linux-kernel - Re: [PATCH 4.19 383/422] firmware: dell

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Message-ID: <20191120132845.GA32699@duo.ucw.cz>
Date:   Wed, 20 Nov 2019 14:28:46 +0100
From:   Pavel Machek <pavel@...x.de>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        Stuart Hayes <stuart.w.hayes@...il.com>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Sasha Levin <sashal@...nel.org>
Subject: Re: [PATCH 4.19 383/422] firmware: dell_rbu: Make payload memory
 uncachable

Hi!

> From: Stuart Hayes <stuart.w.hayes@...il.com>
> 
> [ Upstream commit 6aecee6ad41cf97c0270f72da032c10eef025bf0 ]
> 
> 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.

Flushing the cache sounds like easier way to accomplish same
goal... and perhaps with better performance too.

Best regards,
								Pavel
								
> +++ 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);
> -- 
> 2.20.1
> 
> 

-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html

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