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

[Greg Kurz <groug@kaod.org>]

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On Thu, 14 Sep 2017 13:17:48 +0200
Thomas Huth <thuth@redhat.com> wrote:

> On 14.09.2017 12:48, 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.  
> 
> By the way, what about the other CAPs that rely on hv_enabled? grepping
> through the QEMU sources, I can see:
> 
>  cap_ppc_smt = kvm_check_extension(s, KVM_CAP_PPC_SMT);
> 
>  cap_htab_fd = kvm_check_extension(s, KVM_CAP_PPC_HTAB_FD);
> 
>  int ret = kvm_check_extension(s, KVM_CAP_NR_VCPUS);
> 
>  return kvm_check_extension(kvm_state, KVM_CAP_SYNC_MMU);
> 
>  !kvm_check_extension(cs->kvm_state, KVM_CAP_SW_TLB)) {
> 
> ... do we need to fix them, too?
> 

I'm currently going through the KVM code to see which ones need to be
fixed. I'll send more patches shortly :)

Cheers,

--
Greg

>  Thomas


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