Above commit is a wrong backport, as it is based on a missing prerequisite patch. Correct that by reverting said commit, include the missing patch, and do the backport correctly.
Juergen Gross (3): x86/amd: revert commit 944e0fc51a89c9827b98813d65dc083274777c7f xen: set cpu capabilities from xen_start_kernel() x86/amd: don't set X86_BUG_SYSRET_SS_ATTRS when running under Xen
arch/x86/xen/enlighten.c | 14 +++++++------- 1 file changed, 7 insertions(+), 7 deletions(-)
Revert commit 944e0fc51a89c9827b98813d65dc083274777c7f ("x86/amd: don't set X86_BUG_SYSRET_SS_ATTRS when running under Xen") as it is lacking a prerequisite patch and is making things worse.
Signed-off-by: Juergen Gross jgross@suse.com --- arch/x86/kernel/cpu/amd.c | 5 ++--- arch/x86/xen/enlighten.c | 4 +++- 2 files changed, 5 insertions(+), 4 deletions(-)
diff --git a/arch/x86/kernel/cpu/amd.c b/arch/x86/kernel/cpu/amd.c index 4c2be99fa0fb..cd0abf8ed314 100644 --- a/arch/x86/kernel/cpu/amd.c +++ b/arch/x86/kernel/cpu/amd.c @@ -857,9 +857,8 @@ 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, Xen does. */ - if (!cpu_has(c, X86_FEATURE_XENPV)) - set_cpu_bug(c, X86_BUG_SYSRET_SS_ATTRS); + /* AMD CPUs don't reset SS attributes on SYSRET */ + 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 081437b5f381..2bea87cc0ff2 100644 --- a/arch/x86/xen/enlighten.c +++ b/arch/x86/xen/enlighten.c @@ -1977,8 +1977,10 @@ EXPORT_SYMBOL_GPL(xen_hvm_need_lapic);
static void xen_set_cpu_features(struct cpuinfo_x86 *c) { - if (xen_pv_domain()) + if (xen_pv_domain()) { + clear_cpu_bug(c, X86_BUG_SYSRET_SS_ATTRS); set_cpu_cap(c, X86_FEATURE_XENPV); + } }
static void xen_pin_vcpu(int cpu)
There is no need to set the same capabilities for each cpu individually. This can easily be done for all cpus when starting the kernel.
Upstream commit: 0808e80cb760de2733c0527d2090ed2205a1eef8 ("xen: set cpu capabilities from xen_start_kernel()")
Signed-off-by: Juergen Gross jgross@suse.com Reviewed-by: Boris Ostrovsky boris.ostrovsky@oracle.com --- arch/x86/xen/enlighten.c | 18 +++++++++--------- 1 file changed, 9 insertions(+), 9 deletions(-)
diff --git a/arch/x86/xen/enlighten.c b/arch/x86/xen/enlighten.c index 2bea87cc0ff2..fb1867fedd29 100644 --- a/arch/x86/xen/enlighten.c +++ b/arch/x86/xen/enlighten.c @@ -471,6 +471,14 @@ static void __init xen_init_cpuid_mask(void) cpuid_leaf1_ecx_set_mask = (1 << (X86_FEATURE_MWAIT % 32)); }
+static void __init xen_init_capabilities(void) +{ + if (xen_pv_domain()) { + setup_clear_cpu_cap(X86_BUG_SYSRET_SS_ATTRS); + setup_force_cpu_cap(X86_FEATURE_XENPV); + } +} + static void xen_set_debugreg(int reg, unsigned long val) { HYPERVISOR_set_debugreg(reg, val); @@ -1631,6 +1639,7 @@ asmlinkage __visible void __init xen_start_kernel(void)
xen_init_irq_ops(); xen_init_cpuid_mask(); + xen_init_capabilities();
#ifdef CONFIG_X86_LOCAL_APIC /* @@ -1975,14 +1984,6 @@ bool xen_hvm_need_lapic(void) } EXPORT_SYMBOL_GPL(xen_hvm_need_lapic);
-static void xen_set_cpu_features(struct cpuinfo_x86 *c) -{ - if (xen_pv_domain()) { - clear_cpu_bug(c, X86_BUG_SYSRET_SS_ATTRS); - set_cpu_cap(c, X86_FEATURE_XENPV); - } -} - static void xen_pin_vcpu(int cpu) { static bool disable_pinning; @@ -2029,7 +2030,6 @@ const struct hypervisor_x86 x86_hyper_xen = { .init_platform = xen_hvm_guest_init, #endif .x2apic_available = xen_x2apic_para_available, - .set_cpu_features = xen_set_cpu_features, .pin_vcpu = xen_pin_vcpu, }; EXPORT_SYMBOL(x86_hyper_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.
Upstream commit: def9331a12977770cc6132d79f8e6565871e8e38 ("x86/amd: don't set X86_BUG_SYSRET_SS_ATTRS when running under Xen")
Signed-off-by: Juergen Gross jgross@suse.com Reviewed-by: Boris Ostrovsky boris.ostrovsky@oracle.com Acked-by: Thomas Gleixner tglx@linutronix.de --- 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 cd0abf8ed314..4c2be99fa0fb 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 fb1867fedd29..a11b46f1abbd 100644 --- a/arch/x86/xen/enlighten.c +++ b/arch/x86/xen/enlighten.c @@ -473,10 +473,8 @@ 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)
On Wed, May 30, 2018 at 01:09:55PM +0200, Juergen Gross wrote:
Above commit is a wrong backport, as it is based on a missing prerequisite patch. Correct that by reverting said commit, include the missing patch, and do the backport correctly.
Juergen Gross (3): x86/amd: revert commit 944e0fc51a89c9827b98813d65dc083274777c7f xen: set cpu capabilities from xen_start_kernel() x86/amd: don't set X86_BUG_SYSRET_SS_ATTRS when running under Xen
All now queued up, thanks.
greg k-h
linux-stable-mirror@lists.linaro.org
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Greg KH -
Juergen Gross