linux-kernel - [PATCH 3.12 113/127] sparc64: Handle extremely large kernel TSB range flushes sanely.

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Message-Id: <72c18e0a4691e69c781c9d6e1dda6b1748adbcb6.1480062521.git.jslaby@suse.cz>
Date:   Fri, 25 Nov 2016 09:30:26 +0100
From:   Jiri Slaby <jslaby@...e.cz>
To:     stable@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org,
        "David S. Miller" <davem@...emloft.net>,
        Jiri Slaby <jslaby@...e.cz>
Subject: [PATCH 3.12 113/127] sparc64: Handle extremely large kernel TSB range flushes sanely.

From: "David S. Miller" <davem@...emloft.net>

3.12-stable review patch.  If anyone has any objections, please let me know.

===============

[ Upstream commit 849c498766060a16aad5b0e0d03206726e7d2fa4 ]

If the number of pages we are flushing is more than twice the number
of entries in the TSB, just scan the TSB table for matches rather
than probing each and every page in the range.

Based upon a patch and report by James Clarke.

Signed-off-by: David S. Miller <davem@...emloft.net>
Signed-off-by: Jiri Slaby <jslaby@...e.cz>
---
 arch/sparc/mm/tsb.c | 17 +++++++++++++++++
 1 file changed, 17 insertions(+)

diff --git a/arch/sparc/mm/tsb.c b/arch/sparc/mm/tsb.c
index 12f172117043..48a09e48d444 100644
--- a/arch/sparc/mm/tsb.c
+++ b/arch/sparc/mm/tsb.c
@@ -26,6 +26,20 @@ static inline int tag_compare(unsigned long tag, unsigned long vaddr)
 	return (tag == (vaddr >> 22));
 }
 
+static void flush_tsb_kernel_range_scan(unsigned long start, unsigned long end)
+{
+	unsigned long idx;
+
+	for (idx = 0; idx < KERNEL_TSB_NENTRIES; idx++) {
+		struct tsb *ent = &swapper_tsb[idx];
+		unsigned long match = idx << 13;
+
+		match |= (ent->tag << 22);
+		if (match >= start && match < end)
+			ent->tag = (1UL << TSB_TAG_INVALID_BIT);
+	}
+}
+
 /* TSB flushes need only occur on the processor initiating the address
  * space modification, not on each cpu the address space has run on.
  * Only the TLB flush needs that treatment.
@@ -35,6 +49,9 @@ void flush_tsb_kernel_range(unsigned long start, unsigned long end)
 {
 	unsigned long v;
 
+	if ((end - start) >> PAGE_SHIFT >= 2 * KERNEL_TSB_NENTRIES)
+		return flush_tsb_kernel_range_scan(start, end);
+
 	for (v = start; v < end; v += PAGE_SIZE) {
 		unsigned long hash = tsb_hash(v, PAGE_SHIFT,
 					      KERNEL_TSB_NENTRIES);
-- 
2.10.2