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authorAndrew Cooper <andrew.cooper3@citrix.com>2015-06-03 10:31:14 +0100
committerSasha Levin <alexander.levin@verizon.com>2016-10-22 16:38:10 -0400
commitbb2f5ed8935a47f78a70ac48e58e993de46430e0 (patch)
parente45a502bdeae5a075257c4f061d1ff4ff0821354 (diff)
x86/cpu: Fix SMAP check in PVOPS environments
[ Upstream commit 581b7f158fe0383b492acd1ce3fb4e99d4e57808 ] 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@citrix.com> Reviewed-by: David Vrabel <david.vrabel@citrix.com> Tested-by: Rusty Russell <rusty@rustcorp.com.au> Cc: Rusty Russell <rusty@rustcorp.com.au> Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com> Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com> Cc: <lguest@lists.ozlabs.org> Cc: Xen-devel <xen-devel@lists.xen.org> CC: stable@vger.kernel.org Link: http://lkml.kernel.org/r/1433323874-6927-1-git-send-email-andrew.cooper3@citrix.com Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Signed-off-by: Sasha Levin <alexander.levin@verizon.com>
1 files changed, 1 insertions, 2 deletions
diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
index 88635b301694..69608a4f554b 100644
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -291,10 +291,9 @@ __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)) {