Re: [Qemu-devel] [PATCH] ppc/kvm: use kvm_vm_check_extension() in kvmppc_is_pr()

[David Gibson <david@gibson.dropbear.id.au>]

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On Thu, Sep 14, 2017 at 12:48:04PM +0200, Greg Kurz wrote:
> If the host has both KVM PR and KVM HV loaded and we pass:
> 
> 	-machine pseries,accel=kvm,kvm-type=PR
> 
> the kvmppc_is_pr() returns false instead of true. Since the helper
> is mostly used as fallback, it doesn't have any real impact with
> recent kernels. A notable exception is the workaround to allow
> migration between compatible hosts with different PVRs (eg, POWER8
> and POWER8E), since KVM still doesn't provide a way to check if a
> specific PVR is supported (see commit c363a37a450f for details).
> 
> According to the official KVM API documentation [1], KVM_PPC_GET_PVINFO
> is "vm ioctl", but we check it as a global ioctl. The following function
> in KVM is hence called with kvm == NULL and considers we're in HV mode.
> 
> int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
> {
> 	int r;
> 	/* Assume we're using HV mode when the HV module is loaded */
> 	int hv_enabled = kvmppc_hv_ops ? 1 : 0;
> 
> 	if (kvm) {
> 		/*
> 		 * Hooray - we know which VM type we're running on. Depend on
> 		 * that rather than the guess above.
> 		 */
> 		hv_enabled = is_kvmppc_hv_enabled(kvm);
> 	}
> 
> Let's use kvm_vm_check_extension() to fix the issue.
> 
> [1] https://www.kernel.org/doc/Documentation/virtual/kvm/api.txt
> 
> Signed-off-by: Greg Kurz <groug@kaod.org>

Applied to ppc-for-2.11, good catch.

> ---
>  target/ppc/kvm.c |    2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/target/ppc/kvm.c b/target/ppc/kvm.c
> index 6442dfcb95b3..1deaf106d2b9 100644
> --- a/target/ppc/kvm.c
> +++ b/target/ppc/kvm.c
> @@ -120,7 +120,7 @@ static void kvm_kick_cpu(void *opaque)
>  static bool kvmppc_is_pr(KVMState *ks)
>  {
>      /* Assume KVM-PR if the GET_PVINFO capability is available */
> -    return kvm_check_extension(ks, KVM_CAP_PPC_GET_PVINFO) != 0;
> +    return kvm_vm_check_extension(ks, KVM_CAP_PPC_GET_PVINFO) != 0;
>  }
>  
>  static int kvm_ppc_register_host_cpu_type(void);
> 

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson

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