[RFC PATCH kernel 1/2] perf/x86/amd: Add amd_prevent_hostibs_window() to set per-cpu ibs_flags

[Manali Shukla]

Add a function to set per-cpu ibs_flags based on an active or inactive
PreventHostIBS window.

MSR_AMD64_IBSFETCHCTL[IbsFetchEn] and MSR_AMD64_IBSOPCTL[IbsOpEn] bits
need to be cleared for PreventHostIBS feature to be enabled before VMRUN
is executed.

ENABLE bit and VALID bit for MSR_AMD64_IBSFETCHCTL are contained in the
same MSR and same is the case with MSR_AMD64_IBSOPCTL.

Consider the following scenario:
- The IBS MSR which has ENABLE bit set and VALID bit clear is read.
- During the process of clearing the ENABLE bit and writing the IBS MSR
  to disable IBS, an IBS event can occur that sets the VALID bit.
- The write operation on IBS MSR can clear the newly set VALID bit.
- Since this situation is occurring in the CLGI/STGI window
  (PreventHostIBS window), the actual NMI is not taken.
- Once VMRUN is issued, it will exit with VMEXIT_NMI. As soon as STGI is
  executed, the pending NMI will trigger.
- The IBS NMI handler checks for the VALID bit to determine if the NMI
  is generated because of IBS.
- Since VALID bit is now clear, it doesn't recognize that an IBS event
  is occurred. Due to this reason, the dazed and confused unknown NMI
  messages are generated.

amd_prevent_hostibs_window() is added to avoid these messages when
PreventHostIBS window is active and PreventHostIBS feature is enabled
for the guest.

Signed-off-by: Manali Shukla <manali.shukla@xxxxxxx>
---
 arch/x86/events/amd/ibs.c         | 64 +++++++++++++++++++++++++++++++
 arch/x86/include/asm/perf_event.h | 20 ++++++++++
 2 files changed, 84 insertions(+)

diff --git a/arch/x86/events/amd/ibs.c b/arch/x86/events/amd/ibs.c
index da3f5ebac4e1..e96a4c9ff4ba 100644
--- a/arch/x86/events/amd/ibs.c
+++ b/arch/x86/events/amd/ibs.c
@@ -30,7 +30,9 @@ static u32 ibs_caps;
 
 #define IBS_FETCH_CONFIG_MASK	(IBS_FETCH_RAND_EN | IBS_FETCH_MAX_CNT)
 #define IBS_OP_CONFIG_MASK	IBS_OP_MAX_CNT
+#define PREVENT_HOSTIBS_WINDOW  BIT(0)
 
+static DEFINE_PER_CPU(unsigned int, ibs_flags);
 
 /*
  * IBS states:
@@ -1035,6 +1037,18 @@ static int perf_ibs_handle_irq(struct perf_ibs *perf_ibs, struct pt_regs *iregs)
 		if (test_and_clear_bit(IBS_STOPPED, pcpu->state))
 			return 1;
 
+		/*
+		 * Catch NMIs generated in an active PreventHostIBS window:
+		 * incoming NMIs from an active PreventHostIBS window might have
+		 * the VALID bit cleared when it is supposed to be set due to
+		 * a race. The reason for the race is ENABLE and VALID bits for
+		 * MSR_AMD64_IBSFETCHCTL and MSR_AMD64_IBSOPCTL being in their
+		 * same respective MSRs.  Ignore all such NMIs and treat them as
+		 * handled.
+		 */
+		if (__this_cpu_read(ibs_flags) & PREVENT_HOSTIBS_WINDOW)
+			return 1;
+
 		return 0;
 	}
 
@@ -1540,3 +1554,53 @@ static __init int amd_ibs_init(void)
 
 /* Since we need the pci subsystem to init ibs we can't do this earlier: */
 device_initcall(amd_ibs_init);
+
+void amd_prevent_hostibs_window(bool active)
+{
+	if (active)
+		__this_cpu_write(ibs_flags,
+				 __this_cpu_read(ibs_flags) |
+				 PREVENT_HOSTIBS_WINDOW);
+	else
+		__this_cpu_write(ibs_flags,
+				 __this_cpu_read(ibs_flags) &
+				 ~PREVENT_HOSTIBS_WINDOW);
+}
+EXPORT_SYMBOL_GPL(amd_prevent_hostibs_window);
+
+bool amd_disable_ibs_fetch(u64 *ibs_fetch_ctl)
+{
+	*ibs_fetch_ctl = __rdmsr(MSR_AMD64_IBSFETCHCTL);
+	if (!(*ibs_fetch_ctl & IBS_FETCH_ENABLE))
+		return false;
+
+	native_wrmsrl(MSR_AMD64_IBSFETCHCTL,
+		      *ibs_fetch_ctl & ~IBS_FETCH_ENABLE);
+
+	return true;
+}
+EXPORT_SYMBOL(amd_disable_ibs_fetch);
+
+bool amd_disable_ibs_op(u64 *ibs_op_ctl)
+{
+	*ibs_op_ctl = __rdmsr(MSR_AMD64_IBSOPCTL);
+	if (!(*ibs_op_ctl & IBS_OP_ENABLE))
+		return false;
+
+	native_wrmsrl(MSR_AMD64_IBSOPCTL, *ibs_op_ctl & ~IBS_OP_ENABLE);
+
+	return true;
+}
+EXPORT_SYMBOL(amd_disable_ibs_op);
+
+void amd_restore_ibs_fetch(u64 ibs_fetch_ctl)
+{
+	native_wrmsrl(MSR_AMD64_IBSFETCHCTL, ibs_fetch_ctl);
+}
+EXPORT_SYMBOL(amd_restore_ibs_fetch);
+
+void amd_restore_ibs_op(u64 ibs_op_ctl)
+{
+	native_wrmsrl(MSR_AMD64_IBSOPCTL, ibs_op_ctl);
+}
+EXPORT_SYMBOL(amd_restore_ibs_op);
diff --git a/arch/x86/include/asm/perf_event.h b/arch/x86/include/asm/perf_event.h
index 5d0f6891ae61..1005505e23b1 100644
--- a/arch/x86/include/asm/perf_event.h
+++ b/arch/x86/include/asm/perf_event.h
@@ -561,6 +561,26 @@ static inline void intel_pt_handle_vmx(int on)
 }
 #endif
 
+#if defined(CONFIG_X86_LOCAL_APIC) && defined(CONFIG_CPU_SUP_AMD)
+extern void amd_prevent_hostibs_window(bool active);
+extern bool amd_disable_ibs_fetch(u64 *ibs_fetch_ctl);
+extern bool amd_disable_ibs_op(u64 *ibs_op_ctl);
+extern void amd_restore_ibs_fetch(u64 ibs_fetch_ctl);
+extern void amd_restore_ibs_op(u64 ibs_op_ctl);
+#else
+static inline void amd_prevent_hostibs_window(bool active) {}
+static inline bool amd_disable_ibs_fetch(u64 *ibs_fetch_ctl)
+{
+	return false;
+}
+static inline bool amd_disable_ibs_op(u64 *ibs_op_ctl)
+{
+	return false;
+}
+static inline void amd_restore_ibs_fetch(u64 ibs_fetch_ctl) {}
+static inline void amd_restore_ibs_op(u64 ibs_op_ctl) {}
+#endif
+
 #if defined(CONFIG_PERF_EVENTS) && defined(CONFIG_CPU_SUP_AMD)
  extern void amd_pmu_enable_virt(void);
  extern void amd_pmu_disable_virt(void);
-- 
2.34.1