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[91.219.240.2]) by smtp.gmail.com with ESMTPSA id b23sm5028357wmd.37.2020.07.14.07.11.51 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 14 Jul 2020 07:11:52 -0700 (PDT) From: Vitaly Kuznetsov To: Sean Christopherson Cc: Wanpeng Li , Jim Mattson , Joerg Roedel , kvm@vger.kernel.org, linux-kernel@vger.kernel.org, Oliver Upton , Peter Shier , Paolo Bonzini Subject: Re: [PATCH] KVM: x86: Don't attempt to load PDPTRs when 64-bit mode is enabled In-Reply-To: <20200714132120.GA14404@linux.intel.com> References: <20200714015732.32426-1-sean.j.christopherson@intel.com> <87wo36s3wb.fsf@vitty.brq.redhat.com> <20200714132120.GA14404@linux.intel.com> Date: Tue, 14 Jul 2020 16:11:50 +0200 Message-ID: <87tuyarxsp.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: > On Tue, Jul 14, 2020 at 02:00:04PM +0200, Vitaly Kuznetsov wrote: >> Sean Christopherson writes: >> > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c >> > index 95ef629228691..5f526d94c33f3 100644 >> > --- a/arch/x86/kvm/x86.c >> > +++ b/arch/x86/kvm/x86.c >> > @@ -819,22 +819,22 @@ int kvm_set_cr0(struct kvm_vcpu *vcpu, unsigned long cr0) >> > if ((cr0 & X86_CR0_PG) && !(cr0 & X86_CR0_PE)) >> > return 1; >> > >> > - if (cr0 & X86_CR0_PG) { >> > #ifdef CONFIG_X86_64 >> > - if (!is_paging(vcpu) && (vcpu->arch.efer & EFER_LME)) { >> > - int cs_db, cs_l; >> > + if ((vcpu->arch.efer & EFER_LME) && !is_paging(vcpu) && >> > + (cr0 & X86_CR0_PG)) { >> >> it seems we have more than one occurance of "if (vcpu->arch.efer & >> EFER_LME)" under "#ifdef CONFIG_X86_64" and we alredy have >> >> static inline int is_long_mode(struct kvm_vcpu *vcpu) >> { >> #ifdef CONFIG_X86_64 >> return vcpu->arch.efer & EFER_LMA; >> #else >> return 0; >> #endif >> } >> >> so if we use this instead, the compilers will just throw away the >> non-reachable blocks when !(#ifdef CONFIG_X86_64), right? > > EFER.LME vs. EFER.LMA. The kvm_set_cr0() check is specifically looking at > the case where EFER.LME=1, EFER.LMA=0, and CR0.PG is being toggled on, i.e. > long mode is being enabled. EFER_LMA won't be set until vmx_set_cr0() does > enter_lmode(). Oops, shame on me :-( Would it make sense to introduce something like is_long_mode() (e.g. is_efer_lme()) for LME and #ifdef CONFIG_X86_64? I see the same checks in vmx_set_cr0()/svm_set_cr0())? -- Vitaly