[ 3.8.y.z extended stable ] Patch "x86, suspend: Handle CPUs which fail to #GP on RDMSR" has been added to staging queue

[Kamal Mostafa]

This is a note to let you know that I have just added a patch titled

    x86, suspend: Handle CPUs which fail to #GP on RDMSR

to the linux-3.8.y-queue branch of the 3.8.y.z extended stable tree 
which can be found at:

 http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.8.y-queue

This patch is scheduled to be released in version 3.8.13.6.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.8.y.z tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Kamal

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>From b6c2a3b9babff6559cb243ade2f810ff4b06344d Mon Sep 17 00:00:00 2001
From: "H. Peter Anvin" <hpa at linux.intel.com>
Date: Fri, 12 Jul 2013 16:48:12 -0700
Subject: x86, suspend: Handle CPUs which fail to #GP on RDMSR
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

commit 5ff560fd48d5b3d82fa0c3aff625c9da1a301911 upstream.

There are CPUs which have errata causing RDMSR of a nonexistent MSR to
not fault.  We would then try to WRMSR to restore the value of that
MSR, causing a crash.  Specifically, some Pentium M variants would
have this problem trying to save and restore the non-existent EFER,
causing a crash on resume.

Work around this by making sure we can write back the result at
suspend time.

Huge thanks to Christian Sünkenberg for finding the offending erratum
that finally deciphered the mystery.

Reported-and-tested-by: Johan Heinrich <onny at project-insanity.org>
Debugged-by: Christian Sünkenberg <christian.suenkenberg at student.kit.edu>
Acked-by: Rafael J. Wysocki <rjw at sisk.pl>
Link: http://lkml.kernel.org/r/51DDC972.3010005@student.kit.edu
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
---
 arch/x86/kernel/acpi/sleep.c | 18 ++++++++++++++++--
 1 file changed, 16 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kernel/acpi/sleep.c b/arch/x86/kernel/acpi/sleep.c
index d5e0d71..753dfaa 100644
--- a/arch/x86/kernel/acpi/sleep.c
+++ b/arch/x86/kernel/acpi/sleep.c
@@ -48,9 +48,20 @@ int acpi_suspend_lowlevel(void)
 #ifndef CONFIG_64BIT
 	store_gdt((struct desc_ptr *)&header->pmode_gdt);

+	/*
+	 * We have to check that we can write back the value, and not
+	 * just read it.  At least on 90 nm Pentium M (Family 6, Model
+	 * 13), reading an invalid MSR is not guaranteed to trap, see
+	 * Erratum X4 in "Intel Pentium M Processor on 90 nm Process
+	 * with 2-MB L2 Cache and Intel® Processor A100 and A110 on 90
+	 * nm process with 512-KB L2 Cache Specification Update".
+	 */
 	if (!rdmsr_safe(MSR_EFER,
 			&header->pmode_efer_low,
-			&header->pmode_efer_high))
+			&header->pmode_efer_high) &&
+	    !wrmsr_safe(MSR_EFER,
+			header->pmode_efer_low,
+			header->pmode_efer_high))
 		header->pmode_behavior |= (1 << WAKEUP_BEHAVIOR_RESTORE_EFER);
 #endif /* !CONFIG_64BIT */

@@ -61,7 +72,10 @@ int acpi_suspend_lowlevel(void)
 	}
 	if (!rdmsr_safe(MSR_IA32_MISC_ENABLE,
 			&header->pmode_misc_en_low,
-			&header->pmode_misc_en_high))
+			&header->pmode_misc_en_high) &&
+	    !wrmsr_safe(MSR_IA32_MISC_ENABLE,
+			header->pmode_misc_en_low,
+			header->pmode_misc_en_high))
 		header->pmode_behavior |=
 			(1 << WAKEUP_BEHAVIOR_RESTORE_MISC_ENABLE);
 	header->realmode_flags = acpi_realmode_flags;
--
1.8.1.2