[PATCH 2/3] KVM: VMX: Move RESET emulation to vmx_vcpu_reset()

Sean Christopherson
2021-09-14T23:09:28Z

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@google.com>
Signed-off-by: Sean Christopherson <seanjc@google.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