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| author | Juergen Gross <jgross@suse.com> | 2017-04-27 07:01:20 +0200 |
|---|---|---|
| committer | Juergen Gross <jgross@suse.com> | 2017-05-11 15:55:14 +0200 |
| commit | def9331a12977770cc6132d79f8e6565871e8e38 (patch) | |
| tree | e060cefab582b280d97681608d15bb959050b0d4 /arch | |
| parent | d162809f85b4f54ef075517ffa2f3d02e55d5a53 (diff) | |
| download | linux-def9331a12977770cc6132d79f8e6565871e8e38.tar.gz | |
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: Juergen Gross <jgross@suse.com>
Diffstat (limited to 'arch')
| -rw-r--r-- | arch/x86/kernel/cpu/amd.c | 5 | ||||
| -rw-r--r-- | arch/x86/xen/enlighten_pv.c | 1 |
2 files changed, 3 insertions, 3 deletions
diff --git a/arch/x86/kernel/cpu/amd.c b/arch/x86/kernel/cpu/amd.c index c36140d788fe..b6da6e75e3a8 100644 --- a/arch/x86/kernel/cpu/amd.c +++ b/arch/x86/kernel/cpu/amd.c @@ -799,8 +799,9 @@ 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_pv.c b/arch/x86/xen/enlighten_pv.c index b5c54ab0e195..7cd442690f9d 100644 --- a/arch/x86/xen/enlighten_pv.c +++ b/arch/x86/xen/enlighten_pv.c @@ -290,7 +290,6 @@ static bool __init xen_check_xsave(void) static void __init xen_init_capabilities(void) { - setup_clear_cpu_cap(X86_BUG_SYSRET_SS_ATTRS); setup_force_cpu_cap(X86_FEATURE_XENPV); setup_clear_cpu_cap(X86_FEATURE_DCA); setup_clear_cpu_cap(X86_FEATURE_APERFMPERF); |