From: Vitaly Kuznetsov <vkuznets@redhat.com>
To: Sean Christopherson <seanjc@google.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>,
Wanpeng Li <wanpengli@tencent.com>,
Jim Mattson <jmattson@google.com>, Joerg Roedel <joro@8bytes.org>,
kvm@vger.kernel.org, linux-kernel@vger.kernel.org,
Reiji Watanabe <reijiw@google.com>
Subject: Re: [PATCH v2 04/10] KVM: x86: Remove defunct setting of CR0.ET for guests during vCPU create
Date: Tue, 21 Sep 2021 16:23:30 +0200 [thread overview]
Message-ID: <87zgs680t9.fsf@vitty.brq.redhat.com> (raw)
In-Reply-To: <20210921000303.400537-5-seanjc@google.com>
Sean Christopherson <seanjc@google.com> writes:
> Drop code to set CR0.ET for the guest during initialization of the guest
> FPU. The code was added as a misguided bug fix by commit 380102c8e431
> ("KVM Set the ET flag in CR0 after initializing FX") to resolve an issue
> where vcpu->cr0 (now vcpu->arch.cr0) was not correctly initialized on SVM
> systems. While init_vmcb() did set CR0.ET, it only did so in the VMCB,
> and subtly did not update vcpu->cr0. Stuffing CR0.ET worked around the
> immediate problem, but did not fix the real bug of vcpu->cr0 and the VMCB
> being out of sync. That underlying bug was eventually remedied by commit
> 18fa000ae453 ("KVM: SVM: Reset cr0 properly on vcpu reset").
>
> No functional change intended.
fx_init() is only called from kvm_arch_vcpu_create() (and inlined later
in the series) a few lines before kvm_vcpu_reset() which stuffs CR0 with
X86_CR0_ET too and it doesn't seem that arch.cr0 value is important in
between.
>
> Signed-off-by: Sean Christopherson <seanjc@google.com>
> ---
> arch/x86/kvm/x86.c | 2 --
> 1 file changed, 2 deletions(-)
>
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index ab907a0b9eeb..e0bff5473813 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -10628,8 +10628,6 @@ static void fx_init(struct kvm_vcpu *vcpu)
> * Ensure guest xcr0 is valid for loading
> */
> vcpu->arch.xcr0 = XFEATURE_MASK_FP;
> -
> - vcpu->arch.cr0 |= X86_CR0_ET;
> }
>
> void kvm_free_guest_fpu(struct kvm_vcpu *vcpu)
Reviewed-by: Vitaly Kuznetsov <vkuznets@redhat.com>
--
Vitaly
next prev parent reply other threads:[~2021-09-21 14:23 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-09-21 0:02 [PATCH v2 00/10] KVM: x86: Clean up RESET "emulation" Sean Christopherson
2021-09-21 0:02 ` [PATCH v2 01/10] KVM: x86: Mark all registers as avail/dirty at vCPU creation Sean Christopherson
2021-09-21 13:40 ` Vitaly Kuznetsov
2021-09-21 0:02 ` [PATCH v2 02/10] KVM: x86: Clear KVM's cached guest CR3 at RESET/INIT Sean Christopherson
2021-09-21 13:52 ` Vitaly Kuznetsov
2021-09-21 13:55 ` Vitaly Kuznetsov
2021-09-21 17:35 ` Paolo Bonzini
2021-09-21 0:02 ` [PATCH v2 03/10] KVM: x86: Do not mark all registers as avail/dirty during RESET/INIT Sean Christopherson
2021-09-21 0:02 ` [PATCH v2 04/10] KVM: x86: Remove defunct setting of CR0.ET for guests during vCPU create Sean Christopherson
2021-09-21 14:23 ` Vitaly Kuznetsov [this message]
2021-09-21 0:02 ` [PATCH v2 05/10] KVM: x86: Remove defunct setting of XCR0 for guest " Sean Christopherson
2021-09-21 14:37 ` Vitaly Kuznetsov
2021-09-21 0:02 ` [PATCH v2 06/10] KVM: x86: Fold fx_init() into kvm_arch_vcpu_create() Sean Christopherson
2021-09-21 14:52 ` Vitaly Kuznetsov
2021-10-06 23:04 ` Sean Christopherson
2021-09-21 0:03 ` [PATCH v2 07/10] KVM: VMX: Drop explicit zeroing of MSR guest values at vCPU creation Sean Christopherson
2021-09-21 15:02 ` Vitaly Kuznetsov
2021-09-21 0:03 ` [PATCH v2 08/10] KVM: VMX: Move RESET emulation to vmx_vcpu_reset() Sean Christopherson
2021-09-21 0:03 ` [PATCH v2 09/10] KVM: SVM: Move RESET emulation to svm_vcpu_reset() Sean Christopherson
2021-09-21 0:03 ` [PATCH v2 10/10] KVM: x86: WARN on non-zero CRs at RESET to detect improper initalization Sean Christopherson
2021-09-21 13:59 ` Vitaly Kuznetsov
2021-09-23 16:23 ` [PATCH v2 00/10] KVM: x86: Clean up RESET "emulation" Paolo Bonzini
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