Re: Windows fails to boot after rebase to QEMU master

["Dr. David Alan Gilbert" <dgilbert@redhat.com>]

* Michael S. Tsirkin (mst@redhat.com) wrote:
> On Fri, May 21, 2021 at 11:17:19AM +0200, Siddharth Chandrasekaran wrote:
> > After a rebase to QEMU master, I am having trouble booting windows VMs.
> > Git bisect indicates commit f5cc5a5c1686 ("i386: split cpu accelerators
> > from cpu.c, using AccelCPUClass") to have introduced the issue. I spent
> > some time looking at into it yesterday without much luck.
> > 
> > Steps to reproduce:
> > 
> >     $ ./configure --enable-kvm --disable-xen --target-list=x86_64-softmmu --enable-debug
> >     $ make -j `nproc`
> >     $ ./build/x86_64-softmmu/qemu-system-x86_64 \
> >         -cpu host,hv_synic,hv_vpindex,hv_time,hv_runtime,hv_stimer,hv_crash \
> >         -enable-kvm \
> >         -name test,debug-threads=on \
> >         -smp 1,threads=1,cores=1,sockets=1 \
> >         -m 4G \
> >         -net nic -net user \
> >         -boot d,menu=on \
> >         -usbdevice tablet \
> >         -vnc :3 \
> >         -machine q35,smm=on \
> >         -drive if=pflash,format=raw,readonly=on,unit=0,file="../OVMF_CODE.secboot.fd" \
> >         -drive if=pflash,format=raw,unit=1,file="../OVMF_VARS.secboot.fd" \
> >         -global ICH9-LPC.disable_s3=1 \
> >         -global driver=cfi.pflash01,property=secure,value=on \
> >         -cdrom "../Windows_Server_2016_14393.ISO" \
> >         -drive file="../win_server_2016.qcow2",format=qcow2,if=none,id=rootfs_drive \
> >         -device ahci,id=ahci \
> >         -device ide-hd,drive=rootfs_drive,bus=ahci.0
> > 
> > If the issue is not obvious, I'd like some pointers on how to go about
> > fixing this issue.
> > 
> > ~ Sid.
> > 
> 
> At a guess this commit inadvertently changed something in the CPU ID.
> I'd start by using a linux guest to dump cpuid before and after the
> change.

I've not had a chance to do that yet, however I did just end up with a
bisect of a linux guest failure bisecting to the same patch:

[dgilbert@dgilbert-t580 qemu]$ git bisect bad
f5cc5a5c168674f84bf061cdb307c2d25fba5448 is the first bad commit
commit f5cc5a5c168674f84bf061cdb307c2d25fba5448
Author: Claudio Fontana <cfontana@suse.de>
Date:   Mon Mar 22 14:27:40 2021 +0100

    i386: split cpu accelerators from cpu.c, using AccelCPUClass
    
    i386 is the first user of AccelCPUClass, allowing to split
    cpu.c into:
    
    cpu.c            cpuid and common x86 cpu functionality
    host-cpu.c       host x86 cpu functions and "host" cpu type
    kvm/kvm-cpu.c    KVM x86 AccelCPUClass
    hvf/hvf-cpu.c    HVF x86 AccelCPUClass
    tcg/tcg-cpu.c    TCG x86 AccelCPUClass
    

The guest crash is:
[   85.008985][ T1524] BUG: unable to handle page fault for address: ffffffff810d9c42
[   85.012868][ T1524] #PF: supervisor write access in kernel mode
[   85.012962][ T1524] #PF: error_code(0x0003) - permissions violation
[   85.013043][ T1524] PGD 2224067 P4D 2224067 PUD 2225063 PMD 10001e1 
[   85.013180][ T1524] Oops: 0003 [#1] SMP NOPTI
[   85.013295][ T1524] CPU: 2 PID: 1524 Comm: blogbench Not tainted 5.11.0-rc7 #100
[   85.013395][ T1524] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.14.0-0-g155821a1990b-prebuilt.qemu.org 04/01/2014
[   85.013546][ T1524] RIP: 0010:kvm_kick_cpu+0x22/0x30
[   85.013630][ T1524] Code: 0f 1f 84 00 00 00 00 00 55 48 63 ff 48 c7 c0 78 11 01 00 48 8b 14 fd c0 36 11 82 48 89 e5 53 31 db 0f b7 0c 02 b8 05 00 00 00 <0f> 01 d9 5b 5d c3 0f 1f 84 00 00 00 00 00 55 48 89 e5 53 48 89 fb
[   85.013852][ T1524] RSP: 0018:ffffc90000747c08 EFLAGS: 00010046
[   85.013951][ T1524] RAX: 0000000000000005 RBX: 0000000000000000 RCX: 0000000000000000
[   85.014058][ T1524] RDX: ffff88807c600000 RSI: 0000000000000100 RDI: 0000000000000000
[   85.014153][ T1524] RBP: ffffc90000747c10 R08: ffff88807c72a800 R09: ffff88807ffd6000
[   85.014248][ T1524] R10: 0000000000000001 R11: 0000000000000046 R12: ffff88807c72a800
[   85.014343][ T1524] R13: 0000000000000000 R14: ffff888005409940 R15: ffff88807c72a818
[   85.014437][ T1524] FS:  00007fa2f750a700(0000) GS:ffff88807c700000(0000) knlGS:0000000000000000
[   85.014559][ T1524] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[   85.014644][ T1524] CR2: ffffffff810d9c42 CR3: 0000000009016003 CR4: 0000000000370ea0
[   85.014741][ T1524] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[   85.014842][ T1524] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[   85.014945][ T1524] Call Trace:
[   85.014998][ T1524]  __pv_queued_spin_unlock_slowpath+0xa0/0xd0
[   85.015103][ T1524]  __raw_callee_save___pv_queued_spin_unlock_slowpath+0x15/0x24
[   85.015206][ T1524]  .slowpath+0x9/0x15
[   85.015261][ T1524]  do_raw_spin_unlock+0x48/0xc0
[   85.015333][ T1524]  _raw_spin_unlock_irq+0x1d/0x30
[   85.015404][ T1524]  finish_task_switch+0xcc/0x2c0
[   85.015478][ T1524]  __schedule+0x283/0x9a0
[   85.015534][ T1524]  schedule+0x50/0xc0
[   85.015588][ T1524]  request_wait_answer+0x126/0x240
[   85.015667][ T1524]  ? finish_wait+0x90/0x90
[   85.015740][ T1524]  fuse_simple_request+0x17c/0x2e0

the backtrace moves about a bit, but it always ends up as
a page fault in kvm_kick_cpu.

My qemu commandline being:
./x86_64-softmmu/qemu-system-x86_64 -M pc,memory-backend=mem,accel=kvm -cpu host  -m 2G,maxmem=16G,slots=16 -smp 4 -object memory-backend-memfd,id=mem,size=2G,share=on -chardev socket,id=char0,path=/tmp/vhostqemu -device vhost-user-fs-pci,queue-size=1024,chardev=char0,tag=myfs -kernel /home/dgilbert/virtio-fs/kernel-builds/monolithic-dax-20210209a -initrd /home/dgilbert/virtio-fs/test-initramfs.img -chardev stdio,mux=on,id=mon -mon chardev=mon,mode=readline  -device virtio-serial-pci,disable-modern=on -device virtconsole,chardev=mon -object rng-random,id=objrng0,filename=/dev/urandom -device virtio-rng-pci,rng=objrng0,id=rng0,disable-legacy=on -vga none -append "console=hvc0  debug loglevel=9 systemd.journald.forward_to_console" -display none  -overcommit mem-lock=off -netdev user,id=usernet -device virtio-net-pci,netdev=usernet -name debug-threads=on


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> 
-- 
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK