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[91.219.240.2]) by smtp.gmail.com with ESMTPSA id u2sm17535810wrd.40.2020.05.04.08.55.11 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 04 May 2020 08:55:11 -0700 (PDT) From: Vitaly Kuznetsov To: Roman Kagan , Jon Doron Cc: kvm@vger.kernel.org, linux-hyperv@vger.kernel.org Subject: Re: [PATCH v2 0/1] x86/kvm/hyper-v: Add support to SYNIC exit on EOM In-Reply-To: <20200503191900.GA389956@rvkaganb> References: <20200416083847.1776387-1-arilou@gmail.com> <20200416120040.GA3745197@rvkaganb> <20200416125430.GL7606@jondnuc> <20200417104251.GA3009@rvkaganb> <20200418064127.GB1917435@jondnuc> <20200424133742.GA2439920@rvkaganb> <20200425061637.GF1917435@jondnuc> <20200503191900.GA389956@rvkaganb> Date: Mon, 04 May 2020 17:55:10 +0200 Message-ID: <87a72nelup.fsf@vitty.brq.redhat.com> MIME-Version: 1.0 Content-Type: text/plain Sender: linux-hyperv-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-hyperv@vger.kernel.org Roman Kagan writes: > On Sat, Apr 25, 2020 at 09:16:37AM +0300, Jon Doron wrote: > >> If that's indeed the case then probably the only thing needs fixing in my >> scenario is in QEMU where it should not really care for the SCONTROL if it's >> enabled or not. > > Right. However, even this shouldn't be necessary as SeaBIOS from that > branch would enable SCONTROL and leave it that way when passing the > control over to the bootloader, so, unless something explicitly clears > SCONTROL, it should remain set thereafter. I'd rather try going ahead > with that scheme first, because making QEMU ignore SCONTROL appears to > violate the spec. FWIW, I just checked 'genuine' Hyper-V 2016 with diff --git a/arch/x86/hyperv/hv_init.c b/arch/x86/hyperv/hv_init.c index fd51bac11b46..c5ea759728d9 100644 --- a/arch/x86/hyperv/hv_init.c +++ b/arch/x86/hyperv/hv_init.c @@ -314,10 +314,14 @@ void __init hyperv_init(void) u64 guest_id, required_msrs; union hv_x64_msr_hypercall_contents hypercall_msr; int cpuhp, i; + u64 val; if (x86_hyper_type != X86_HYPER_MS_HYPERV) return; + hv_get_synic_state(val); + printk("Hyper-V: SCONTROL state: %llx\n", val); + /* Absolutely required MSRs */ required_msrs = HV_X64_MSR_HYPERCALL_AVAILABLE | HV_X64_MSR_VP_INDEX_AVAILABLE; and it seems the default state of HV_X64_MSR_SCONTROL is '1', we should probably do the same. Is there any reason to *not* do this in KVM when KVM_CAP_HYPERV_SYNIC[,2] is enabled? -- Vitaly