From: Vitaly Kuznetsov <vkuznets@redhat.com>
To: Sean Christopherson <sean.j.christopherson@intel.com>
Cc: Wanpeng Li <wanpengli@tencent.com>,
Jim Mattson <jmattson@google.com>, Joerg Roedel <joro@8bytes.org>,
kvm@vger.kernel.org, linux-kernel@vger.kernel.org,
Oliver Upton <oupton@google.com>, Peter Shier <pshier@google.com>,
Paolo Bonzini <pbonzini@redhat.com>
Subject: Re: [PATCH] KVM: x86: Don't attempt to load PDPTRs when 64-bit mode is enabled
Date: Tue, 14 Jul 2020 16:11:50 +0200 [thread overview]
Message-ID: <87tuyarxsp.fsf@vitty.brq.redhat.com> (raw)
In-Reply-To: <20200714132120.GA14404@linux.intel.com>
Sean Christopherson <sean.j.christopherson@intel.com> writes:
> On Tue, Jul 14, 2020 at 02:00:04PM +0200, Vitaly Kuznetsov wrote:
>> Sean Christopherson <sean.j.christopherson@intel.com> 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
next prev parent reply other threads:[~2020-07-14 14:12 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-07-14 1:57 [PATCH] KVM: x86: Don't attempt to load PDPTRs when 64-bit mode is enabled Sean Christopherson
2020-07-14 12:00 ` Vitaly Kuznetsov
2020-07-14 13:21 ` Sean Christopherson
2020-07-14 14:11 ` Vitaly Kuznetsov [this message]
2020-07-14 18:55 ` Jim Mattson
2020-07-14 18:58 ` Sean Christopherson
2020-07-14 19:02 ` Jim Mattson
2020-08-04 18:41 ` Sean Christopherson
2020-08-04 18:46 ` Jim Mattson
2020-08-04 19:09 ` Sean Christopherson
2020-08-05 7:04 ` Maxim Levitsky
2020-08-06 21:32 ` Jim Mattson
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