linux-kernel - [PATCH RESENT v4] dell_rbu: make firmware payload memory uncachable

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Message-Id: <20180418054634.10289-1-tiwai@suse.de>
Date:   Wed, 18 Apr 2018 07:46:34 +0200
From:   Takashi Iwai <tiwai@...e.de>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     Stuart Hayes <stuart.w.hayes@...il.com>,
        linux-kernel@...r.kernel.org
Subject: [PATCH RESENT v4] dell_rbu: make firmware payload memory uncachable

From: Stuart Hayes <stuart.w.hayes@...il.com>

The dell_rbu driver takes firmware update payloads and puts them in memory so
the system BIOS can find them after a reboot.  This sometimes fails (though
rarely), because the memory containing the payload is in the CPU cache but
never gets written back to main memory before the system is rebooted (CPU
cache contents are lost on reboot).

With this patch, the payload memory will be changed to uncachable to ensure
that the payload is actually in main memory before the system is rebooted.

Signed-off-by: Stuart Hayes <stuart.w.hayes@...il.com>
Reviewed-by: Takashi Iwai <tiwai@...e.de>
Signed-off-by: Takashi Iwai <tiwai@...e.de>
---
v2 Added include, removed extra parentheses
v3 Corrected formatting and include line
v4 Moved set_memory_uc() outside the while loop so that the memory is
   definitely allocated before it is set to uncachable

Andrew, could you pick up this orphan one?  Thanks!

diff --git a/drivers/firmware/dell_rbu.c b/drivers/firmware/dell_rbu.c
index 2f452f1f7c8a..53f27a6e2d76 100644
--- a/drivers/firmware/dell_rbu.c
+++ b/drivers/firmware/dell_rbu.c
@@ -45,6 +45,7 @@
 #include <linux/moduleparam.h>
 #include <linux/firmware.h>
 #include <linux/dma-mapping.h>
+#include <asm/set_memory.h>
 
 MODULE_AUTHOR("Abhay Salunke <abhay_salunke@...l.com>");
 MODULE_DESCRIPTION("Driver for updating BIOS image on DELL systems");
@@ -181,6 +182,11 @@ static int create_packet(void *data, size_t length)
 			packet_data_temp_buf = NULL;
 		}
 	}
+	/*
+	 * set to uncachable or it may never get written back before reboot
+	 */
+	set_memory_uc((unsigned long)packet_data_temp_buf, 1 << ordernum);
+
 	spin_lock(&rbu_data.lock);
 
 	newpacket->data = packet_data_temp_buf;
@@ -349,6 +355,8 @@ static void packet_empty_list(void)
 		 * to make sure there are no stale RBU packets left in memory
 		 */
 		memset(newpacket->data, 0, rbu_data.packetsize);
+		set_memory_wb((unsigned long)newpacket->data,
+			1 << newpacket->ordernum);
 		free_pages((unsigned long) newpacket->data,
 			newpacket->ordernum);
 		kfree(newpacket);