SIGSEGV, Segmentation fault.
[Switching to Thread 0x7ffff2785700 (LWP 13966)]
0x00005555556ceb09 in cirrus_vga_mem_write (opaque=0x55555638e888, addr=0, mem_value=0, size=1) at hw/display/cirrus_vga.c:2039
2039                        *(s->vga.vram_ptr + bank_offset) = mem_value;
(gdb) bt
#0  0x00005555556ceb09 in cirrus_vga_mem_write (opaque=0x55555638e888, addr=0, mem_value=0, size=1) at hw/display/cirrus_vga.c:2039
#1  0x00005555558bc394 in memory_region_write_accessor (mr=0x55555639f5a8, addr=0, value=0x7ffff27848a8, size=1, shift=0, mask=255)
    at /mnt/sdb/gonglei/code/qemu/memory.c:441
#2  0x00005555558bc4d0 in access_with_adjusted_size (addr=0, value=0x7ffff27848a8, size=2, access_size_min=1, access_size_max=1, 
    access=0x5555558bc30b <memory_region_write_accessor>, mr=0x55555639f5a8) at /mnt/sdb/gonglei/code/qemu/memory.c:478
#3  0x00005555558bf331 in memory_region_dispatch_write (mr=0x55555639f5a8, addr=0, data=0, size=2)
    at /mnt/sdb/gonglei/code/qemu/memory.c:985
#4  0x00005555558c2b47 in io_mem_write (mr=0x55555639f5a8, addr=0, val=0, size=2) at /mnt/sdb/gonglei/code/qemu/memory.c:1744
#5  0x0000555555847c5b in address_space_rw (as=0x5555561e8600 <address_space_memory>, addr=655360, buf=0x7ffff7ff4030 "", len=2, 
    is_write=true) at /mnt/sdb/gonglei/code/qemu/exec.c:2029
#6  0x00005555558480c2 in cpu_physical_memory_rw (addr=655360, buf=0x7ffff7ff4030 "", len=2, is_write=1)
    at /mnt/sdb/gonglei/code/qemu/exec.c:2103
#7  0x00005555558b90c7 in cpu_physical_memory_write (addr=655360, buf=0x7ffff7ff4030, len=2)
    at /mnt/sdb/gonglei/code/qemu/include/exec/cpu-common.h:68
#8  0x00005555558b9025 in kvm_flush_coalesced_mmio_buffer () at /mnt/sdb/gonglei/code/qemu/kvm-all.c:1607
#9  0x0000555555844c08 in qemu_flush_coalesced_mmio_buffer () at /mnt/sdb/gonglei/code/qemu/exec.c:976
#10 0x00005555558bc34a in memory_region_write_accessor (mr=0x55555639f5a8, addr=170, value=0x7ffff2784b58, size=1, shift=0, mask=
    255) at /mnt/sdb/gonglei/code/qemu/memory.c:437
#11 0x00005555558bc4d0 in access_with_adjusted_size (addr=170, value=0x7ffff2784b58, size=2, access_size_min=1, access_size_max=1, 
    access=0x5555558bc30b <memory_region_write_accessor>, mr=0x55555639f5a8) at /mnt/sdb/gonglei/code/qemu/memory.c:478
#12 0x00005555558bf331 in memory_region_dispatch_write (mr=0x55555639f5a8, addr=170, data=0, size=2)
    at /mnt/sdb/gonglei/code/qemu/memory.c:985
#13 0x00005555558c2b47 in io_mem_write (mr=0x55555639f5a8, addr=170, val=0, size=2) at /mnt/sdb/gonglei/code/qemu/memory.c:1744
#14 0x0000555555847c5b in address_space_rw (as=0x5555561e8600 <address_space_memory>, addr=655530, buf=0x7ffff7ff2028 "", len=2, 
    is_write=true) at /mnt/sdb/gonglei/code/qemu/exec.c:2029
#15 0x00005555558480c2 in cpu_physical_memory_rw (addr=655530, buf=0x7ffff7ff2028 "", len=2, is_write=1)
    at /mnt/sdb/gonglei/code/qemu/exec.c:2103
#16 0x00005555558b940b in kvm_cpu_exec (cpu=0x5555562a7aa0) at /mnt/sdb/gonglei/code/qemu/kvm-all.c:1704
#17 0x0000555555838de2 in qemu_kvm_cpu_thread_fn (arg=0x5555562a7aa0) at /mnt/sdb/gonglei/code/qemu/cpus.c:873
#18 0x00007ffff59337f6 in start_thread () from /lib64/libpthread.so.0
#19 0x00007ffff568f09d in clone () from /lib64/libc.so.6
#20 0x0000000000000000 in ?? ()


Best regards,
-Gonglei

Re: [Qemu-devel] [Bug] cirrus_vga: qemu abort at booting when configure vgamem_mb <= 2

[Gerd Hoffmann]

On Fr, 2014-05-09 at 03:47 +0000, Gonglei (Arei) wrote:
> Hi, Gerd
> 
> The issue consequentially occur, I have tested various qemu versions, 
> including the current qemu.git. 

Missing sanity check.  It's not valid.  We mimic existing hardware here,
and the cirrus card emulated has 4 MB video memory.  So ideally we
should just use that and be done with it.  Problem is qemu has
historically used 8 or 16 mb vga memory for cirrus, and simply changing
it will break live migration.

So cirrus should accept 4 MB (correct value), 8 MB and 16 MB (for
backward compatibility) and reject everything else.  Patches are
welcome ;)

If you want reduce the qemu memory footprint use stdvga instead which
should handle memory sized from 1 MB to 256 MB just fine.

cheers,
  Gerd

Re: [Qemu-devel] [Bug] cirrus_vga: qemu abort at booting when configure vgamem_mb <= 2

[Gonglei (Arei)]

Hi,

> -----Original Message-----
> From: Gerd Hoffmann [mailto:kraxel@redhat.com]
> Sent: Friday, May 09, 2014 2:49 PM
> To: Gonglei (Arei)
> Cc: qemu-devel@nongnu.org
> Subject: Re: [Bug] cirrus_vga: qemu abort at booting when configure
> vgamem_mb <= 2
> 
> On Fr, 2014-05-09 at 03:47 +0000, Gonglei (Arei) wrote:
> > Hi, Gerd
> >
> > The issue consequentially occur, I have tested various qemu versions,
> > including the current qemu.git.
> 
> Missing sanity check.  It's not valid.  We mimic existing hardware here,
> and the cirrus card emulated has 4 MB video memory.  So ideally we
> should just use that and be done with it.  Problem is qemu has
> historically used 8 or 16 mb vga memory for cirrus, and simply changing
> it will break live migration.
> 
> So cirrus should accept 4 MB (correct value), 8 MB and 16 MB (for
> backward compatibility) and reject everything else.  Patches are
> welcome ;)
> 
Okay, I will add the check and post a patch. Thanks!

> If you want reduce the qemu memory footprint use stdvga instead which
> should handle memory sized from 1 MB to 256 MB just fine.
> 
It's OK.

> cheers,
>   Gerd
> 

Best regards,
-Gonglei