Re: with kerenl 2.6.27, CONFIG_KVM_GUEST does not work

[Xavier Gnata <xavier.gnata@gmail.com>]

Al Tobey wrote:
> On Sat, Oct 11, 2008 at 11:04 AM, Marcelo Tosatti <mtosatti@redhat.com> wrote:
>   
>> On Fri, Oct 10, 2008 at 06:11:08PM +0200, xming wrote:
>>     
>>> Kernel 2.6.27 + kvm-76 on the host really gives some performance boost here.
>>> but:
>>>
>>> When running 2.6.27 compiled with CONFIG_KVM_GUEST=y in the guest, the guest
>>> won't start, lot's of segfaults (in the guest)  especially udev initializations.
>>>
>>> unset CONFIG_KVM_GUEST=y, then the guest runs fine
>>>       
>> Does the attached work for you?
>>     
>
> I was running a bunch of VM's on kvm-75 (gentoo/intel x86_64/virtio
> guests) just fine.   I upgraded to kvm-77 this morning and the VM's
> failed to mount root read-write.    I checked the list before digging
> too deep and found a reference to this thread.   Adding this patch on
> top of stock kvm-77 appears to have fixed the issue.
>
> Thanks,
> -Al
>
>   
>> Avi, do you have thoughts on how to proceed with pvmmu? Using hypercalls
>> instead of faults can still be beneficial (for the first write before
>> page goes out of sync, or for non-leaf tables which currently don't go
>> oos). But at the current state pvmmu should be slower in most loads.
>> Perhaps disable it?
>>
>> KVM: MMU: sync root on paravirt TLB flush
>>
>> The pvmmu TLB flush handler should request a root sync, similarly to
>> a native read-write CR3.
>>
>> Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
>>
>> diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
>> index 79cb4a9..7e70e97 100644
>> --- a/arch/x86/kvm/mmu.c
>> +++ b/arch/x86/kvm/mmu.c
>> @@ -2747,6 +2747,7 @@ static int kvm_pv_mmu_write(struct kvm_vcpu *vcpu,
>>  static int kvm_pv_mmu_flush_tlb(struct kvm_vcpu *vcpu)
>>  {
>>        kvm_x86_ops->tlb_flush(vcpu);
>> +       set_bit(KVM_REQ_MMU_SYNC, &vcpu->requests);
>>        return 1;
>>  }
>>
>> --
>>
>>     

Ok I was patching the wrong file...sorry.
It works well with 2.6.27 (host and guest) and kvm-77

Xavier