From:   Jon Doron <arilou@gmail.com>
To:     kvm@vger.kernel.org
Cc:     vkuznets@redhat.com, pbonzini@redhat.com, rvkagan@yandex-team.ru,
        Jon Doron <arilou@gmail.com>
Subject: [PATCH v1 1/1] x86/kvm/hyper-v: Synic default SCONTROL MSR needs to be enabled
Date:   Fri, 17 Jul 2020 15:52:38 +0300
Message-Id: <20200717125238.1103096-2-arilou@gmail.com>
In-Reply-To: <20200717125238.1103096-1-arilou@gmail.com>
References: <20200717125238.1103096-1-arilou@gmail.com>
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Based on an analysis of the HyperV firmwares (Gen1 and Gen2) it seems
like the SCONTROL is not being set to the ENABLED state as like we have
thought.

Also from a test done by Vitaly Kuznetsov, running a nested HyperV it
was concluded that the first access to the SCONTROL MSR with a read
resulted with the value of 0x1, aka HV_SYNIC_CONTROL_ENABLE.

It's important to note that this diverges from the value states in the
HyperV TLFS of 0.

Signed-off-by: Jon Doron <arilou@gmail.com>
---
 arch/x86/kvm/hyperv.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/arch/x86/kvm/hyperv.c b/arch/x86/kvm/hyperv.c
index af9cdb426dd2..814d3aee5cef 100644
--- a/arch/x86/kvm/hyperv.c
+++ b/arch/x86/kvm/hyperv.c
@@ -900,6 +900,7 @@ int kvm_hv_activate_synic(struct kvm_vcpu *vcpu, bool dont_zero_synic_pages)
 	kvm_request_apicv_update(vcpu->kvm, false, APICV_INHIBIT_REASON_HYPERV);
 	synic->active = true;
 	synic->dont_zero_synic_pages = dont_zero_synic_pages;
+	synic->control = HV_SYNIC_CONTROL_ENABLE;
 	return 0;
 }
 
-- 
2.24.1