[PATCH 2/2] powerpc/mm: Workaround Nest MMU bug with TLB invalidations

[Balbir Singh]

From: Benjamin Herrenschmidt <benh at kernel.crashing.org>

On POWER9 the Nest MMU may fail to invalidate some
translations when doing a tlbie "by PID" or "by LPID"
that is targeted at the TLB only and not the page walk
cache.

This works around it by forcing such invalidations to
escalate to RIC=2 (full invalidation of TLB *and* PWC)
when a coprocessor is in use for the context.

Signed-off-by: Benjamin Herrenschmidt <benh at kernel.crashing.org>
Signed-off-by: Balbir Singh <bsingharora at gmail.com>
[fixed a spelling and coding style to quiesce checkpatch.pl]
Tested-by: Balbir Singh <bsingharora at gmail.com>
---
 arch/powerpc/mm/tlb-radix.c | 50 ++++++++++++++++++++++++++++++++++++++-------
 1 file changed, 43 insertions(+), 7 deletions(-)

diff --git a/arch/powerpc/mm/tlb-radix.c b/arch/powerpc/mm/tlb-radix.c
index 71d1b19ad1c0..8e4c6cb4a808 100644
--- a/arch/powerpc/mm/tlb-radix.c
+++ b/arch/powerpc/mm/tlb-radix.c
@@ -151,7 +151,23 @@ static inline void _tlbiel_pid(unsigned long pid, unsigned long ric)
 static inline void _tlbie_pid(unsigned long pid, unsigned long ric)
 {
 	asm volatile("ptesync": : :"memory");
-	__tlbie_pid(pid, ric);
+
+	/*
+	 * Workaround the fact that the "ric" argument to __tlbie_pid
+	 * must be a compile-time contraint to match the "i" constraint
+	 * in the asm statement.
+	 */
+	switch (ric) {
+	case RIC_FLUSH_TLB:
+		__tlbie_pid(pid, RIC_FLUSH_TLB);
+		break;
+	case RIC_FLUSH_PWC:
+		__tlbie_pid(pid, RIC_FLUSH_PWC);
+		break;
+	case RIC_FLUSH_ALL:
+	default:
+		__tlbie_pid(pid, RIC_FLUSH_ALL);
+	}
 	asm volatile("eieio; tlbsync; ptesync": : :"memory");
 }
 
@@ -311,6 +327,16 @@ void radix__local_flush_tlb_page(struct vm_area_struct *vma, unsigned long vmadd
 }
 EXPORT_SYMBOL(radix__local_flush_tlb_page);
 
+static bool mm_needs_flush_escalation(struct mm_struct *mm)
+{
+	/*
+	 * P9 nest MMU has issues with the page walk cache
+	 * caching PTEs and not flushing them properly when
+	 * RIC = 0 for a PID/LPID invalidate
+	 */
+	return atomic_read(&mm->context.copros) != 0;
+}
+
 #ifdef CONFIG_SMP
 void radix__flush_tlb_mm(struct mm_struct *mm)
 {
@@ -321,9 +347,12 @@ void radix__flush_tlb_mm(struct mm_struct *mm)
 		return;
 
 	preempt_disable();
-	if (!mm_is_thread_local(mm))
-		_tlbie_pid(pid, RIC_FLUSH_TLB);
-	else
+	if (!mm_is_thread_local(mm)) {
+		if (mm_needs_flush_escalation(mm))
+			_tlbie_pid(pid, RIC_FLUSH_ALL);
+		else
+			_tlbie_pid(pid, RIC_FLUSH_TLB);
+	} else
 		_tlbiel_pid(pid, RIC_FLUSH_TLB);
 	preempt_enable();
 }
@@ -435,10 +464,14 @@ void radix__flush_tlb_range(struct vm_area_struct *vma, unsigned long start,
 	}
 
 	if (full) {
-		if (local)
+		if (local) {
 			_tlbiel_pid(pid, RIC_FLUSH_TLB);
-		else
-			_tlbie_pid(pid, RIC_FLUSH_TLB);
+		} else {
+			if (mm_needs_flush_escalation(mm))
+				_tlbie_pid(pid, RIC_FLUSH_ALL);
+			else
+				_tlbie_pid(pid, RIC_FLUSH_TLB);
+		}
 	} else {
 		bool hflush = false;
 		unsigned long hstart, hend;
@@ -548,6 +581,9 @@ static inline void __radix__flush_tlb_range_psize(struct mm_struct *mm,
 	}
 
 	if (full) {
+		if (!local && mm_needs_flush_escalation(mm))
+			also_pwc = true;
+
 		if (local)
 			_tlbiel_pid(pid, also_pwc ? RIC_FLUSH_ALL : RIC_FLUSH_TLB);
 		else
-- 
2.13.6