linux-kernel - [PATCH 10/43] KVM: VMX: Move init_vmcs() invocation to vmx_vcpu

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Date:   Fri, 23 Apr 2021 17:46:12 -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 10/43] KVM: VMX: Move init_vmcs() invocation to vmx_vcpu_reset()

Initialize constant VMCS state in vcpu_vcpu_reset() instead of in
vmx_vcpu_create(), which allows for the removal of the open coded "vCPU
load" sequence since ->vcpu_reset() is invoked while the vCPU is properly
loaded (which is the entire point of vCPU reset...).

Deferring 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.

Signed-off-by: Sean Christopherson <seanjc@...gle.com>
---
 arch/x86/kvm/vmx/vmx.c | 16 +++++-----------
 1 file changed, 5 insertions(+), 11 deletions(-)

diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index e90952ca6087..856aa44b17d5 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -4396,10 +4396,6 @@ static void vmx_compute_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)
@@ -4498,6 +4494,9 @@ static void vmx_vcpu_reset(struct kvm_vcpu *vcpu, bool init_event)
 	u32 eax, dummy;
 	u64 cr0;
 
+	if (!init_event)
+		init_vmcs(vmx);
+
 	vmx->rmode.vm86_active = 0;
 	vmx->spec_ctrl = 0;
 
@@ -6905,7 +6904,7 @@ static void vmx_free_vcpu(struct kvm_vcpu *vcpu)
 static int vmx_create_vcpu(struct kvm_vcpu *vcpu)
 {
 	struct vcpu_vmx *vmx;
-	int i, cpu, err;
+	int i, err;
 
 	BUILD_BUG_ON(offsetof(struct vcpu_vmx, vcpu) != 0);
 	vmx = to_vmx(vcpu);
@@ -6991,12 +6990,7 @@ static int vmx_create_vcpu(struct kvm_vcpu *vcpu)
 	vmx->msr_bitmap_mode = 0;
 
 	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)
-- 
2.31.1.498.g6c1eba8ee3d-goog