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

[Thomas Huth <thuth@redhat.com>]

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?

 Thomas