linux-kernel - RE: [PATCH 03/32] ACPICA: Hardware: Enable 64-bit firmware waking vector for selected FACS.

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Date:	Wed, 24 Jun 2015 00:15:33 +0000
From:	"Zheng, Lv" <lv.zheng@...el.com>
To:	"Rafael J. Wysocki" <rjw@...ysocki.net>
CC:	"Wysocki, Rafael J" <rafael.j.wysocki@...el.com>,
	"Brown, Len" <len.brown@...el.com>, Lv Zheng <zetalog@...il.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-acpi@...r.kernel.org" <linux-acpi@...r.kernel.org>,
	"Moore, Robert" <robert.moore@...el.com>
Subject: RE: [PATCH 03/32] ACPICA: Hardware: Enable 64-bit firmware waking
 vector for selected FACS.

Hi, Rafael

> From: Rafael J. Wysocki [mailto:rjw@...ysocki.net]
> Sent: Wednesday, June 24, 2015 8:30 AM
> 
> On Friday, June 19, 2015 11:38:28 AM Lv Zheng wrote:
> > ACPICA commit 7aa598d711644ab0de5f70ad88f1e2de253115e4
> >
> > The root cause of the reported bug might be one of the followings:
> > 1. BIOS may favor the 64-bit firmware waking vector address when the
> >    version of the FACS is greater than 0 and Linux currently only supports
> >    resuming from the real mode, so the 64-bit firmware waking vector has
> >    never been set and might be invalid to BIOS while the commit enables
> >    higher version FACS.
> > 2. BIOS may favor the FACS reported via the "FIRMWARE_CTRL" field in the
> >    FADT while the commit doesn't set the firmware waking vector address of
> >    the FACS reported by "FIRMWARE_CTRL", it only sets the firware waking
> >    vector address of the FACS reported by "X_FIRMWARE_CTRL".
> >
> > This patch excludes the cases that can trigger the bugs caused by the root
> > cause 1.
> >
> > ACPI specification says:
> > A. 32-bit FACS address (FIRMWARE_CTRL field in FADT):
> >    Physical memory address of the FACS, where OSPM and firmware exchange
> >    control information.
> >    If the X_FIRMWARE_CTRL field contains a non zero value then this field
> >    must be zero.
> >    A zero value indicates that no FACS is specified by this field.
> > B. 64-bit FACS address (X_FIRMWARE_CTRL field in FADT):
> >    64bit physical memory address of the FACS.
> >    This field is used when the physical address of the FACS is above 4GB.
> >    If the FIRMWARE_CTRL field contains a non zero value then this field
> >    must be zero.
> >    A zero value indicates that no FACS is specified by this field.
> > Thus the 32bit and 64bit firmware waking vector should indicate completely
> > different resuming environment - real mode (1MB addressable) and non real
> > mode (4GB+ addressable) and currently Linux only supports resuming from
> > real mode.
> >
> > This patch enables 64-bit firmware waking vector for selected FACS via
> > acpi_set_firmware_waking_vector() so that it's up to OSPMs to determine which
> > resuming mode should be used by BIOS and ACPICA changes won't trigger the
> > bugs caused by the root cause 1. For example, Linux can pass
> > physical_address64=0 as the parameter of acpi_set_firmware_waking_vector() to
> > indicate no 64bit waking vector support. Lv Zheng.
> >
> > Link: https://bugzilla.kernel.org/show_bug.cgi?id=74021
> > Link: https://github.com/acpica/acpica/commit/7aa598d7
> > Reported-and-tested-by: Oswald Buddenhagen <ossi@....org>
> > Signed-off-by: Lv Zheng <lv.zheng@...el.com>
> > Signed-off-by: Bob Moore <robert.moore@...el.com>
> 
> So what the patch does is to replace two functions, acpi_set_firmware_waking_vector()
> taking one u32 argument and acpi_set_firmware_waking_vector64() taking one u64
> argument, with a modified acpi_set_firmware_waking_vector() taking two arguments
> of type acpi_physical_address.  And it breaks compliation when applied to Linux
> as is AFAICS, doesn't it?

Yes, and the fix is patch 04/32.

> I guess the point is to allow the OS to set firmware_waking_vector *and* clear
> xfirmware_waking_vector at the same time (by passing 0 as the second argument
> of the function).  And that helps to address the issue when xfirmware_waking_vector
> has a random value to start with, we don't clear it and the BIOS thinks it is OK
> to use it, right?

Yes.

> If that's the case, this patch should be combined with [4/32] and the signal-to-noise
> ratio of [4/32] needs to be increased quite a bit.

I'll combine the 2 patches.

Thanks and best regards
-Lv