Re: with kerenl 2.6.27, CONFIG_KVM_GUEST does not work

[Held Bernhard <berny156@gmx.de>]

> Does the attached work for you?
> 
> 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;
>  }
This patch works for me (kvm-77, 2.6.27 host and guest)!

kvm-75 works fine, but kvm-76 and kvm-77 (all unpatched) show lot's of
segfaults in the guest (2.6.26.5 or 2.6.27, x86_64 on host and guest).

Thanks for the patch!

HTH,
Bernhard