fix #28612342

commit d44f1b8dd7e66d80cc4205809e5ace866bd851da upstream

To split up APEIs in_nmi() path, the caller needs to always be
in_nmi(). Add a helper to do the work and claim the notification.

When KVM or the arch code takes an exception that might be a RAS
notification, it asks the APEI firmware-first code whether it wants
to claim the exception. A future kernel-first mechanism may be queried
afterwards, and claim the notification, otherwise we fall through
to the existing default behaviour.

The NOTIFY_SEA code was merged before considering multiple, possibly
interacting, NMI-like notifications and the need to consider kernel
first in the future. Make the 'claiming' behaviour explicit.

Restructuring the APEI code to allow multiple NMI-like notifications
means any notification that might interrupt interrupts-masked
code must always be wrapped in nmi_enter()/nmi_exit(). This will
allow APEI to use in_nmi() to use the right fixmap entries.

Mask SError over this window to prevent an asynchronous RAS error
arriving and tripping 'nmi_enter()'s BUG_ON(in_nmi()).
Signed-off-by: NJames Morse <james.morse@arm.com>
Acked-by: NMarc Zyngier <marc.zyngier@arm.com>
Tested-by: NTyler Baicar <tbaicar@codeaurora.org>
Acked-by: NCatalin Marinas <catalin.marinas@arm.com>
Signed-off-by: NRafael J. Wysocki <rafael.j.wysocki@intel.com>
Signed-off-by: NBaolin Wang <baolin.wang@linux.alibaba.com>
Reviewed-by: NAlex Shi <alex.shi@linux.alibaba.com>
Acked-by: NCaspar Zhang <caspar@linux.alibaba.com>
Reviewed-by: Nluanshi <zhangliguang@linux.alibaba.com>