Re: [Patch V1] x86, mce: Ensure offline CPU's don't participate in mce rendezvous process.

Re: [Patch V1] x86, mce: Ensure offline CPU's don't participate in mce rendezvous process.

[Borislav Petkov]

On Fri, Dec 04, 2015 at 06:57:31PM -0500, Ashok Raj wrote:
> Linux has logical cpu offline capability. That can be triggered by:
> 
> # echo 0 > /sys/devices/system/cpu/cpuX/online
> 
> In Intel Architecture, MCE's are broadcasted to all CPUs in the system.
> 
> This includes the CPUs marked offline by Linux. Unless the CPU's were removed
> via an ACPI notification, in which case the cpu's are removed from the
> cpu_present_map.
> 
> This patch ensures offline CPU's don't participate in MCE rendezvous, but
> simply perform clearing some status bits to ensure a second MCE wont cause
> automatic shutdown.
> 
> Without the patch, mce_start will increment mce_callin, but mce_start would
> only wait for all online_cpus. So offline cpu's should avoid participating
> in the rendezvous process.
> 
> Reviewed-by: Tony Luck <tony.luck@intel.com>
> Cc: stable@vger.kernel.org
> Signed-off-by: Ashok Raj <ashok.raj@intel.com>
> ---
>  arch/x86/kernel/cpu/mcheck/mce.c | 15 ++++++++++++++-
>  1 file changed, 14 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/x86/kernel/cpu/mcheck/mce.c b/arch/x86/kernel/cpu/mcheck/mce.c
> index c5b0d56..72ea044 100644
> --- a/arch/x86/kernel/cpu/mcheck/mce.c
> +++ b/arch/x86/kernel/cpu/mcheck/mce.c
> @@ -998,7 +998,20 @@ void do_machine_check(struct pt_regs *regs, long error_code)
>  	u64 recover_paddr = ~0ull;
>  	int flags = MF_ACTION_REQUIRED;
>  	int lmce = 0;
> +	unsigned int cpu = smp_processor_id();
>  
> +	/*
> +	 * if this cpu is offline, just bail out.
> +	 */
> +	if (cpu_is_offline(cpu)) {
> +		u64 mcgstatus;
> +
> +		mcgstatus = mce_rdmsrl(MSR_IA32_MCG_STATUS);
> +		if (mcgstatus & MCG_STATUS_RIPV) {
> +			mce_wrmsrl(MSR_IA32_MCG_STATUS, 0);
> +			return;
> +		}
> +	}
>  	ist_enter(regs);
>  
>  	this_cpu_inc(mce_exception_count);
> @@ -1142,8 +1155,8 @@ void do_machine_check(struct pt_regs *regs, long error_code)
>  
>  	if (worst > 0)
>  		mce_report_event(regs);
> -	mce_wrmsrl(MSR_IA32_MCG_STATUS, 0);
>  out:
> +	mce_wrmsrl(MSR_IA32_MCG_STATUS, 0);
>  	sync_core();
>  
>  	if (recover_paddr == ~0ull)
> -- 

With that hunk here you want to clear MSR_IA32_MCG_STATUS in the
!cfg->banks case, right?

If so, this should be a separate patch. Also, CC: stable with an
explanation why.

Thanks.

-- 
Regards/Gruss,
    Boris.

SUSE Linux GmbH, GF: Felix Imendörffer, Jane Smithard, Graham Norton, HRB 21284 (AG Nürnberg)
-- 

RE: [Patch V1] x86, mce: Ensure offline CPU's don't participate in mce rendezvous process.

[Luck, Tony]

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> With that hunk here you want to clear MSR_IA32_MCG_STATUS in the
> !cfg->banks case, right?

I can't imagine how we'd get into do_machine_check without any banks.

Would indeed be a separate patch ... but value seems limited.

-Tony
 
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Re: [Patch V1] x86, mce: Ensure offline CPU's don't participate in mce rendezvous process.

[Borislav Petkov]

On Fri, Dec 04, 2015 at 11:11:12PM +0000, Luck, Tony wrote:
> > With that hunk here you want to clear MSR_IA32_MCG_STATUS in the
> > !cfg->banks case, right?
> 
> I can't imagine how we'd get into do_machine_check without any banks.
> 
> Would indeed be a separate patch ... but value seems limited.

Then we should kill that hunk. I'm all for not covering improbable
cases.

-- 
Regards/Gruss,
    Boris.

SUSE Linux GmbH, GF: Felix Imendörffer, Jane Smithard, Graham Norton, HRB 21284 (AG Nürnberg)
-- 

[Patch V1] x86, mce: Ensure offline CPU's don't participate in mce rendezvous process.

[Ashok Raj]

Linux has logical cpu offline capability. That can be triggered by:

# echo 0 > /sys/devices/system/cpu/cpuX/online

In Intel Architecture, MCE's are broadcasted to all CPUs in the system.

This includes the CPUs marked offline by Linux. Unless the CPU's were removed
via an ACPI notification, in which case the cpu's are removed from the
cpu_present_map.

This patch ensures offline CPU's don't participate in MCE rendezvous, but
simply perform clearing some status bits to ensure a second MCE wont cause
automatic shutdown.

Without the patch, mce_start will increment mce_callin, but mce_start would
only wait for all online_cpus. So offline cpu's should avoid participating
in the rendezvous process.

Reviewed-by: Tony Luck <tony.luck@intel.com>
Cc: stable@vger.kernel.org
Signed-off-by: Ashok Raj <ashok.raj@intel.com>
---
 arch/x86/kernel/cpu/mcheck/mce.c | 15 ++++++++++++++-
 1 file changed, 14 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kernel/cpu/mcheck/mce.c b/arch/x86/kernel/cpu/mcheck/mce.c
index c5b0d56..72ea044 100644
--- a/arch/x86/kernel/cpu/mcheck/mce.c
+++ b/arch/x86/kernel/cpu/mcheck/mce.c
@@ -998,7 +998,20 @@ void do_machine_check(struct pt_regs *regs, long error_code)
 	u64 recover_paddr = ~0ull;
 	int flags = MF_ACTION_REQUIRED;
 	int lmce = 0;
+	unsigned int cpu = smp_processor_id();
 
+	/*
+	 * if this cpu is offline, just bail out.
+	 */
+	if (cpu_is_offline(cpu)) {
+		u64 mcgstatus;
+
+		mcgstatus = mce_rdmsrl(MSR_IA32_MCG_STATUS);
+		if (mcgstatus & MCG_STATUS_RIPV) {
+			mce_wrmsrl(MSR_IA32_MCG_STATUS, 0);
+			return;
+		}
+	}
 	ist_enter(regs);
 
 	this_cpu_inc(mce_exception_count);
@@ -1142,8 +1155,8 @@ void do_machine_check(struct pt_regs *regs, long error_code)
 
 	if (worst > 0)
 		mce_report_event(regs);
-	mce_wrmsrl(MSR_IA32_MCG_STATUS, 0);
 out:
+	mce_wrmsrl(MSR_IA32_MCG_STATUS, 0);
 	sync_core();
 
 	if (recover_paddr == ~0ull)
-- 
2.4.3