From: David Laight <David.Laight@ACULAB.COM>
To: "'Armin Wolf'" <W_Armin@gmx.de>, "'Pali Rohár'" <pali@kernel.org>,
"Guenter Roeck" <linux@roeck-us.net>
Cc: "jdelvare@suse.com" <jdelvare@suse.com>,
"linux-hwmon@vger.kernel.org" <linux-hwmon@vger.kernel.org>,
"linux-assembly@vger.kernel.org" <linux-assembly@vger.kernel.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: RE: [PATCH v4] hwmon: (dell-smm) Improve assembly code
Date: Wed, 23 Feb 2022 22:35:11 +0000 [thread overview]
Message-ID: <63a04993864f4c08923ed753d83cdf37@AcuMS.aculab.com> (raw)
In-Reply-To: <4b5ca065-06a4-c1ff-ed16-3bbb038ee6e0@gmx.de>
From: Armin Wolf
> Sent: 23 February 2022 21:39
...
> > As far as this patch goes I think I'd add a 'stc' (set carry)
> > instruction before the first 'outb'.
> > Then if the 'something magic happens here' doesn't happen (because
> > you aren't on the right kind of motherboard) the action fails.
> >
> > David
>
> We already check for such scenarios by checking if eax changed.
> I would not set the carry flag before doing a SMM call since im
> not sure if the firmware code always clears the carry flag when
> the call was successful.
> If for example the firmware code only sets the carry flag on
> error and otherwise ignores the carry flag, we might create some
> false negatives when a successful SMM call leaves the carry flag set.
If you are worried about that you should be clearing carry on entry.
David
-
Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
Registration No: 1397386 (Wales)
next prev parent reply other threads:[~2022-02-23 22:35 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-02-20 19:08 [PATCH v4] hwmon: (dell-smm) Improve assembly code Armin Wolf
2022-02-22 16:54 ` Guenter Roeck
2022-02-22 17:51 ` Pali Rohár
2022-02-22 19:46 ` David Laight
2022-02-23 21:39 ` Armin Wolf
2022-02-23 22:35 ` David Laight [this message]
2022-02-24 0:45 ` Guenter Roeck
2022-03-02 18:07 ` Guenter Roeck
2022-06-20 15:21 ` Guenter Roeck
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