Re: [Qemu-devel] Open source qemu x86 accelerator module.

[James Stone <jmstone@dsl.pipex.com>]

Just a quick report on how this worked for me.

I am not using devfs or udev, and major device 222 is no longer valid
for /dev/qvm86.. I created the required device number 10.63

As expected, Win98 caused a segfault when using qvm86.

Here is the dmesg output:

qvm86: Created device 10.63
qvm86: Creating guest VM
esp:00002f7c 00082000 fec00000
Unable to handle kernel NULL pointer dereference at virtual address
00000000
 printing eip:
 e26144b0
 *pde = 00000000
 Oops: 0000 [#1]
 PREEMPT 
 Modules linked in: qvm86 realtime parport_pc lp parport ipt_REDIRECT
 ipt_owne       pt_LOG ipt_limit ipt_state ipt_multiport iptable_mangle
 ip_nat_irc ip_nat_ftp       table_nat ip_conntrack_irc ip_conntrack_ftp
 ip_conntrack emu10k1_gp snd_bt87x       ner bttv video_buf i2c_algo_bit
 v4l2_common btcx_risc tveeprom videodev nls_i       859_1 nls_cp437
 asb100 i2c_sensor i2c_nforce2 i2c_core usblp usb_storage viso
 sbserial sidewinder gameport joydev usbhid sg ide_cd cdrom n_hdlc
 ppp_synctty       p_generic slhc ehci_hcd ohci_hcd snd_virmidi
 snd_seq_virmidi snd_seq_oss snd_       _midi snd_seq_midi_event snd_seq
 snd_usb_audio snd_usb_lib usbcore snd_intel8       snd_emu10k1
 snd_rawmidi snd_seq_device snd_ac97_codec snd_pcm_oss snd_mixer_o
 snd_pcm snd_timer snd_page_alloc snd_util_mem snd_hwdep snd soundcore
 nvidia        gart forcedeth ipt_REJECT iptable_filter ip_tables
 CPU:    0
 EIP:    0060:[<e26144b0>]    Tainted: P      VLI
 EFLAGS: 00210286   (2.6.11.6) 
 EIP is at qvm86_flush_shadow+0xa0/0x160 [qvm86]
 eax: dd984000   ebx: 00005000   ecx: e2601000   edx: 00000000
 esi: 00000000   edi: 0000000c   ebp: 00005000   esp: dd985d80
 ds: 007b   es: 007b   ss: 0068
 Process qemu (pid: 4060, threadinfo=dd984000 task=d4303ae0)
 Stack: e2601000 046d423c 44a1423c 00000000 00000400 0000000c dd984000
 000003f
 00000001 36472eb9 dd985ebc c9b00000 e2601000 e2614ce4 e2601000
 36472eb
 00082000 fec00000 00000000 00000000 dd985e20 c01f7d36
 0036472e 000001b
 Call Trace:
 [<e2614ce4>] qvm86_exec+0x4b4/0x710 [qvm86]
 [<c01f7d36>] copy_from_user+0x46/0x90
 [<e261339c>] qvm86_linux_ioctl+0xdc/0x140 [qvm86]
 [<c0165eaf>] do_ioctl+0x6f/0xa0
 [<c01660f5>] vfs_ioctl+0x65/0x1d0
 [<c01662c7>] sys_ioctl+0x67/0xa0
 [<c01027db>] syscall_call+0x7/0xb
 Code: 8b 7c 24 14 89 dd 81 e5 00 f0 ff ff 8b 41 20
 8b 34 38 c7 44 24 1c ff 03        00 b8 00 e0 ff
 ff 21 e0 89 44 24 18 8d b6 00 00 00 00 <8b> 1e f6
 c3 01 75 17        06 00 00 00 00 83 c6 04 83 c5
 04 ff 4c 
 <6>qvm86: Device closed
		       

However, I noticed a significant speed up in performance in qemu
performance running win98 without the module installed.. Must be
something in the patch I suppose, but being somewhat clueless about
these things, I have no idea what. The speed up was in the order of
about 50%: Loading windows under qemu normally takes 30secs. With the
qvm86 patch, it took 20secs. Also performance was noticably more
snappy..

Very nice!

Keep up the good work!

James