Re: [Qemu-devel] VM can not boot after commit 235e898

[Dunrong Huang]

On Wed, Jun 5, 2013 at 10:44 AM, Dunrong Huang <address@hidden> wrote:

On Wed, Jun 5, 2013 at 1:03 AM, Jordan Justen <address@hidden> wrote:

On Tue, Jun 4, 2013 at 1:26 AM, Dunrong Huang <address@hidden> wrote:
> On Tue, Jun 4, 2013 at 3:51 PM, Gleb Natapov <address@hidden> wrote:
>> On Tue, Jun 04, 2013 at 03:47:47PM +0800, Dunrong Huang wrote:
>> > On Tue, Jun 4, 2013 at 2:47 PM, Paolo Bonzini <address@hidden>
>> > wrote:
>> >
>> > > Il 04/06/2013 05:47, Dunrong Huang ha scritto:
>> > > >
>> > > > QEMU command:
>> > > > ~/usr/bin/qemu-system-x86_64 -enable-kvm -m 1024 debian-append.img
>> > > >
>> > > > git bisect tells that the following commit causes this bug:
>> > > >
>> > > > commit 235e8982ad393e5611cb892df54881c872eea9e1
>> > > > Author: Jordan Justen <address@hidden
>> > > > <mailto:address@hidden>>
>> > > > Date:   Wed May 29 01:27:26 2013 -0700
>> > > >
>> > > >     kvm: support using KVM_MEM_READONLY flag for regions
>> > > >
>> > > >     For readonly memory regions and rom devices in romd_mode,
>> > > >     we make use of the KVM_MEM_READONLY. A slot that uses
>> > > >     KVM_MEM_READONLY can be read from and code can execute from the
>> > > >     region, but writes will exit to qemu.
>> > > >
>> > > > After reverting this commit, VM can boot normally.
>> > >
>> > > A patch is queued for that.  Using kernel 3.8 or reverting the commit
>> > > will both work.
>> > >
>> > Ok, thanks for information, I will try it.
>> >
>> The fix is 651eb0f4 and you claim it is still fails for you. This is
>> strange because the commit fixed the problem for everyone else. Can you
>> double check that you are testing the right commit and you recompiled
>> and reinstalled?
>
>
> I am sure 651eb0f4 does not fix this problem.
>
> My test environment is below:
>
> * config.log:
> # head -n 2 config.log
> # QEMU configure log 2013年 06月 04日 星期二 16:12:59 CST
> # Configured with: './configure' '--prefix=/root/usr' '--enable-kvm'
> '--enable-werror' '--enable-debug' '--enable-debug-tcg'
> '--enable-debug-info' '--enable-sdl' '--enable-gtk' '--enable-virtfs'
> '--enable-vnc' '--enable-mixemu' '--enable-vnc-tls' '--enable-vnc-sasl'
> '--enable-vnc-jpeg' '--enable-vnc-png' '--enable-vnc-ws' '--enable-curses'
> '--enable-curl' '--enable-nptl' '--enable-system' '--enable-user'
> '--enable-linux-user' '--enable-guest-base' '--enable-uuid' '--enable-vde'
> '--enable-linux-aio' '--enable-cap-ng' '--enable-attr' '--enable-docs'
> '--enable-vhost-net' '--enable-spice' '--enable-usb-redir'
> '--enable-smartcard-nss' '--enable-tpm' '--enable-guest-agent'
> '--target-list=x86_64-softmmu'
>
> * kernel version:
> # uname -a
> Linux gentoo-company 3.8.2-gentoo #1 SMP Fri Mar 8 11:44:36 CST 2013 x86_64
> Intel(R) Core(TM)2 Duo CPU E7500 @ 2.93GHz GenuineIntel GNU/Linux

You were using a >3.8 kernel originally? (Someone mentioned trying a
3.8 kernel, and I think that is when you went to 3.8.)

yes, I have been using kernel 3.8.2 lately, not because of Paolo's suggestion.

> * details of git tree:
> # git log HEAD --oneline
> 1713924 gtk: don't use g_object_unref on GdkCursor
> 41686a9 gtk: don't resize window when enabling scaling
> 651eb0f fix double free the memslot in kvm_set_phys_mem
> 25b4833 configure: Report unknown target names more helpfully
> 6e92f82 configure: Autogenerate default target list
> 0ded1fe Merge remote-tracking branch 'pmaydell/arm-devs.next' into staging
> 95669e6 i.MX: Improve EPIT timer code.
> 6539ed2 exynos4210.c: register rom_mem for memory migration
>
>
> * QEMU command line:
> x86_64-softmmu/qemu-system-x86_64 -enable-kvm -cdrom
> /mnt/nfs/Images/ISO/ubuntu-12.04-dvd-amd64.iso

FWIW, I've been able to boot the 11.10 iso when booted to a 3.9 kernel.

Does it only fail after you boot the OS? If you just run KVM without a
disk, so only seabios runs, is it okay?

 

It fails even runing without any parameters, like:

x86_64-softmmu/qemu-system-x86_64 -enable-kvm

No BIOS information printed, just a black screen is shown.

> After disable KVM_MEM_READONLY flag like below, VM can boot normally.
> diff --git a/kvm-all.c b/kvm-all.c
> index 405480e..c33ba6e 100644
> --- a/kvm-all.c
> +++ b/kvm-all.c
> @@ -774,7 +774,7 @@ static void kvm_set_phys_mem(MemoryRegionSection
> *section, bool add)
>      mem->memory_size = size;
>      mem->start_addr = start_addr;
>      mem->ram = ram;
> -    mem->flags = kvm_mem_flags(s, log_dirty, readonly_flag);
> +    mem->flags = kvm_mem_flags(s, log_dirty, false);
>
>      err = kvm_set_user_memory_region(s, mem);
>      if (err) {
>
> I can provide more details if needed.

I don't think you mentioned how it fails. Does KVM crash? Is an error
message printed? Does the VM reset, or just hang?

No QEMU or kvm crashes, no error message printed, I mean it just hangs, even no BIOS information are printed.

And "top" shows QEMU consumes 100% cpu.

When I define DEBUG_KVM in kvm-all.c, and run QEMU(this time I boot a normal OS disk), 

# x86_64-softmmu/qemu-system-x86_64 -enable-kvm -hda /mnt/nfs/Images/debian-append.img

kvm_init_vcpu

kvm_cpu_exec()

handle_io

handle_io

handle_io

handle_io

Only 4 debug messages(handle_io) are printed, then nothing is shown, and "top" shows QEMU process uses 100% CPU.

Another strange thing is that VM can boot normally on my laptop(with a gentoo kernel 3.8.1 installed and same QEMU binary).

So I suspect the kernel is the root cause of this problem. I will try again after upgrading kernel to 3.9.

After upgrading kernel from 3.8.2 to 3.9.4, this problem goes way. So this bug must have been fixed in kernel 3.9. 

Thank you all for replies! 

-Jordan

--

Best Regards,

Dunrong Huang 

Homepage: http://mathslinux.org