[Xen-devel] [3.16.y-ckt stable] Patch "x86/cpu: Fix SMAP check in PVOPS environments" has been added to staging queue

[Luis Henriques <luis.henriques@xxxxxxxxxxxxx>]

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

    x86/cpu: Fix SMAP check in PVOPS environments

to the linux-3.16.y-queue branch of the 3.16.y-ckt extended stable tree 
which can be found at:

    http://kernel.ubuntu.com/git/ubuntu/linux.git/log/?h=linux-3.16.y-queue

This patch is scheduled to be released in version 3.16.7-ckt22.

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

For more information about the 3.16.y-ckt tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Luis

------

From adcdc7daa6ad7966746e520292a473703ebf8741 Mon Sep 17 00:00:00 2001
From: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
Date: Wed, 3 Jun 2015 10:31:14 +0100
Subject: x86/cpu: Fix SMAP check in PVOPS environments

commit 581b7f158fe0383b492acd1ce3fb4e99d4e57808 upstream.

There appears to be no formal statement of what pv_irq_ops.save_fl() is
supposed to return precisely.  Native returns the full flags, while lguest and
Xen only return the Interrupt Flag, and both have comments by the
implementations stating that only the Interrupt Flag is looked at.  This may
have been true when initially implemented, but no longer is.

To make matters worse, the Xen PVOP leaves the upper bits undefined, making
the BUG_ON() undefined behaviour.  Experimentally, this now trips for 32bit PV
guests on Broadwell hardware.  The BUG_ON() is consistent for an individual
build, but not consistent for all builds.  It has also been a sitting timebomb
since SMAP support was introduced.

Use native_save_fl() instead, which will obtain an accurate view of the AC
flag.

Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
Reviewed-by: David Vrabel <david.vrabel@xxxxxxxxxx>
Tested-by: Rusty Russell <rusty@xxxxxxxxxxxxxxx>
Cc: Rusty Russell <rusty@xxxxxxxxxxxxxxx>
Cc: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
Cc: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
Cc: <lguest@xxxxxxxxxxxxxxxx>
Cc: Xen-devel <xen-devel@xxxxxxxxxxxxx>
Link: 
http://lkml.kernel.org/r/1433323874-6927-1-git-send-email-andrew.cooper3@xxxxxxxxxx
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Signed-off-by: Luis Henriques <luis.henriques@xxxxxxxxxxxxx>
---
 arch/x86/kernel/cpu/common.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
index 8fc57acf86f4..3b12b4d1a560 100644
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -282,10 +282,9 @@ __setup("nosmap", setup_disable_smap);

 static __always_inline void setup_smap(struct cpuinfo_x86 *c)
 {
-       unsigned long eflags;
+       unsigned long eflags = native_save_fl();

        /* This should have been cleared long ago */
-       raw_local_save_flags(eflags);
        BUG_ON(eflags & X86_EFLAGS_AC);

        if (cpu_has(c, X86_FEATURE_SMAP)) {

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