On 01/02/2018 12:50, Radim Krčmář wrote:
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.
Guests at least expect that KVM_ASYNC_PF_DELIVERY_AS_PF_VMEXIT might not be present when booting, so we allow userspace to handle migration compatibility by adding a KVM CPUID flag that determines the presence of KVM_ASYNC_PF_DELIVERY_AS_PF_VMEXIT.
Fixes: 52a5c155cf79 ("KVM: async_pf: Let guest support delivery of async_pf from guest mode") Cc: stable@vger.kernel.org Signed-off-by: Radim Krčmář rkrcmar@redhat.com
This has to be documented in Documentation/virtual/kvm/cpuid.txt.
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index 4c3103f449a3..c16740a06f0c 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -2139,8 +2139,10 @@ static int kvm_pv_enable_async_pf(struct kvm_vcpu *vcpu, u64 data) { gpa_t gpa = data & ~0x3f;
- /* Bits 3:5 are reserved, Should be zero */
- if (data & 0x38)
- /* Bits 3:5 are reserved, Should be zero. */
- if (data & 0x38 ||
(data & KVM_ASYNC_PF_DELIVERY_AS_PF_VMEXIT &&!guest_kvm_cpuid_has(vcpu, KVM_FEATURE_ASYNC_PF_VMEXIT)))vcpu->arch.apf.msr_val = data;
This check will break migration if the source guest and host both have the recent kernels which support KVM_ASYNC_PF_DELIVERY_AS_PF_VMEXIT, so I am not sure about it. Otherwise, the patch is okay!
Thanks,
Paolo