Hi Greg, please apply the attched backported patch to the 4.9 stable tree. It is needed to boot Xen PV guests (broken since commit c43b4ff972a986c85bdd8dc1aa05fe23b29ef99c which I didn't realize due to my kernel parameters when testing). Juergen
>From cc2872574d060fb3d35fd28c81327ee887f540ef Mon Sep 17 00:00:00 2001 From: Juergen Gross <jgross@xxxxxxxx> Date: Thu, 5 Jul 2018 12:29:48 +0200 Subject: [PATCH-for-4.9-stable] x86/cpu: Re-apply forced caps every time CPU caps are re-read Calling get_cpu_cap() will reset a bunch of CPU features. This will cause the system to lose track of force-set and force-cleared features in the words that are reset until the end of CPU initialization. This can cause X86_FEATURE_FPU, for example, to change back and forth during boot and potentially confuse CPU setup. To minimize the chance of confusion, re-apply forced caps every time get_cpu_cap() is called. Signed-off-by: Andy Lutomirski <luto@xxxxxxxxxx> Reviewed-by: Borislav Petkov <bp@xxxxxxx> Cc: Borislav Petkov <bp@xxxxxxxxx> Cc: Brian Gerst <brgerst@xxxxxxxxx> Cc: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx> Cc: Fenghua Yu <fenghua.yu@xxxxxxxxx> Cc: H. Peter Anvin <hpa@xxxxxxxxx> Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> Cc: Matthew Whitehead <tedheadster@xxxxxxxxx> Cc: Oleg Nesterov <oleg@xxxxxxxxxx> Cc: One Thousand Gnomes <gnomes@xxxxxxxxxxxxxxxxxxx> Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx> Cc: Rik van Riel <riel@xxxxxxxxxx> Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx> Cc: Yu-cheng Yu <yu-cheng.yu@xxxxxxxxx> Link: http://lkml.kernel.org/r/c817eb373d2c67c2c81413a70fc9b845fa34a37e.1484705016.git.luto@xxxxxxxxxx Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx> Signed-off-by: Juergen Gross <jgross@xxxxxxxx> --- upstream commit: 60d3450167433f2d099ce2869dc52dd9e7dc9b29 needed for Xen PV guests to boot, was broken since commit c43b4ff972a986c85bdd8dc1aa05fe23b29ef99c --- arch/x86/kernel/cpu/common.c | 7 +++++++ 1 file changed, 7 insertions(+) diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c index b0fd028b2eee..7a4279d8a902 100644 --- a/arch/x86/kernel/cpu/common.c +++ b/arch/x86/kernel/cpu/common.c @@ -848,6 +848,13 @@ void get_cpu_cap(struct cpuinfo_x86 *c) init_scattered_cpuid_features(c); init_speculation_control(c); + + /* + * Clear/Set all flags overridden by options, after probe. + * This needs to happen each time we re-probe, which may happen + * several times during CPU initialization. + */ + apply_forced_caps(c); } static void identify_cpu_without_cpuid(struct cpuinfo_x86 *c) -- 2.13.7
