A change introduced with commit 60283df7ac
("x86/apic: Read Error Status Register correctly") removed a read from the
APIC ESR register made before writing to same required to retrieve the
correct error status on Pentium systems affected by the 3AP erratum[1]:
"3AP. Writes to Error Register Clears Register
PROBLEM: The APIC Error register is intended to only be read.
If there is a write to this register the data in the APIC Error
register will be cleared and lost.
IMPLICATION: There is a possibility of clearing the Error
register status since the write to the register is not
specifically blocked.
WORKAROUND: Writes should not occur to the Pentium processor
APIC Error register.
STATUS: For the steppings affected see the Summary Table of
Changes at the beginning of this section."
The steppings affected are actually: B1, B3 and B5.
To avoid this information loss this change avoids the write to
ESR on all Pentium systems where it is actually never needed;
in Pentium processor documentation ESR was noted read-only and
the write only required for future architectural
compatibility[2].
The approach taken is the same as in lapic_setup_esr().
References:
[1] "Pentium Processor Family Developer's Manual", Intel Corporation,
1997, order number 241428-005, Appendix A "Errata and S-Specs for the
Pentium Processor Family", p. A-92,
[2] "Pentium Processor Family Developer's Manual, Volume 3: Architecture
and Programming Manual", Intel Corporation, 1995, order number
241430-004, Section 19.3.3. "Error Handling In APIC", p. 19-33.
Signed-off-by: Maciej W. Rozycki <macro@linux-mips.org>
Cc: Richard Weinberger <richard@nod.at>
Link: http://lkml.kernel.org/r/alpine.LFD.2.11.1404011300010.27402@eddie.linux-mips.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
023de4a09f