Vol. 3B 15-17

MACHINE-CHECK ARCHITECTURE

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Uncorrected no action required (UCNA) - is a UCR error that is not 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. A UNCA error is indicated with UC=1, PCC=0, S=0 and AR=0 in the IA32_MCi_STATUS register.

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Software recoverable action optional (SRAO) - a UCR error is signaled either via a machine check exception or 
CMCI. System software recovery action is optional and not required to continue execution from this machine 
check exception. SRAO errors indicate that some data in the system is corrupt, but the data has not been 
consumed and the processor state is valid. SRAO errors provide the additional error information for system 
software to perform a recovery action. An SRAO error when signaled as a machine check is indicated with 
UC=1, PCC=0, S=1, EN=1 and AR=0 in the IA32_MCi_STATUS register. In cases when SRAO is signaled via 
CMCI the error signature is indicated via UC=1, PCC=0, S=0. Recovery actions for SRAO errors are MCA error 
code specific. The MISCV and the ADDRV flags in the IA32_MCi_STATUS register are set when the additional 
error information is available from the IA32_MCi_MISC and the IA32_MCi_ADDR registers. System software 
needs to inspect the MCA error code fields in the IA32_MCi_STATUS register to identify the specific recovery 
action for a given SRAO error. If MISCV and ADDRV are not set, it is recommended that no system software 
error recovery be performed however, system software can resume execution.

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Software recoverable action required (SRAR) - a UCR error that requires system software to take a recovery 
action on this processor before scheduling another stream of execution on this processor. SRAR errors indicate 
that the error was detected and raised at the point of the consumption in the execution flow. An SRAR error is 
indicated with UC=1, PCC=0, S=1, EN=1 and AR=1 in the IA32_MCi_STATUS register. Recovery actions are 
MCA error code specific. The MISCV and the ADDRV flags in the IA32_MCi_STATUS register are set when the 
additional error information is available from the IA32_MCi_MISC and the IA32_MCi_ADDR registers. System 
software needs to inspect the MCA error code fields in the IA32_MCi_STATUS register to identify the specific 
recovery action for a given SRAR error. If MISCV and ADDRV are not set, it is recommended that system 
software shutdown the system.

Table 15-6 summarizes UCR, corrected, and uncorrected errors. 

15.6.4 

UCR Error Overwrite Rules

In general, the overwrite rules are as follows:

Table 15-6.  MC Error Classifications

Type of Error

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NOTES:

1. SRAR, SRAO and UCNA errors are supported by the processor only when IA32_MCG_CAP[24] (MCG_SER_P) is set. 

UC EN

PCC

S

AR Signaling Software Action

Example

Uncorrected Error (UC) 1

1

1

x

x

MCE

If EN=1, reset the system, else log 

and OK to keep the system running.

SRAR

1

1

0

1

1

MCE

For known MCACOD, take specific 

recovery action;
For unknown MCACOD, must 

bugcheck.
If OVER=1, reset system, else take 

specific recovery action.

Cache to processor load 

error.

SRAO

1

x

2

2. EN=1, S=1 when signaled via MCE. EN=x, S=0 when signaled via CMC.

0

x

2

0

MCE/CMC For known MCACOD, take specific 

recovery action;
For unknown MCACOD, OK to keep 

the system running.

Patrol scrub and explicit 

writeback poison errors.

UCNA

1

x

0

0

0

CMC

Log the error and Ok to keep the 

system running.

Poison detection error.

Corrected Error (CE)

0

x

x

x

x

CMC

Log the error and no corrective 

action required.

ECC in caches and 

memory.