diff options
| author | David Woodhouse <dwmw@amazon.co.uk> | 2018-07-14 02:33:24 -0700 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2018-07-25 10:18:23 +0200 |
| commit | e57a81c43ca5ea32bf28c4634e903e7a4a1cbbd3 (patch) | |
| tree | a5a127ff0e5c61c5e7911532269db7d42cd66263 | |
| parent | 237a1870da36fcd10f67503928c485d964726d83 (diff) | |
x86/amd: don't set X86_BUG_SYSRET_SS_ATTRS when running under Xen
commit def9331a12977770cc6132d79f8e6565871e8e38 upstream
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>
Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Srivatsa S. Bhat <srivatsa@csail.mit.edu>
Reviewed-by: Matt Helsley (VMware) <matt.helsley@gmail.com>
Reviewed-by: Alexey Makhalov <amakhalov@vmware.com>
Reviewed-by: Bo Gan <ganb@vmware.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
| -rw-r--r-- | arch/x86/kernel/cpu/amd.c | 5 | ||||
| -rw-r--r-- | 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 f4fb8f5b0be4..9b2941422b68 100644 --- a/arch/x86/kernel/cpu/amd.c +++ b/arch/x86/kernel/cpu/amd.c @@ -791,8 +791,9 @@ 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 2d7ab4e23e9e..82fd84d5e1aa 100644 --- a/arch/x86/xen/enlighten.c +++ b/arch/x86/xen/enlighten.c @@ -462,10 +462,8 @@ 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) |