linux-kernel - [PATCH v2 04/10] KVM: x86: Remove defunct setting of CR0.ET for guests during vCPU create

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:   Mon, 20 Sep 2021 17:02:57 -0700
From:   Sean Christopherson <seanjc@...gle.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     Sean Christopherson <seanjc@...gle.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, Reiji Watanabe <reijiw@...gle.com>
Subject: [PATCH v2 04/10] KVM: x86: Remove defunct setting of CR0.ET for
 guests during vCPU create

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.

Signed-off-by: Sean Christopherson <seanjc@...gle.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)
-- 
2.33.0.464.g1972c5931b-goog