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[91.219.240.2]) by smtp.gmail.com with ESMTPSA id b67sm1206714wmc.38.2020.02.24.14.25.25 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 24 Feb 2020 14:25:25 -0800 (PST) From: Vitaly Kuznetsov To: Sean Christopherson Cc: Paolo Bonzini , Wanpeng Li , Jim Mattson , Joerg Roedel , kvm@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 46/61] KVM: x86: Remove the unnecessary loop on CPUID 0x7 sub-leafs In-Reply-To: <20200201185218.24473-47-sean.j.christopherson@intel.com> References: <20200201185218.24473-1-sean.j.christopherson@intel.com> <20200201185218.24473-47-sean.j.christopherson@intel.com> Date: Mon, 24 Feb 2020 23:25:24 +0100 Message-ID: <87tv3fmxm3.fsf@vitty.brq.redhat.com> MIME-Version: 1.0 Content-Type: text/plain Sender: kvm-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org Sean Christopherson writes: > Explicitly handle CPUID 0x7 sub-leaf 1. The kernel is currently aware > of exactly one feature in CPUID 0x7.1, which means there is room for > another 127 features before CPUID 0x7.2 will see the light of day, i.e. > the looping is likely to be dead code for years to come. > > Signed-off-by: Sean Christopherson > --- > arch/x86/kvm/cpuid.c | 8 +++----- > 1 file changed, 3 insertions(+), 5 deletions(-) > > diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c > index 7362e5238799..47f61f4497fb 100644 > --- a/arch/x86/kvm/cpuid.c > +++ b/arch/x86/kvm/cpuid.c > @@ -533,11 +533,9 @@ static inline int __do_cpuid_func(struct kvm_cpuid_array *array, u32 function) > if (boot_cpu_has(X86_FEATURE_AMD_SSBD)) > cpuid_entry_set(entry, X86_FEATURE_SPEC_CTRL_SSBD); > > - for (i = 1, max_idx = entry->eax; i <= max_idx; i++) { > - if (WARN_ON_ONCE(i > 1)) > - break; > - > - entry = do_host_cpuid(array, function, i); > + /* KVM only supports 0x7.0 and 0x7.1, capped above via min(). */ > + if (entry->eax == 1) { > + entry = do_host_cpuid(array, function, 1); > if (!entry) > goto out; Reviewed-by: Vitaly Kuznetsov -- Vitaly