x86, x2apic: Enable the bios request for x2apic optout
authorSuresh Siddha <suresh.b.siddha@intel.com>
Wed, 24 Aug 2011 00:05:18 +0000 (17:05 -0700)
committerIngo Molnar <mingo@elte.hu>
Wed, 21 Sep 2011 08:21:50 +0000 (10:21 +0200)
commit41750d31fc9599fd81763e685a6b7b42d298c4f8
tree6cacc746aa159c8bd08f151270f0bffe126caa9d
parent9d037a777695993ec7437e5f451647dea7919d4c
x86, x2apic: Enable the bios request for x2apic optout

On the platforms which are x2apic and interrupt-remapping
capable, Linux kernel is enabling x2apic even if the BIOS
doesn't. This is to take advantage of the features that x2apic
brings in.

Some of the OEM platforms are running into issues because of
this, as their bios is not x2apic aware. For example, this was
resulting in interrupt migration issues on one of the platforms.
Also if the BIOS SMI handling uses APIC interface to send SMI's,
then the BIOS need to be aware of x2apic mode that OS has
enabled.

On some of these platforms, BIOS doesn't have a HW mechanism to
turnoff the x2apic feature to prevent OS from enabling it.

To resolve this mess, recent changes to the VT-d2 specification:

 http://download.intel.com/technology/computing/vptech/Intel(r)_VT_for_Direct_IO.pdf

includes a mechanism that provides BIOS a way to request system
software to opt out of enabling x2apic mode.

Look at the x2apic optout flag in the DMAR tables before
enabling the x2apic mode in the platform. Also print a warning
that we have disabled x2apic based on the BIOS request.

Kernel boot parameter "intremap=no_x2apic_optout" can be used to
override the BIOS x2apic optout request.

Signed-off-by: Youquan Song <youquan.song@intel.com>
Signed-off-by: Suresh Siddha <suresh.b.siddha@intel.com>
Cc: yinghai@kernel.org
Cc: joerg.roedel@amd.com
Cc: tony.luck@intel.com
Cc: dwmw2@infradead.org
Link: http://lkml.kernel.org/r/20110824001456.171766616@sbsiddha-desk.sc.intel.com
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Documentation/kernel-parameters.txt
arch/x86/kernel/apic/apic.c
drivers/iommu/dmar.c
drivers/iommu/intr_remapping.c
include/linux/dmar.h