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[91.219.240.2]) by smtp.gmail.com with ESMTPSA id dm8sm1694159edb.57.2020.10.06.00.54.09 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 06 Oct 2020 00:54:09 -0700 (PDT) From: Vitaly Kuznetsov To: Sean Christopherson Cc: Tianjia Zhang , Paolo Bonzini , Wanpeng Li , Jim Mattson , Joerg Roedel , Thomas Gleixner , Ingo Molnar , Borislav Petkov , "H. Peter Anvin" , x86@kernel.org, kvm@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] KVM: x86: filter guest NX capability for cpuid2 In-Reply-To: <20201005163743.GE11938@linux.intel.com> References: <20201005145921.84848-1-tianjia.zhang@linux.alibaba.com> <87ft6s8zdg.fsf@vitty.brq.redhat.com> <20201005163743.GE11938@linux.intel.com> Date: Tue, 06 Oct 2020 09:54:08 +0200 Message-ID: <87d01v94db.fsf@vitty.brq.redhat.com> MIME-Version: 1.0 Content-Type: text/plain Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org Sean Christopherson writes: > On Mon, Oct 05, 2020 at 05:29:47PM +0200, Vitaly Kuznetsov wrote: >> Tianjia Zhang writes: >> >> > Original KVM_SET_CPUID has removed NX on non-NX hosts as it did >> > before. but KVM_SET_CPUID2 does not. The two should be consistent. >> > >> > Signed-off-by: Tianjia Zhang >> > --- >> > arch/x86/kvm/cpuid.c | 1 + >> > 1 file changed, 1 insertion(+) >> > >> > diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c >> > index 3fd6eec202d7..3e7ba2b11acb 100644 >> > --- a/arch/x86/kvm/cpuid.c >> > +++ b/arch/x86/kvm/cpuid.c >> > @@ -257,6 +257,7 @@ int kvm_vcpu_ioctl_set_cpuid2(struct kvm_vcpu *vcpu, >> > goto out; >> > } >> > >> > + cpuid_fix_nx_cap(vcpu); >> > kvm_update_cpuid_runtime(vcpu); >> > kvm_vcpu_after_set_cpuid(vcpu); >> > out: >> >> I stumbled upon this too and came to the conclusion this is >> intentional, e.g. see this: >> >> commit 0771671749b59a507b6da4efb931c44d9691e248 >> Author: Dan Kenigsberg >> Date: Wed Nov 21 17:10:04 2007 +0200 >> >> KVM: Enhance guest cpuid management >> >> ... >> >> [avi: fix original KVM_SET_CPUID not removing nx on non-nx hosts as it did >> before] >> >> but this is a very, very old story. > > Doesn't mean it's bogus though :-) _If_ we want to extend this behavior to > KVM_SET_CPUID2, there should be a justified need. Yes, exactly. I meand to say that founding fathers of KVM left the adjustment for KVM_SET_CPUID exclusively on purpose and not by mistake :-) -- Vitaly