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| Started by | Juergen Gross <jgross@suse.com> |
|---|---|
| First post | 2017-04-27 07:10 +0200 |
| Last post | 2017-05-11 14:50 +0200 |
| Articles | 5 — 3 participants |
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[PATCH v3] x86/amd: don't set X86_BUG_SYSRET_SS_ATTRS when running under Xen Juergen Gross <jgross@suse.com> - 2017-04-27 07:10 +0200
Re: [PATCH v3] x86/amd: don't set X86_BUG_SYSRET_SS_ATTRS when running under Xen Juergen Gross <jgross@suse.com> - 2017-05-05 07:10 +0200
Re: [PATCH v3] x86/amd: don't set X86_BUG_SYSRET_SS_ATTRS when running under Xen Boris Ostrovsky <boris.ostrovsky@oracle.com> - 2017-05-05 18:10 +0200
Re: [PATCH v3] x86/amd: don't set X86_BUG_SYSRET_SS_ATTRS when running under Xen Juergen Gross <jgross@suse.com> - 2017-05-11 12:40 +0200
Re: [PATCH v3] x86/amd: don't set X86_BUG_SYSRET_SS_ATTRS when running under Xen Thomas Gleixner <tglx@linutronix.de> - 2017-05-11 14:50 +0200
| From | Juergen Gross <jgross@suse.com> |
|---|---|
| Date | 2017-04-27 07:10 +0200 |
| Subject | [PATCH v3] x86/amd: don't set X86_BUG_SYSRET_SS_ATTRS when running under Xen |
| Message-ID | <tAJQK-4gp-7@gated-at.bofh.it> |
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>
---
arch/x86/kernel/cpu/amd.c | 5 +++--
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 a1af4f68278f..dcfd07faf1c3 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);
--
2.12.0
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| From | Juergen Gross <jgross@suse.com> |
|---|---|
| Date | 2017-05-05 07:10 +0200 |
| Subject | Re: [PATCH v3] x86/amd: don't set X86_BUG_SYSRET_SS_ATTRS when running under Xen |
| Message-ID | <tDDF7-5EL-1@gated-at.bofh.it> |
| In reply to | #1631861 |
Any comments?
Juergen
On 27/04/17 07:01, Juergen Gross wrote:
> 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>
> ---
> arch/x86/kernel/cpu/amd.c | 5 +++--
> 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 a1af4f68278f..dcfd07faf1c3 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);
>
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| From | Boris Ostrovsky <boris.ostrovsky@oracle.com> |
|---|---|
| Date | 2017-05-05 18:10 +0200 |
| Subject | Re: [PATCH v3] x86/amd: don't set X86_BUG_SYSRET_SS_ATTRS when running under Xen |
| Message-ID | <tDNXP-402-1@gated-at.bofh.it> |
| In reply to | #1636163 |
On 05/05/2017 01:09 AM, Juergen Gross wrote:
> Any comments?
>
>
> Juergen
>
> On 27/04/17 07:01, Juergen Gross wrote:
>> 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.
FWIW,
Reviewed-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
>>
>> Signed-off-by: Juergen Gross <jgross@suse.com>
>> ---
>> arch/x86/kernel/cpu/amd.c | 5 +++--
>> 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 a1af4f68278f..dcfd07faf1c3 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);
>>
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| From | Juergen Gross <jgross@suse.com> |
|---|---|
| Date | 2017-05-11 12:40 +0200 |
| Subject | Re: [PATCH v3] x86/amd: don't set X86_BUG_SYSRET_SS_ATTRS when running under Xen |
| Message-ID | <tFTFL-59I-7@gated-at.bofh.it> |
| In reply to | #1631861 |
On 27/04/17 07:01, Juergen Gross wrote:
> 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>
Any objections for carrying this through the Xen tree?
Juergen
> ---
> arch/x86/kernel/cpu/amd.c | 5 +++--
> 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 a1af4f68278f..dcfd07faf1c3 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);
>
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| From | Thomas Gleixner <tglx@linutronix.de> |
|---|---|
| Date | 2017-05-11 14:50 +0200 |
| Subject | Re: [PATCH v3] x86/amd: don't set X86_BUG_SYSRET_SS_ATTRS when running under Xen |
| Message-ID | <tFVHA-6lJ-23@gated-at.bofh.it> |
| In reply to | #1639299 |
On Thu, 11 May 2017, Juergen Gross wrote: > On 27/04/17 07:01, Juergen Gross wrote: > > 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> > > Any objections for carrying this through the Xen tree? Acked-by: Thomas Gleixner <tglx@linutronix.de>
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