kvm/x86: rework guest entry logic

For consistency and clarity, migrate x86 over to the generic helpers for
guest timing and lockdep/RCU/tracing management, and remove the
x86-specific helpers.

Prior to this patch, the guest timing was entered in
kvm_guest_enter_irqoff() (called by svm_vcpu_enter_exit() and
svm_vcpu_enter_exit()), and was exited by the call to
vtime_account_guest_exit() within vcpu_enter_guest().

To minimize duplication and to more clearly balance entry and exit, both
entry and exit of guest timing are placed in vcpu_enter_guest(), using
the new guest_timing_{enter,exit}_irqoff() helpers. When context
tracking is used a small amount of additional time will be accounted
towards guests; tick-based accounting is unnaffected as IRQs are
disabled at this point and not enabled until after the return from the
guest.

This also corrects (benign) mis-balanced context tracking accounting
introduced in commits:

  ae95f566b3d22ade ("KVM: X86: TSCDEADLINE MSR emulation fastpath")
  26efe2fd92e50822 ("KVM: VMX: Handle preemption timer fastpath")

Where KVM can enter a guest multiple times, calling vtime_guest_enter()
without a corresponding call to vtime_account_guest_exit(), and with
vtime_account_system() called when vtime_account_guest() should be used.
As account_system_time() checks PF_VCPU and calls account_guest_time(),
this doesn't result in any functional problem, but is unnecessarily
confusing.

Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Acked-by: Paolo Bonzini <pbonzini@redhat.com>
Reviewed-by: Nicolas Saenz Julienne <nsaenzju@redhat.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Jim Mattson <jmattson@google.com>
Cc: Joerg Roedel <joro@8bytes.org>
Cc: Sean Christopherson <seanjc@google.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vitaly Kuznetsov <vkuznets@redhat.com>
Cc: Wanpeng Li <wanpengli@tencent.com>
Message-Id: <20220201132926.3301912-4-mark.rutland@arm.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index 5772dd6..ea2f7f3 100644 (file)
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -3630,7 +3630,7 @@ static noinstr void svm_vcpu_enter_exit(struct kvm_vcpu *vcpu)
        struct vcpu_svm *svm = to_svm(vcpu);
        unsigned long vmcb_pa = svm->current_vmcb->pa;
 
-       kvm_guest_enter_irqoff();
+       guest_state_enter_irqoff();
 
        if (sev_es_guest(vcpu->kvm)) {
                __svm_sev_es_vcpu_run(vmcb_pa);
@@ -3650,7 +3650,7 @@ static noinstr void svm_vcpu_enter_exit(struct kvm_vcpu *vcpu)
                vmload(__sme_page_pa(sd->save_area));
        }
 
-       kvm_guest_exit_irqoff();
+       guest_state_exit_irqoff();
 }
 
 static __no_kcsan fastpath_t svm_vcpu_run(struct kvm_vcpu *vcpu)

diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index 3c0ba5b..c0c256c 100644 (file)
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -6767,7 +6767,7 @@ static fastpath_t vmx_exit_handlers_fastpath(struct kvm_vcpu *vcpu)
 static noinstr void vmx_vcpu_enter_exit(struct kvm_vcpu *vcpu,
                                        struct vcpu_vmx *vmx)
 {
-       kvm_guest_enter_irqoff();
+       guest_state_enter_irqoff();
 
        /* L1D Flush includes CPU buffer clear to mitigate MDS */
        if (static_branch_unlikely(&vmx_l1d_should_flush))
@@ -6783,7 +6783,7 @@ static noinstr void vmx_vcpu_enter_exit(struct kvm_vcpu *vcpu,
 
        vcpu->arch.cr2 = native_read_cr2();
 
-       kvm_guest_exit_irqoff();
+       guest_state_exit_irqoff();
 }
 
 static fastpath_t vmx_vcpu_run(struct kvm_vcpu *vcpu)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index c25a6ef..fec3dd4 100644 (file)
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -10088,6 +10088,8 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
                set_debugreg(0, 7);
        }
 
+       guest_timing_enter_irqoff();
+
        for (;;) {
                /*
                 * Assert that vCPU vs. VM APICv state is consistent.  An APICv
@@ -10172,7 +10174,7 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
         * of accounting via context tracking, but the loss of accuracy is
         * acceptable for all known use cases.
         */
-       vtime_account_guest_exit();
+       guest_timing_exit_irqoff();
 
        if (lapic_in_kernel(vcpu)) {
                s64 delta = vcpu->arch.apic->lapic_timer.advance_expire_delta;

diff --git a/arch/x86/kvm/x86.h b/arch/x86/kvm/x86.h
index 1ebd5a7..20c7a1f 100644 (file)
--- a/arch/x86/kvm/x86.h
+++ b/arch/x86/kvm/x86.h
@@ -10,51 +10,6 @@
 
 void kvm_spurious_fault(void);
 
-static __always_inline void kvm_guest_enter_irqoff(void)
-{
-       /*
-        * VMENTER enables interrupts (host state), but the kernel state is
-        * interrupts disabled when this is invoked. Also tell RCU about
-        * it. This is the same logic as for exit_to_user_mode().
-        *
-        * This ensures that e.g. latency analysis on the host observes
-        * guest mode as interrupt enabled.
-        *
-        * guest_enter_irqoff() informs context tracking about the
-        * transition to guest mode and if enabled adjusts RCU state
-        * accordingly.
-        */
-       instrumentation_begin();
-       trace_hardirqs_on_prepare();
-       lockdep_hardirqs_on_prepare(CALLER_ADDR0);
-       instrumentation_end();
-
-       guest_enter_irqoff();
-       lockdep_hardirqs_on(CALLER_ADDR0);
-}
-
-static __always_inline void kvm_guest_exit_irqoff(void)
-{
-       /*
-        * VMEXIT disables interrupts (host state), but tracing and lockdep
-        * have them in state 'on' as recorded before entering guest mode.
-        * Same as enter_from_user_mode().
-        *
-        * context_tracking_guest_exit() restores host context and reinstates
-        * RCU if enabled and required.
-        *
-        * This needs to be done immediately after VM-Exit, before any code
-        * that might contain tracepoints or call out to the greater world,
-        * e.g. before x86_spec_ctrl_restore_host().
-        */
-       lockdep_hardirqs_off(CALLER_ADDR0);
-       context_tracking_guest_exit();
-
-       instrumentation_begin();
-       trace_hardirqs_off_finish();
-       instrumentation_end();
-}
-
 #define KVM_NESTED_VMENTER_CONSISTENCY_CHECK(consistency_check)                \
 ({                                                                     \
        bool failed = (consistency_check);                              \