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([2001:b07:6468:f312:5e2c:eb9a:a8b6:fd3e]) by smtp.googlemail.com with ESMTPSA id j7-20020a05600c1c0700b0037c2c6d2a91sm3927627wms.2.2022.03.01.09.57.08 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 01 Mar 2022 09:57:09 -0800 (PST) Message-ID: <13c4ac55-5b08-bdd9-5cfd-71e68c672825@redhat.com> Date: Tue, 1 Mar 2022 18:57:07 +0100 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.5.0 Subject: Re: [PATCH] x86: kvm Require const tsc for RT Content-Language: en-US To: Sebastian Andrzej Siewior , kvm@vger.kernel.org, x86@kernel.org Cc: Borislav Petkov , Dave Hansen , "H. Peter Anvin" , Ingo Molnar , Jim Mattson , Joerg Roedel , Sean Christopherson , Thomas Gleixner , Vitaly Kuznetsov , Wanpeng Li References: From: Paolo Bonzini In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org On 3/1/22 18:55, Sebastian Andrzej Siewior wrote: > From: Thomas Gleixner > Date: Sun, 6 Nov 2011 12:26:18 +0100 > > Non constant TSC is a nightmare on bare metal already, but with > virtualization it becomes a complete disaster because the workarounds > are horrible latency wise. That's also a preliminary for running RT in > a guest on top of a RT host. > > Signed-off-by: Thomas Gleixner > Signed-off-by: Sebastian Andrzej Siewior > --- > arch/x86/kvm/x86.c | 6 ++++++ > 1 file changed, 6 insertions(+) > > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c > index 82a9dcd8c67fe..54d2090d04e7a 100644 > --- a/arch/x86/kvm/x86.c > +++ b/arch/x86/kvm/x86.c > @@ -8826,6 +8826,12 @@ int kvm_arch_init(void *opaque) > goto out; > } > > + if (IS_ENABLED(CONFIG_PREEMPT_RT) && !boot_cpu_has(X86_FEATURE_CONSTANT_TSC)) { > + pr_err("RT requires X86_FEATURE_CONSTANT_TSC\n"); > + r = -EOPNOTSUPP; > + goto out; > + } > + > r = -ENOMEM; > > x86_emulator_cache = kvm_alloc_emulator_cache(); Acked-by: Paolo Bonzini Thanks, Paolo