[3.13.y.z extended stable] Patch "x86/intel/quark: Switch off CR4.PGE so TLB flush uses CR3 instead" 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/intel/quark: Switch off CR4.PGE so TLB flush uses CR3 instead

to the linux-3.13.y-queue branch of the 3.13.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-3.13.y-queue

This patch is scheduled to be released in version 3.13.11.10.

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

For more information about the 3.13.y.z tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Kamal

------

>From 47d0fffc8bb40fcda84218444dcb1b4dfc8a7b24 Mon Sep 17 00:00:00 2001
From: Bryan O'Donoghue <pure.logic at nexus-software.ie>
Date: Wed, 24 Sep 2014 00:26:24 +0100
Subject: x86/intel/quark: Switch off CR4.PGE so TLB flush uses CR3 instead

commit ee1b5b165c0a2f04d2107e634e51f05d0eb107de upstream.

Quark x1000 advertises PGE via the standard CPUID method
PGE bits exist in Quark X1000's PTEs. In order to flush
an individual PTE it is necessary to reload CR3 irrespective
of the PTE.PGE bit.

See Quark Core_DevMan_001.pdf section 6.4.11

This bug was fixed in Galileo kernels, unfixed vanilla kernels are expected to
crash and burn on this platform.

Signed-off-by: Bryan O'Donoghue <pure.logic at nexus-software.ie>
Cc: Borislav Petkov <bp at alien8.de>
Link: http://lkml.kernel.org/r/1411514784-14885-1-git-send-email-pure.logic@nexus-software.ie
Signed-off-by: Ingo Molnar <mingo at kernel.org>
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
---
 arch/x86/kernel/cpu/intel.c | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/arch/x86/kernel/cpu/intel.c b/arch/x86/kernel/cpu/intel.c
index bbe1b8b..46d612d 100644
--- a/arch/x86/kernel/cpu/intel.c
+++ b/arch/x86/kernel/cpu/intel.c
@@ -154,6 +154,21 @@ static void early_init_intel(struct cpuinfo_x86 *c)
 			setup_clear_cpu_cap(X86_FEATURE_ERMS);
 		}
 	}
+
+	/*
+	 * Intel Quark Core DevMan_001.pdf section 6.4.11
+	 * "The operating system also is required to invalidate (i.e., flush)
+	 *  the TLB when any changes are made to any of the page table entries.
+	 *  The operating system must reload CR3 to cause the TLB to be flushed"
+	 *
+	 * As a result cpu_has_pge() in arch/x86/include/asm/tlbflush.h should
+	 * be false so that __flush_tlb_all() causes CR3 insted of CR4.PGE
+	 * to be modified
+	 */
+	if (c->x86 == 5 && c->x86_model == 9) {
+		pr_info("Disabling PGE capability bit\n");
+		setup_clear_cpu_cap(X86_FEATURE_PGE);
+	}
 }

 #ifdef CONFIG_X86_32
--
1.9.1