kvm/x86: rework guest entry logic

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>