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KVM: x86: fix backward migration with async_PF

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Guests on new hypersiors might set KVM_ASYNC_PF_DELIVERY_AS_PF_VMEXIT
bit when enabling async_PF, but this bit is reserved on old hypervisors,
which results in a failure upon migration.

To avoid breaking different cases, we are checking for CPUID feature bit
before enabling the feature and nothing else.

Fixes: 52a5c155cf ("KVM: async_pf: Let guest support delivery of async_pf from guest mode")
Cc: <stable@vger.kernel.org>
Reviewed-by: Wanpeng Li <wanpengli@tencent.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
Signed-off-by: Radim Krčmář <rkrcmar@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Radim Krčmář 2018-02-01 22:16:21 +01:00 • committed by Paolo Bonzini
parent f75e4924f0
commit fe2a3027e7
5 changed files with 13 additions and 6 deletions
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8
arch/x86/kernel/kvm.c
View file

@ -341,10 +341,10 @@ static void kvm_guest_cpu_init(void)
#endif
pa |= KVM_ASYNC_PF_ENABLED;
/* Async page fault support for L1 hypervisor is optional */
if (wrmsr_safe(MSR_KVM_ASYNC_PF_EN,
(pa | KVM_ASYNC_PF_DELIVERY_AS_PF_VMEXIT) & 0xffffffff, pa >> 32) < 0)
wrmsrl(MSR_KVM_ASYNC_PF_EN, pa);
if (kvm_para_has_feature(KVM_FEATURE_ASYNC_PF_VMEXIT))
pa |= KVM_ASYNC_PF_DELIVERY_AS_PF_VMEXIT;
wrmsrl(MSR_KVM_ASYNC_PF_EN, pa);
__this_cpu_write(apf_reason.enabled, 1);
printk(KERN_INFO"KVM setup async PF for cpu %d\n",
smp_processor_id());