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