Messages in this thread | | | Date | Tue, 17 Nov 2015 14:59:24 +0000 | From | Andrew Cooper <> | Subject | Re: [PATCH] x86/cpu: Fix SMAP check in PVOPS environments |
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Ping?
None of the discussion on this thread altered the contents of this patch, and the bug is still present.
~Andrew
On 03/06/15 10:31, Andrew Cooper wrote: > 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: Thomas Gleixner <tglx@linutronix.de> > CC: Ingo Molnar <mingo@redhat.com> > CC: H. Peter Anvin <hpa@zytor.com> > CC: x86@kernel.org > CC: linux-kernel@vger.kernel.org > CC: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com> > CC: Boris Ostrovsky <boris.ostrovsky@oracle.com> > CC: xen-devel <xen-devel@lists.xen.org> > CC: lguest@lists.ozlabs.org > CC: stable@vger.kernel.org > --- > 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 a62cf04..4f2fded 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)) {
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