This is a note to let you know that I've just added the patch titled
x86/amd: don't set X86_BUG_SYSRET_SS_ATTRS when running under Xen
to the 4.9-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
x86-amd-don-t-set-x86_bug_sysret_ss_attrs-when-running-under-xen.patch
and it can be found in the queue-4.9 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <sta...@vger.kernel.org> know about it.
From foo@baz Sat Jun 2 15:10:07 CEST 2018
From: Juergen Gross <jgr...@suse.com>
Date: Wed, 30 May 2018 13:09:58 +0200
Subject: x86/amd: don't set X86_BUG_SYSRET_SS_ATTRS when running under Xen
To: sta...@vger.kernel.org, xen-devel@lists.xenproject.org
Cc: d...@amazon.co.uk, boris.ostrov...@oracle.com, Juergen Gross
<jgr...@suse.com>
Message-ID: <20180530110958.19413-4-jgr...@suse.com>
From: Juergen Gross <jgr...@suse.com>
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 <jgr...@suse.com>
Reviewed-by: Boris Ostrovsky <boris.ostrov...@oracle.com>
Acked-by: Thomas Gleixner <t...@linutronix.de>
Signed-off-by: Greg Kroah-Hartman <gre...@linuxfoundation.org>
---
arch/x86/kernel/cpu/amd.c | 5 +++--
arch/x86/xen/enlighten.c | 4 +---
2 files changed, 4 insertions(+), 5 deletions(-)
--- 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
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
--- a/arch/x86/xen/enlighten.c
+++ b/arch/x86/xen/enlighten.c
@@ -473,10 +473,8 @@ static void __init xen_init_cpuid_mask(v
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)
Patches currently in stable-queue which might be from jgr...@suse.com are
queue-4.9/x86-amd-don-t-set-x86_bug_sysret_ss_attrs-when-running-under-xen.patch
queue-4.9/x86-amd-revert-commit-944e0fc51a89c9827b9.patch
queue-4.9/xen-set-cpu-capabilities-from-xen_start_kernel.patch
_______________________________________________
Xen-devel mailing list
Xen-devel@lists.xenproject.org
https://lists.xenproject.org/mailman/listinfo/xen-devel
