This is a combination of ~2 series to fix bugs in the perf+KVM callbacks,
optimize the callbacks by employing static_call, and do a variety of
cleanup in both perf and KVM.

Patch 1 fixes a mostly-theoretical bug where perf can deref a NULL
pointer if KVM unregisters its callbacks while they're being accessed.
In practice, compilers tend to avoid problematic reloads of the pointer
and the PMI handler doesn't lose the race against module unloading,
i.e doesn't hit a use-after-free.

Patches 2 and 3 fix an Intel PT handling bug where KVM incorrectly
eats PT interrupts when PT is supposed to be owned entirely by the host.

Patches 4-7 clean up perf's callback infrastructure and switch to
static_call for arm64 and x86 (the only survivors).

Patches 8-13 clean up related KVM code and unify the arm64/x86 callbacks.

Based on "git://git.kernel.org/pub/scm/virt/kvm/kvm.git queue", commit
680c7e3be6a3 ("KVM: x86: Exit to userspace ...").

v2 (relatively to static_call v10)
  - Split the patch into the semantic change (multiplexed ->state) and
    introduction of static_call.
  - Don't use '0' for "not a guest RIP".
  - Handle unregister path.
  - Drop changes for architectures that can be culled entirely.

v2 (relative to v1)
  - Drop per-cpu approach. [Peter]
  - Fix mostly-theoretical reload and use-after-free with READ_ONCE(),
    WRITE_ONCE(), and synchronize_rcu(). [Peter]
  - Avoid new exports like the plague. [Peter]

v1:
  - https://lkml.kernel.org/r/20210827005718.585190-1-seanjc@google.com

v10 static_call:
  - https://lkml.kernel.org/r/20210806133802.3528-2-lingshan.zhu@intel.com

Like Xu (2):
  perf/core: Rework guest callbacks to prepare for static_call support
  perf/core: Use static_call to optimize perf_guest_info_callbacks

Sean Christopherson (11):
  perf: Ensure perf_guest_cbs aren't reloaded between !NULL check and
    deref
  KVM: x86: Register perf callbacks after calling vendor's
    hardware_setup()
  KVM: x86: Register Processor Trace interrupt hook iff PT enabled in
    guest
  perf: Stop pretending that perf can handle multiple guest callbacks
  perf: Force architectures to opt-in to guest callbacks
  KVM: x86: Drop current_vcpu for kvm_running_vcpu + kvm_arch_vcpu
    variable
  KVM: x86: More precisely identify NMI from guest when handling PMI
  KVM: Move x86's perf guest info callbacks to generic KVM
  KVM: x86: Move Intel Processor Trace interrupt handler to vmx.c
  KVM: arm64: Convert to the generic perf callbacks
  KVM: arm64: Drop perf.c and fold its tiny bits of code into arm.c /
    pmu.c

 arch/arm/kernel/perf_callchain.c   | 28 ++------------
 arch/arm64/Kconfig                 |  1 +
 arch/arm64/include/asm/kvm_host.h  | 13 ++++++-
 arch/arm64/kernel/perf_callchain.c | 28 +++++++++++---
 arch/arm64/kvm/Makefile            |  2 +-
 arch/arm64/kvm/arm.c               | 11 +++++-
 arch/arm64/kvm/perf.c              | 62 ------------------------------
 arch/arm64/kvm/pmu.c               |  8 ++++
 arch/csky/kernel/perf_callchain.c  | 10 -----
 arch/nds32/kernel/perf_event_cpu.c | 29 ++------------
 arch/riscv/kernel/perf_callchain.c | 10 -----
 arch/x86/Kconfig                   |  1 +
 arch/x86/events/core.c             | 36 ++++++++++++++---
 arch/x86/events/intel/core.c       |  7 ++--
 arch/x86/include/asm/kvm_host.h    |  8 +++-
 arch/x86/kvm/pmu.c                 |  2 +-
 arch/x86/kvm/svm/svm.c             |  2 +-
 arch/x86/kvm/vmx/vmx.c             | 25 +++++++++++-
 arch/x86/kvm/x86.c                 | 58 +++++-----------------------
 arch/x86/kvm/x86.h                 | 17 ++++++--
 arch/x86/xen/pmu.c                 | 32 +++++++--------
 include/kvm/arm_pmu.h              |  1 +
 include/linux/kvm_host.h           | 10 +++++
 include/linux/perf_event.h         | 26 ++++++++-----
 init/Kconfig                       |  3 ++
 kernel/events/core.c               | 24 ++++++------
 virt/kvm/kvm_main.c                | 40 +++++++++++++++++++
 27 files changed, 245 insertions(+), 249 deletions(-)
 delete mode 100644 arch/arm64/kvm/perf.c

-- 
2.33.0.259.gc128427fd7-goog

On Fri, Aug 27, 2021 at 05:35:45PM -0700, Sean Christopherson wrote:
> Like Xu (2):
>   perf/core: Rework guest callbacks to prepare for static_call support
>   perf/core: Use static_call to optimize perf_guest_info_callbacks
> 
> Sean Christopherson (11):
>   perf: Ensure perf_guest_cbs aren't reloaded between !NULL check and
>     deref
>   KVM: x86: Register perf callbacks after calling vendor's
>     hardware_setup()
>   KVM: x86: Register Processor Trace interrupt hook iff PT enabled in
>     guest
>   perf: Stop pretending that perf can handle multiple guest callbacks
>   perf: Force architectures to opt-in to guest callbacks
>   KVM: x86: Drop current_vcpu for kvm_running_vcpu + kvm_arch_vcpu
>     variable
>   KVM: x86: More precisely identify NMI from guest when handling PMI
>   KVM: Move x86's perf guest info callbacks to generic KVM
>   KVM: x86: Move Intel Processor Trace interrupt handler to vmx.c
>   KVM: arm64: Convert to the generic perf callbacks
>   KVM: arm64: Drop perf.c and fold its tiny bits of code into arm.c /
>     pmu.c

Lets keep the whole intel_pt crud inside x86...

---
Index: linux-2.6/arch/x86/events/core.c
===================================================================
--- linux-2.6.orig/arch/x86/events/core.c
+++ linux-2.6/arch/x86/events/core.c
@@ -92,7 +92,7 @@ DEFINE_STATIC_CALL_RET0(x86_pmu_guest_ge
 
 DEFINE_STATIC_CALL_RET0(x86_guest_state, *(perf_guest_cbs->state));
 DEFINE_STATIC_CALL_RET0(x86_guest_get_ip, *(perf_guest_cbs->get_ip));
-DEFINE_STATIC_CALL_RET0(x86_guest_handle_intel_pt_intr, *(perf_guest_cbs->handle_intel_pt_intr));
+DEFINE_STATIC_CALL_RET0(x86_guest_handle_intel_pt_intr, unsigned int (*)(void));
 
 void arch_perf_update_guest_cbs(struct perf_guest_info_callbacks *guest_cbs)
 {
@@ -103,14 +103,6 @@ void arch_perf_update_guest_cbs(struct p
 		static_call_update(x86_guest_state, (void *)&__static_call_return0);
 		static_call_update(x86_guest_get_ip, (void *)&__static_call_return0);
 	}
-
-	/* Implementing ->handle_intel_pt_intr is optional. */
-	if (guest_cbs && guest_cbs->handle_intel_pt_intr)
-		static_call_update(x86_guest_handle_intel_pt_intr,
-				   guest_cbs->handle_intel_pt_intr);
-	else
-		static_call_update(x86_guest_handle_intel_pt_intr,
-				   (void *)&__static_call_return0);
 }
 
 u64 __read_mostly hw_cache_event_ids
Index: linux-2.6/arch/x86/events/intel/core.c
===================================================================
--- linux-2.6.orig/arch/x86/events/intel/core.c
+++ linux-2.6/arch/x86/events/intel/core.c
@@ -2782,7 +2782,7 @@ static void intel_pmu_reset(void)
 	local_irq_restore(flags);
 }
 
-DECLARE_STATIC_CALL(x86_guest_handle_intel_pt_intr, *(perf_guest_cbs->handle_intel_pt_intr));
+DECLARE_STATIC_CALL(x86_guest_handle_intel_pt_intr, unsigned int (*)(void));
 
 static int handle_pmi_common(struct pt_regs *regs, u64 status)
 {
Index: linux-2.6/arch/x86/kvm/x86.c
===================================================================
--- linux-2.6.orig/arch/x86/kvm/x86.c
+++ linux-2.6/arch/x86/kvm/x86.c
@@ -10960,7 +10960,14 @@ int kvm_arch_hardware_setup(void *opaque
 	memcpy(&kvm_x86_ops, ops->runtime_ops, sizeof(kvm_x86_ops));
 	kvm_ops_static_call_update();
 
-	kvm_register_perf_callbacks(ops->handle_intel_pt_intr);
+	kvm_register_perf_callbacks();
+	if (ops->handle_intel_pt_intr) {
+		static_call_update(x86_guest_handle_intel_pt_intr,
+				   ops->handle_intel_pt_intr);
+	} else {
+		static_call_update(x86_guest_handle_intel_pt_intr,
+				   (void *)&__static_call_return0);
+	}
 
 	if (!kvm_cpu_cap_has(X86_FEATURE_XSAVES))
 		supported_xss = 0;
Index: linux-2.6/include/linux/perf_event.h
===================================================================
--- linux-2.6.orig/include/linux/perf_event.h
+++ linux-2.6/include/linux/perf_event.h
@@ -32,7 +32,6 @@
 struct perf_guest_info_callbacks {
 	unsigned int			(*state)(void);
 	unsigned long			(*get_ip)(void);
-	unsigned int			(*handle_intel_pt_intr)(void);
 };
 
 #ifdef CONFIG_HAVE_HW_BREAKPOINT
Index: linux-2.6/virt/kvm/kvm_main.c
===================================================================
--- linux-2.6.orig/virt/kvm/kvm_main.c
+++ linux-2.6/virt/kvm/kvm_main.c
@@ -5374,12 +5374,10 @@ static unsigned long kvm_guest_get_ip(vo
 static struct perf_guest_info_callbacks kvm_guest_cbs = {
 	.state			= kvm_guest_state,
 	.get_ip			= kvm_guest_get_ip,
-	.handle_intel_pt_intr	= NULL,
 };
 
-void kvm_register_perf_callbacks(unsigned int (*pt_intr_handler)(void))
+void kvm_register_perf_callbacks(void)
 {
-	kvm_guest_cbs.handle_intel_pt_intr = pt_intr_handler;
 	perf_register_guest_info_callbacks(&kvm_guest_cbs);
 }
 #endif
Index: linux-2.6/arch/arm64/kvm/arm.c
===================================================================
--- linux-2.6.orig/arch/arm64/kvm/arm.c
+++ linux-2.6/arch/arm64/kvm/arm.c
@@ -1749,7 +1749,7 @@ static int init_subsystems(void)
 		goto out;
 
 	kvm_pmu_init();
-	kvm_register_perf_callbacks(NULL);
+	kvm_register_perf_callbacks();
 
 	kvm_sys_reg_table_init();
 
Index: linux-2.6/include/linux/kvm_host.h
===================================================================
--- linux-2.6.orig/include/linux/kvm_host.h
+++ linux-2.6/include/linux/kvm_host.h
@@ -1121,7 +1121,7 @@ static inline bool kvm_arch_intc_initial
 #ifdef __KVM_WANT_PERF_CALLBACKS
 unsigned long kvm_arch_vcpu_get_ip(struct kvm_vcpu *vcpu);
 
-void kvm_register_perf_callbacks(unsigned int (*pt_intr_handler)(void));
+void kvm_register_perf_callbacks(void);
 static inline void kvm_unregister_perf_callbacks(void)
 {
 	perf_unregister_guest_info_callbacks();