linux-kernel - [PATCH 27/43] KVM: VMX: Skip emulation required checks during pmode/rmode transitions

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Date:   Fri, 23 Apr 2021 17:46:29 -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
Subject: [PATCH 27/43] KVM: VMX: Skip emulation required checks during
 pmode/rmode transitions

Don't refresh "emulation required" when stuffing segments during
transitions to/from real mode when running without unrestricted guest.
The checks are unnecessary as vmx_set_cr0() unconditionally rechecks
"emulation required".  They also happen to be broken, as enter_pmode()
and enter_rmode() run with a stale vcpu->arch.cr0.

Signed-off-by: Sean Christopherson <seanjc@...gle.com>
---
 arch/x86/kvm/vmx/vmx.c | 18 ++++++++++++------
 1 file changed, 12 insertions(+), 6 deletions(-)

diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index 5f30181fd240..37bfa20a04dd 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -2827,6 +2827,8 @@ static __init int alloc_kvm_area(void)
 	return 0;
 }
 
+static void __vmx_set_segment(struct kvm_vcpu *vcpu, struct kvm_segment *var, int seg);
+
 static void fix_pmode_seg(struct kvm_vcpu *vcpu, int seg,
 		struct kvm_segment *save)
 {
@@ -2843,7 +2845,7 @@ static void fix_pmode_seg(struct kvm_vcpu *vcpu, int seg,
 		save->dpl = save->selector & SEGMENT_RPL_MASK;
 		save->s = 1;
 	}
-	vmx_set_segment(vcpu, save, seg);
+	__vmx_set_segment(vcpu, save, seg);
 }
 
 static void enter_pmode(struct kvm_vcpu *vcpu)
@@ -2864,7 +2866,7 @@ static void enter_pmode(struct kvm_vcpu *vcpu)
 
 	vmx->rmode.vm86_active = 0;
 
-	vmx_set_segment(vcpu, &vmx->rmode.segs[VCPU_SREG_TR], VCPU_SREG_TR);
+	__vmx_set_segment(vcpu, &vmx->rmode.segs[VCPU_SREG_TR], VCPU_SREG_TR);
 
 	flags = vmcs_readl(GUEST_RFLAGS);
 	flags &= RMODE_GUEST_OWNED_EFLAGS_BITS;
@@ -3399,7 +3401,7 @@ static u32 vmx_segment_access_rights(struct kvm_segment *var)
 	return ar;
 }
 
-void vmx_set_segment(struct kvm_vcpu *vcpu, struct kvm_segment *var, int seg)
+static void __vmx_set_segment(struct kvm_vcpu *vcpu, struct kvm_segment *var, int seg)
 {
 	struct vcpu_vmx *vmx = to_vmx(vcpu);
 	const struct kvm_vmx_segment_field *sf = &kvm_vmx_segment_fields[seg];
@@ -3412,7 +3414,7 @@ void vmx_set_segment(struct kvm_vcpu *vcpu, struct kvm_segment *var, int seg)
 			vmcs_write16(sf->selector, var->selector);
 		else if (var->s)
 			fix_rmode_seg(seg, &vmx->rmode.segs[seg]);
-		goto out;
+		return;
 	}
 
 	vmcs_writel(sf->base, var->base);
@@ -3434,9 +3436,13 @@ void vmx_set_segment(struct kvm_vcpu *vcpu, struct kvm_segment *var, int seg)
 		var->type |= 0x1; /* Accessed */
 
 	vmcs_write32(sf->ar_bytes, vmx_segment_access_rights(var));
+}
 
-out:
-	vmx->emulation_required = emulation_required(vcpu);
+void vmx_set_segment(struct kvm_vcpu *vcpu, struct kvm_segment *var, int seg)
+{
+	__vmx_set_segment(vcpu, var, seg);
+
+	to_vmx(vcpu)->emulation_required = emulation_required(vcpu);
 }
 
 static void vmx_get_cs_db_l_bits(struct kvm_vcpu *vcpu, int *db, int *l)
-- 
2.31.1.498.g6c1eba8ee3d-goog