linux-kernel - [PATCH 2/3] KVM: VMX: Move RESET emulation to vmx_vcpu

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Date:   Tue, 14 Sep 2021 16:08:39 -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 2/3] KVM: VMX: Move RESET emulation to vmx_vcpu_reset()

Move vCPU RESET emulation, including initializating of select VMCS state,
to vmx_vcpu_reset().  Drop the open coded "vCPU load" sequence, as
->vcpu_reset() is invoked while the vCPU is properly loaded (which is
kind of the point of ->vcpu_reset()...).  Hopefully KVM will someday
expose a dedicated RESET ioctl(), and in the meantime separating "create"
from "RESET" is a nice cleanup.

Deferring VMCS initialization is effectively a nop as it's impossible to
safely access the VMCS between the current call site and its new home, as
both the vCPU and the pCPU are put immediately after init_vmcs(), i.e.
the VMCS isn't guaranteed to be loaded.

Note, task preemption is not a problem as vmx_sched_in() _can't_ touch
the VMCS as ->sched_in() is invoked before the vCPU, and thus VMCS, is
reloaded.  I.e. the preemption path also can't consume VMCS state.

Cc: Reiji Watanabe <reijiw@...gle.com>
Signed-off-by: Sean Christopherson <seanjc@...gle.com>
---
 arch/x86/kvm/vmx/vmx.c | 61 +++++++++++++++++++++---------------------
 1 file changed, 31 insertions(+), 30 deletions(-)

diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index dc274b4c9912..629427cf8f4e 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -4327,10 +4327,6 @@ static u32 vmx_secondary_exec_control(struct vcpu_vmx *vmx)
 
 #define VMX_XSS_EXIT_BITMAP 0
 
-/*
- * Noting that the initialization of Guest-state Area of VMCS is in
- * vmx_vcpu_reset().
- */
 static void init_vmcs(struct vcpu_vmx *vmx)
 {
 	if (nested)
@@ -4435,10 +4431,39 @@ static void init_vmcs(struct vcpu_vmx *vmx)
 	vmx_setup_uret_msrs(vmx);
 }
 
+static void __vmx_vcpu_reset(struct kvm_vcpu *vcpu)
+{
+	struct vcpu_vmx *vmx = to_vmx(vcpu);
+
+	init_vmcs(vmx);
+
+	if (nested)
+		memcpy(&vmx->nested.msrs, &vmcs_config.nested, sizeof(vmx->nested.msrs));
+
+	vcpu_setup_sgx_lepubkeyhash(vcpu);
+
+	vmx->nested.posted_intr_nv = -1;
+	vmx->nested.current_vmptr = -1ull;
+	vmx->nested.hv_evmcs_vmptr = EVMPTR_INVALID;
+
+	vcpu->arch.microcode_version = 0x100000000ULL;
+	vmx->msr_ia32_feature_control_valid_bits = FEAT_CTL_LOCKED;
+
+	/*
+	 * Enforce invariant: pi_desc.nv is always either POSTED_INTR_VECTOR
+	 * or POSTED_INTR_WAKEUP_VECTOR.
+	 */
+	vmx->pi_desc.nv = POSTED_INTR_VECTOR;
+	vmx->pi_desc.sn = 1;
+}
+
 static void vmx_vcpu_reset(struct kvm_vcpu *vcpu, bool init_event)
 {
 	struct vcpu_vmx *vmx = to_vmx(vcpu);
 
+	if (!init_event)
+		__vmx_vcpu_reset(vcpu);
+
 	vmx->rmode.vm86_active = 0;
 	vmx->spec_ctrl = 0;
 
@@ -6797,7 +6822,7 @@ static int vmx_create_vcpu(struct kvm_vcpu *vcpu)
 {
 	struct vmx_uret_msr *tsx_ctrl;
 	struct vcpu_vmx *vmx;
-	int i, cpu, err;
+	int i, err;
 
 	BUILD_BUG_ON(offsetof(struct vcpu_vmx, vcpu) != 0);
 	vmx = to_vmx(vcpu);
@@ -6856,12 +6881,7 @@ static int vmx_create_vcpu(struct kvm_vcpu *vcpu)
 	}
 
 	vmx->loaded_vmcs = &vmx->vmcs01;
-	cpu = get_cpu();
-	vmx_vcpu_load(vcpu, cpu);
-	vcpu->cpu = cpu;
-	init_vmcs(vmx);
-	vmx_vcpu_put(vcpu);
-	put_cpu();
+
 	if (cpu_need_virtualize_apic_accesses(vcpu)) {
 		err = alloc_apic_access_page(vcpu->kvm);
 		if (err)
@@ -6874,25 +6894,6 @@ static int vmx_create_vcpu(struct kvm_vcpu *vcpu)
 			goto free_vmcs;
 	}
 
-	if (nested)
-		memcpy(&vmx->nested.msrs, &vmcs_config.nested, sizeof(vmx->nested.msrs));
-
-	vcpu_setup_sgx_lepubkeyhash(vcpu);
-
-	vmx->nested.posted_intr_nv = -1;
-	vmx->nested.current_vmptr = -1ull;
-	vmx->nested.hv_evmcs_vmptr = EVMPTR_INVALID;
-
-	vcpu->arch.microcode_version = 0x100000000ULL;
-	vmx->msr_ia32_feature_control_valid_bits = FEAT_CTL_LOCKED;
-
-	/*
-	 * Enforce invariant: pi_desc.nv is always either POSTED_INTR_VECTOR
-	 * or POSTED_INTR_WAKEUP_VECTOR.
-	 */
-	vmx->pi_desc.nv = POSTED_INTR_VECTOR;
-	vmx->pi_desc.sn = 1;
-
 	return 0;
 
 free_vmcs:
-- 
2.33.0.309.g3052b89438-goog