From 023de4a09f571fad0af9691e4e437e14b68f05fb Mon Sep 17 00:00:00 2001 From: "Maciej W. Rozycki" Date: Tue, 1 Apr 2014 13:30:21 +0100 Subject: [PATCH] x86/apic: Reinstate error IRQ Pentium erratum 3AP workaround A change introduced with commit 60283df7ac26a4fe2d56631ca2946e04725e7eaf ("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 Cc: Richard Weinberger Link: http://lkml.kernel.org/r/alpine.LFD.2.11.1404011300010.27402@eddie.linux-mips.org Signed-off-by: Ingo Molnar --- arch/x86/kernel/apic/apic.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/arch/x86/kernel/apic/apic.c b/arch/x86/kernel/apic/apic.c index 53e20531470e..005ed3fb0391 100644 --- a/arch/x86/kernel/apic/apic.c +++ b/arch/x86/kernel/apic/apic.c @@ -1996,7 +1996,8 @@ static inline void __smp_error_interrupt(struct pt_regs *regs) }; /* First tickle the hardware, only then report what went on. -- REW */ - apic_write(APIC_ESR, 0); + if (lapic_get_maxlvt() > 3) /* Due to the Pentium erratum 3AP. */ + apic_write(APIC_ESR, 0); v = apic_read(APIC_ESR); ack_APIC_irq(); atomic_inc(&irq_err_count); -- 2.20.1