[PATCH v3 0/4] KVM: x86: hyper-v: Conditionally allow SynIC with APICv/AVIC

[Vitaly Kuznetsov <vkuznets@redhat.com>]

Changes since v2:
- First two patches got merged, rebase.
- Use 'enable_apicv = avic = ...' in PATCH1 [Paolo]
- Collect R-b tags for PATCH2 [Sean, Max]
- Use hv_apicv_update_work() to get out of SRCU lock [Max]
- "KVM: x86: Check for pending interrupts when APICv is getting disabled"
  added.

Original description:

APICV_INHIBIT_REASON_HYPERV is currently unconditionally forced upon
SynIC activation as SynIC's AutoEOI is incompatible with APICv/AVIC. It is,
however, possible to track whether the feature was actually used by the
guest and only inhibit APICv/AVIC when needed.

The series can be tested with the followin hack:

diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
index 9a48f138832d..65a9974f80d9 100644
--- a/arch/x86/kvm/cpuid.c
+++ b/arch/x86/kvm/cpuid.c
@@ -147,6 +147,13 @@ void kvm_update_cpuid_runtime(struct kvm_vcpu *vcpu)
                                           vcpu->arch.ia32_misc_enable_msr &
                                           MSR_IA32_MISC_ENABLE_MWAIT);
        }
+
+       /* Dirty hack: force HV_DEPRECATING_AEOI_RECOMMENDED. Not to be merged! */
+       best = kvm_find_cpuid_entry(vcpu, HYPERV_CPUID_ENLIGHTMENT_INFO, 0);
+       if (best) {
+               best->eax &= ~HV_X64_APIC_ACCESS_RECOMMENDED;
+               best->eax |= HV_DEPRECATING_AEOI_RECOMMENDED;
+       }
 }
 EXPORT_SYMBOL_GPL(kvm_update_cpuid_runtime);
 
Vitaly Kuznetsov (4):
  KVM: x86: Use common 'enable_apicv' variable for both APICv and AVIC
  KVM: x86: Drop vendor specific functions for APICv/AVIC enablement
  KVM: x86: Check for pending interrupts when APICv is getting disabled
  KVM: x86: hyper-v: Deactivate APICv only when AutoEOI feature is in
    use

 arch/x86/include/asm/kvm_host.h |  9 +++++-
 arch/x86/kvm/hyperv.c           | 51 +++++++++++++++++++++++++++++----
 arch/x86/kvm/svm/avic.c         | 14 ++++-----
 arch/x86/kvm/svm/svm.c          | 22 ++++++++------
 arch/x86/kvm/svm/svm.h          |  2 --
 arch/x86/kvm/vmx/capabilities.h |  1 -
 arch/x86/kvm/vmx/vmx.c          |  2 --
 arch/x86/kvm/x86.c              | 18 ++++++++++--
 8 files changed, 86 insertions(+), 33 deletions(-)

-- 
2.31.1