Re: [PATCH] qemu-kvm: x86: Fix mismerge in cpu_post_load

[Jan Kiszka <jan.kiszka@web.de>]

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Gleb Natapov wrote:
> On Thu, Dec 03, 2009 at 07:21:01PM +0100, Jan Kiszka wrote:
>> Merge 8e2c5ec2f6 forgot to restore some qemu-kvm-specific hooks in
>> cpu_post_load. mp_state was readded later on, but tsc was missing,
>> breaking the guest timing after resume. Also, reset of halt was dropped
>> which is obviously required for in-kernel irqchip.
>>
>> Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
>> ---
>>
>> This solves "Problem 1" on my list.
>>
>> BTW, this patch just made me realize that the TSC MSR belongs to the
>> list states that should not be written back unconditionally. Upstream
>> does this currently, qemu-kvm not (at the price one more kvm-specific
>> hook into generic code). Unlike the other states we discussed, this one
>> is not "fixable" in the kernel. So I tend to think there is a real need
>> for my write-back scope abstraction - which would also be able to handle
>> the other states cleanly, both in upstream and here.
>>
>>  target-i386/machine.c |   10 +++++++++-
>>  1 files changed, 9 insertions(+), 1 deletions(-)
>>
>> diff --git a/target-i386/machine.c b/target-i386/machine.c
>> index 6bd447f..9ac477b 100644
>> --- a/target-i386/machine.c
>> +++ b/target-i386/machine.c
>> @@ -366,7 +366,15 @@ static int cpu_post_load(void *opaque, int version_id)
>>          hw_breakpoint_insert(env, i);
>>  
>>      tlb_flush(env, 1);
>> -    kvm_load_mpstate(env);
>> +
>> +    if (kvm_enabled()) {
>> +        /* when in-kernel irqchip is used, env->halted causes deadlock
>> +           because no userspace IRQs will ever clear this flag */
>> +        env->halted = 0;
>> +
> That is strange. env->halted should be used only for "info cpus" output
> in case of in-kernel irqchip. Can you see where it hangs?

This line was not directly involved in the regression I saw, it was just
the next one (load_tsc). But I simply restored qemu-kvm to the state
before the vmstate conversion merge, dropping only obviously unneeded
bits (namely the full register write-back).

The above line may no longer be required, but I wanted to play safe. If
you can explain which qemu-kvm change made this obsolete, please file a
removal patch!

> 
>> +        kvm_load_tsc(env);
>> +        kvm_load_mpstate(env);
>> +    }
>>  
>>      return 0;
>>  }
> 
> --
> 			Gleb.

Jan


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