[PATCH v4 00/12] APEI in_nmi() rework and arm64 SDEI wire-up

[James Morse]

The aim of this series is to wire arm64's SDEI into APEI.

Since v3 the NMI fixmap entries and locks have moved into their own
structure. This moves the indirection up from the 'lock', which should
be more acceptible to polite society.
Changes are noted in each patch.

This touches a few trees, so I'm not sure how best it should be merged.
Patches 11 and 12 are reducing a race that is made worse by patch 4, I'd
like them to arrive together, even though patch 11 doesn't depend on anything
else in the series. A partial merge of this would  be 1-3 and 11.


The earlier boiler-plate:

What's SDEI? Its ARM's "Software Delegated Exception Interface" [0]. It's
used by firmware to tell the OS about firmware-first RAS events.

These Software exceptions can interrupt anything, so I describe them as
NMI-like. They aren't the only NMI-like way to notify the OS about
firmware-first RAS events, the ACPI spec also defines 'NOTFIY_SEA' and
'NOTIFY_SEI'.

(Acronyms: SEA, Synchronous External Abort. The CPU requested some memory,
but the owner of that memory said no. These are always synchronous with the
instruction that caused them. SEI, System-Error Interrupt, commonly called
SError. This is an asynchronous external abort, the memory-owner didn't say no
at the right point. Collectively these things are called external-aborts
How is firmware involved? It traps these and re-injects them into the kernel
once its written the CPER records).

APEI's GHES code only expects one source of NMI. If a platform implements
more than one of these mechanisms, APEI needs to handle the interaction.
'SEA' and 'SEI' can interact as 'SEI' is asynchronous. SDEI can interact
with itself: its exceptions can be 'normal' or 'critical', and firmware
could use both types for RAS. (errors using normal, 'panic-now' using
critical).

What does this series do?
Patches 1-4 refactor APEIs 'estatus queue' so it can be used for all
NMI-like notifications. This defers the NMI work to irq_work, which will
happen when we next unmask interrupts.

Patches 5&6 move the arch and KVM code around so that NMI-like notifications
are always called in_nmi().

Patch 7 changes the 'irq or nmi?' path through ghes_copy_tofrom_phys()
to be per-ghes. When called in_nmi(), the struct ghes is expected to
provide a fixmap slot and lock that is safe to use. NMI-like notifications
that mask each other can share these resources. Those that interact should
have their own fixmap slot and lock.

Patch 8 renames NOTIFY_SEA's use of NOTIFY_NMI's infrastructure, as we're
about to have multiple NMI-like users that can't share resources.

Pathes 9&10 add the SDEI helper, and notify methods for APEI.

After this, adding further firmware-first pieces for arm64 is simple
(and safe), and all our NMI-like notifications behave the same as x86's
NOTIFY_NMI.

All of this makes the race between memory_failure_queue() and
ret_to_user worse, as there is now always irq_work involved.

Patch 11 makes the reschedule to memory_failure() run as soon as possible.
Patch 12 makes sure the arch code knows whether the irq_work has run by
the time do_sea() returns. We can skip the signalling step if it has as
APEI has done its work.


ghes.c became clearer to me when I worked out that it has three sets of
functions with 'estatus' in the name. One is a pool of memory that can be
allocated-from atomically. This is grown/shrunk when new NMI users are
allocated.
The second is the estatus-cache, which holds recent notifications so it
can suppress notifications we've already handled.
The last it the estatus-queue, which holds data from NMI-like notifications
(in pool memory) to be processed from irq_work.


Testing?
Tested with the SDEI FVP based software model and a mocked up NOTFIY_SEA using
KVM. I've added a case where 'corrected errors' are discovered at probe time
to exercise ghes_probe() during boot. I've only build tested this on x86.


Thanks,

James

[0] http://infocenter.arm.com/help/topic/com.arm.doc.den0054a/ARM_DEN0054A_Software_Delegated_Exception_Interface.pdf



James Morse (12):
  ACPI / APEI: Move the estatus queue code up, and under its own ifdef
  ACPI / APEI: Generalise the estatus queue's add/remove and notify code
  ACPI / APEI: don't wait to serialise with oops messages when
    panic()ing
  ACPI / APEI: Switch NOTIFY_SEA to use the estatus queue
  KVM: arm/arm64: Add kvm_ras.h to collect kvm specific RAS plumbing
  arm64: KVM/mm: Move SEA handling behind a single 'claim' interface
  ACPI / APEI: Make the nmi_fixmap_idx per-ghes to allow multiple
    in_nmi() users
  ACPI / APEI: Split fixmap pages for arm64 NMI-like notifications
  firmware: arm_sdei: Add ACPI GHES registration helper
  ACPI / APEI: Add support for the SDEI GHES Notification type
  mm/memory-failure: increase queued recovery work's priority
  arm64: acpi: Make apei_claim_sea() synchronise with APEI's irq work

 arch/arm/include/asm/kvm_ras.h       |  14 +
 arch/arm/include/asm/system_misc.h   |   5 -
 arch/arm64/include/asm/acpi.h        |   4 +
 arch/arm64/include/asm/daifflags.h   |   1 +
 arch/arm64/include/asm/fixmap.h      |   8 +-
 arch/arm64/include/asm/kvm_ras.h     |  24 ++
 arch/arm64/include/asm/system_misc.h |   2 -
 arch/arm64/kernel/acpi.c             |  49 ++++
 arch/arm64/mm/fault.c                |  30 +-
 drivers/acpi/apei/ghes.c             | 518 ++++++++++++++++++++---------------
 drivers/firmware/arm_sdei.c          |  67 +++++
 include/acpi/ghes.h                  |  17 ++
 include/linux/arm_sdei.h             |   8 +
 mm/memory-failure.c                  |  11 +-
 virt/kvm/arm/mmu.c                   |   4 +-
 15 files changed, 503 insertions(+), 259 deletions(-)
 create mode 100644 arch/arm/include/asm/kvm_ras.h
 create mode 100644 arch/arm64/include/asm/kvm_ras.h

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2.16.2