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SubjectRe: [PATCH 2/2 v2] x86, mce: support memory error recovery for both UCNA and Deferred error in machine_check_poll
On Wed, Nov 05, 2014 at 12:47:53PM +0800, Chen Yucong wrote:
> Uncorrected no action required (UCNA) - is a UCR error that is not

Please explain "UCR" if you're using it out of the rest of the SDM text.

> signaled via a machine check exception and, instead, is reported to
> system software as a corrected machine check error. UCNA errors indicate
> that some data in the system is corrupted, but the data has not been
> consumed and the processor state is valid and you may continue execution
> on this processor. UCNA errors require no action from system software
> to continue execution. Note that UCNA errors are supported by the
> processor only when IA32_MCG_CAP[24] (MCG_SER_P) is set.
> -- Intel SDM Volume 3B
>
> Deferred errors are errors that cannot be corrected by hardware, but
> do not cause an immediate interruption in program flow, loss of data
> integrity, or corruption of processor state. These errors indicate
> that data has been corrupted but not consumed. Hardware writes information
> to the status and address registers in the corresponding bank that
> identifies the source of the error if deferred errors are enabled for
> logging. Deferred errors are not reported via machine check exceptions;
> they can be seen by polling the MCi_STATUS registers.
> -- ADM64 APM Volume 2
^^^

Please try to spell "AMD" correctly. Your first patch has "ADM" too.

>
> Above two items, both UCNA and Deferred errors belong to detected
> errors, but they can't be corrected by hardware, and this is very
> similar to Software Recoverable Action Optional (SRAO) errors.
> Therefore, we can take some actions that have been used for handling
> SRAO errors to handle UCNA and Deferred errors.


>
> Signed-off-by: Chen Yucong <slaoub@gmail.com>
> ---
> arch/x86/kernel/cpu/mcheck/mce.c | 50 ++++++++++++++++++++++++++++++++++++++
> 1 file changed, 50 insertions(+)
>
> diff --git a/arch/x86/kernel/cpu/mcheck/mce.c b/arch/x86/kernel/cpu/mcheck/mce.c
> index 453e9bf..37f7649 100644
> --- a/arch/x86/kernel/cpu/mcheck/mce.c
> +++ b/arch/x86/kernel/cpu/mcheck/mce.c
> @@ -575,6 +575,46 @@ static void mce_read_aux(struct mce *m, int i)
> }
> }
>
> +static bool mem_deferred_error(struct mce *m)
> +{
> + int severity;
> + struct cpuinfo_x86 *c = &boot_cpu_data;
> +
> + severity = mce_severity(m, mca_cfg.tolerant, NULL, false);
> +
> + if (c->x86_vendor == X86_VENDOR_AMD) {
> + /*
> + * AMD BKDGs - Machine Check Error Codes
> + *
> + * Bit 8 of ErrCode[15:0] of MCi_STATUS is used for indicating
> + * a memory-specific error. Note that this field encodes info-
> + * rmation about memory-hierarchy level involved in the error.
> + */
> + if (severity == MCE_DEFERRED_SEVERITY)
> + return (m->status & 0xff00) == BIT(8);
> + } else if (c->x86_vendor == X86_VENDOR_INTEL) {
> + /*
> + * Intel SDM Volume 3B - 15.9.2 Compound Error Codes
> + *
> + * Bit 7 of the MCACOD field of IA32_MCi_STATUS is used for
> + * indicating a memory error. Bit 8 is used for indicating a
> + * cache hierarchy error. The combination of bit 2 and bit 3
> + * is used for indicating a `generic' cache hierarchy error
> + * But we can't just blindly check the above bits, because if
> + * bit 11 is set, then it is a bus/interconnect error - and
> + * either way the above bits just gives more detail on what
> + * bus/interconnect error happened. Note that bit 12 can be
> + * ignored, as it's the "filter" bit.
> + */
> + if (severity == MCE_UCNA_SEVERITY)
> + return (m->status & 0xef80) == BIT(7) ||
> + (m->status & 0xef00) == BIT(8) ||
> + (m->status & 0xeffc) == 0xc;
> + }
> +
> + return false;
> +}

This function is combining deferred and memory error checks. Please do
this differently:

if (memory_error(m))
if (deferred_error(m))
blabla

so that the memory_error() function can be used in other code paths
separately.

--
Regards/Gruss,
Boris.

Sent from a fat crate under my desk. Formatting is fine.
--


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