linux-kernel - [PATCH 5.8 445/464] parisc: Do not use an ordered store in pa_tlb

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Date:   Mon, 17 Aug 2020 17:16:38 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, John David Anglin <dave.anglin@...l.net>,
        Helge Deller <deller@....de>
Subject: [PATCH 5.8 445/464] parisc: Do not use an ordered store in pa_tlb_lock()

From: John David Anglin <dave.anglin@...l.net>

commit e72b23dec1da5e62a0090c5da1d926778284e230 upstream.

No need to use an ordered store in pa_tlb_lock() and update the comment
regarng usage of the sid register to unlocak a spinlock in
tlb_unlock0().

Signed-off-by: John David Anglin <dave.anglin@...l.net>
Signed-off-by: Helge Deller <deller@....de>
Cc: <stable@...r.kernel.org> # v5.0+
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 arch/parisc/kernel/entry.S |    9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

--- a/arch/parisc/kernel/entry.S
+++ b/arch/parisc/kernel/entry.S
@@ -455,7 +455,7 @@
 	LDREG		0(\ptp),\pte
 	bb,<,n		\pte,_PAGE_PRESENT_BIT,3f
 	b		\fault
-	stw,ma		\spc,0(\tmp)
+	stw		\spc,0(\tmp)
 99:	ALTERNATIVE(98b, 99b, ALT_COND_NO_SMP, INSN_NOP)
 #endif
 2:	LDREG		0(\ptp),\pte
@@ -463,7 +463,12 @@
 3:
 	.endm
 
-	/* Release pa_tlb_lock lock without reloading lock address. */
+	/* Release pa_tlb_lock lock without reloading lock address.
+	   Note that the values in the register spc are limited to
+	   NR_SPACE_IDS (262144). Thus, the stw instruction always
+	   stores a nonzero value even when register spc is 64 bits.
+	   We use an ordered store to ensure all prior accesses are
+	   performed prior to releasing the lock. */
 	.macro		tlb_unlock0	spc,tmp
 #ifdef CONFIG_SMP
 98:	or,COND(=)	%r0,\spc,%r0