linux-kernel - [PATCH v2 07/46] KVM: VMX: Remove explicit MMU reset in enter

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Date:   Tue, 13 Jul 2021 09:32:45 -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 07/46] KVM: VMX: Remove explicit MMU reset in enter_rmode()

Drop an explicit MMU reset when entering emulated real mode now that the
vCPU INIT/RESET path correctly handles conditional MMU resets, e.g. if
INIT arrives while the vCPU is in 64-bit mode.

Note, while there are multiple other direct calls to vmx_set_cr0(), i.e.
paths that change CR0 without invoking kvm_post_set_cr0(), only the INIT
emulation can reach enter_rmode().  CLTS emulation only toggles CR.TS,
VM-Exit (and late VM-Fail) emulation cannot architecturally transition to
Real Mode, and VM-Enter to Real Mode is possible if and only if
Unrestricted Guest is enabled (exposed to L1).

This effectively reverts commit 8668a3c468ed ("KVM: VMX: Reset mmu
context when entering real mode")

Signed-off-by: Sean Christopherson <seanjc@...gle.com>
---
 arch/x86/kvm/vmx/vmx.c | 2 --
 1 file changed, 2 deletions(-)

diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index 825197f21700..0f5e97a904e5 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -2852,8 +2852,6 @@ static void enter_rmode(struct kvm_vcpu *vcpu)
 	fix_rmode_seg(VCPU_SREG_DS, &vmx->rmode.segs[VCPU_SREG_DS]);
 	fix_rmode_seg(VCPU_SREG_GS, &vmx->rmode.segs[VCPU_SREG_GS]);
 	fix_rmode_seg(VCPU_SREG_FS, &vmx->rmode.segs[VCPU_SREG_FS]);
-
-	kvm_mmu_reset_context(vcpu);
 }

 int vmx_set_efer(struct kvm_vcpu *vcpu, u64 efer)
-- 
2.32.0.93.g670b81a890-goog