| From 581b7f158fe0383b492acd1ce3fb4e99d4e57808 Mon Sep 17 00:00:00 2001 |
| From: Andrew Cooper <andrew.cooper3@citrix.com> |
| Date: Wed, 3 Jun 2015 10:31:14 +0100 |
| Subject: x86/cpu: Fix SMAP check in PVOPS environments |
| |
| From: Andrew Cooper <andrew.cooper3@citrix.com> |
| |
| 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@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> |
| 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: Greg Kroah-Hartman <gregkh@linuxfoundation.org> |
| |
| --- |
| arch/x86/kernel/cpu/common.c | 3 +-- |
| 1 file changed, 1 insertion(+), 2 deletions(-) |
| |
| --- a/arch/x86/kernel/cpu/common.c |
| +++ b/arch/x86/kernel/cpu/common.c |
| @@ -280,10 +280,9 @@ __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)) { |