aboutsummaryrefslogtreecommitdiffstats
path: root/common/recipes-kernel/linux/linux-yocto-4.9.21/0093-x86-amd-don-t-set-X86_BUG_SYSRET_SS_ATTRS-when-runni.patch
diff options
context:
space:
mode:
Diffstat (limited to 'common/recipes-kernel/linux/linux-yocto-4.9.21/0093-x86-amd-don-t-set-X86_BUG_SYSRET_SS_ATTRS-when-runni.patch')
-rw-r--r--common/recipes-kernel/linux/linux-yocto-4.9.21/0093-x86-amd-don-t-set-X86_BUG_SYSRET_SS_ATTRS-when-runni.patch65
1 files changed, 65 insertions, 0 deletions
diff --git a/common/recipes-kernel/linux/linux-yocto-4.9.21/0093-x86-amd-don-t-set-X86_BUG_SYSRET_SS_ATTRS-when-runni.patch b/common/recipes-kernel/linux/linux-yocto-4.9.21/0093-x86-amd-don-t-set-X86_BUG_SYSRET_SS_ATTRS-when-runni.patch
new file mode 100644
index 00000000..e2416627
--- /dev/null
+++ b/common/recipes-kernel/linux/linux-yocto-4.9.21/0093-x86-amd-don-t-set-X86_BUG_SYSRET_SS_ATTRS-when-runni.patch
@@ -0,0 +1,65 @@
+From 7a5ded1f7c88ae162c525486f4be8030fa54fa26 Mon Sep 17 00:00:00 2001
+From: Juergen Gross <jgross@suse.com>
+Date: Wed, 30 May 2018 13:09:58 +0200
+Subject: [PATCH 93/93] x86/amd: don't set X86_BUG_SYSRET_SS_ATTRS when running
+ under Xen
+
+Upstream commit: def9331a12977770cc6132d79f8e6565871e8e38 ("x86/amd:
+don't set X86_BUG_SYSRET_SS_ATTRS when running under Xen")
+
+When running as Xen pv guest X86_BUG_SYSRET_SS_ATTRS must not be set
+on AMD cpus.
+
+This bug/feature bit is kind of special as it will be used very early
+when switching threads. Setting the bit and clearing it a little bit
+later leaves a critical window where things can go wrong. This time
+window has enlarged a little bit by using setup_clear_cpu_cap() instead
+of the hypervisor's set_cpu_features callback. It seems this larger
+window now makes it rather easy to hit the problem.
+
+The proper solution is to never set the bit in case of Xen.
+
+Signed-off-by: Juergen Gross <jgross@suse.com>
+Reviewed-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
+Acked-by: Thomas Gleixner <tglx@linutronix.de>
+Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
+---
+ arch/x86/kernel/cpu/amd.c | 5 +++--
+ arch/x86/xen/enlighten.c | 4 +---
+ 2 files changed, 4 insertions(+), 5 deletions(-)
+
+diff --git a/arch/x86/kernel/cpu/amd.c b/arch/x86/kernel/cpu/amd.c
+index cd0abf8..4c2be99 100644
+--- a/arch/x86/kernel/cpu/amd.c
++++ b/arch/x86/kernel/cpu/amd.c
+@@ -857,8 +857,9 @@ static void init_amd(struct cpuinfo_x86 *c)
+ if (cpu_has(c, X86_FEATURE_3DNOW) || cpu_has(c, X86_FEATURE_LM))
+ set_cpu_cap(c, X86_FEATURE_3DNOWPREFETCH);
+
+- /* AMD CPUs don't reset SS attributes on SYSRET */
+- set_cpu_bug(c, X86_BUG_SYSRET_SS_ATTRS);
++ /* AMD CPUs don't reset SS attributes on SYSRET, Xen does. */
++ if (!cpu_has(c, X86_FEATURE_XENPV))
++ set_cpu_bug(c, X86_BUG_SYSRET_SS_ATTRS);
+ }
+
+ #ifdef CONFIG_X86_32
+diff --git a/arch/x86/xen/enlighten.c b/arch/x86/xen/enlighten.c
+index 01120da..fc63c84 100644
+--- a/arch/x86/xen/enlighten.c
++++ b/arch/x86/xen/enlighten.c
+@@ -472,10 +472,8 @@ static void __init xen_init_cpuid_mask(void)
+
+ static void __init xen_init_capabilities(void)
+ {
+- if (xen_pv_domain()) {
+- setup_clear_cpu_cap(X86_BUG_SYSRET_SS_ATTRS);
++ if (xen_pv_domain())
+ setup_force_cpu_cap(X86_FEATURE_XENPV);
+- }
+ }
+
+ static void xen_set_debugreg(int reg, unsigned long val)
+--
+2.7.4
+