linux-kernel - [PATCH v2 4/7] KVM: x86: hyper-v: always advertise HV_STIMER_DIRECT_MODE

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Date:   Thu, 24 Sep 2020 16:57:54 +0200
From:   Vitaly Kuznetsov <vkuznets@...hat.com>
To:     kvm@...r.kernel.org, Paolo Bonzini <pbonzini@...hat.com>
Cc:     Sean Christopherson <sean.j.christopherson@...el.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Eduardo Habkost <ehabkost@...hat.com>,
        Jon Doron <arilou@...il.com>, linux-kernel@...r.kernel.org
Subject: [PATCH v2 4/7] KVM: x86: hyper-v: always advertise HV_STIMER_DIRECT_MODE_AVAILABLE

HV_STIMER_DIRECT_MODE_AVAILABLE is the last conditionally set feature bit
in KVM_GET_SUPPORTED_HV_CPUID but it doesn't have to be conditional: first,
this bit is only an indication to userspace VMM that direct mode stimers
are supported, it still requires manual enablement (enabling SynIC) to
work so no VMM should just blindly copy it to guest CPUIDs. Second,
lapic_in_kernel() is a must for SynIC. Expose the bit unconditionally.

Signed-off-by: Vitaly Kuznetsov <vkuznets@...hat.com>
---
 arch/x86/kvm/hyperv.c | 8 +-------
 1 file changed, 1 insertion(+), 7 deletions(-)

diff --git a/arch/x86/kvm/hyperv.c b/arch/x86/kvm/hyperv.c
index 6da20f91cd59..503829f71270 100644
--- a/arch/x86/kvm/hyperv.c
+++ b/arch/x86/kvm/hyperv.c
@@ -2028,13 +2028,7 @@ int kvm_vcpu_ioctl_get_hv_cpuid(struct kvm_vcpu *vcpu, struct kvm_cpuid2 *cpuid,
 			ent->ebx |= HV_DEBUGGING;
 			ent->edx |= HV_X64_GUEST_DEBUGGING_AVAILABLE;
 			ent->edx |= HV_FEATURE_DEBUG_MSRS_AVAILABLE;
-
-			/*
-			 * Direct Synthetic timers only make sense with in-kernel
-			 * LAPIC
-			 */
-			if (lapic_in_kernel(vcpu))
-				ent->edx |= HV_STIMER_DIRECT_MODE_AVAILABLE;
+			ent->edx |= HV_STIMER_DIRECT_MODE_AVAILABLE;
 
 			break;
 
-- 
2.25.4