SDEI: Make dispatches synchronous ...

SDEI event dispatches currently only sets up the Non-secure context
before returning to the caller. The actual dispatch only happens upon
exiting EL3 next time.

However, for various error handling scenarios, it's beneficial to have
the dispatch happen synchronously. I.e. when receiving SDEI interrupt,
or for a successful sdei_dispatch_event() call, the event handler is
executed; and upon the event completion, dispatcher execution resumes
after the point of dispatch. The jump primitives introduced in the
earlier patch facilitates this feature.

With this patch:

  - SDEI interrupts and calls to sdei_dispatch_event prepares the NS
    context for event dispatch, then sets a jump point, and immediately
    exits EL3. This results in the client handler executing in
    Non-secure.

  - When the SDEI client completes the dispatched event, the SDEI
    dispatcher does a longjmp to the jump pointer created earlier. For
    the caller of the sdei_dispatch_event() in particular, this would
    appear as if call returned successfully.

The dynamic workaround for CVE_2018_3639 is slightly shifted around as
part of related minor refactoring. It doesn't affect the workaround
functionality.

Documentation updated.

NOTE: This breaks the semantics of the explicit dispatch API, and any
exiting usages should be carefully reviewed.

Change-Id: Ib9c876d27ea2af7fb22de49832e55a0da83da3f9
Signed-off-by: Jeenu Viswambharan <jeenu.viswambharan@arm.com>

SDEI: Determine client EL from NS context's SCR_EL3 ...

Currently, the dispatcher reads from SCR_EL3 register directly to
determine the EL of SDEI client. This is with the assumption that
SCR_EL3 is not modified throughout. However, with RAS work flows, it's
possible that SCR_EL3 register contains values corresponding to Secure
world, and therefore EL determination can go wrong. To mitigate this,
always read the register from the saved Non-secure context.

Change-Id: Ic85e4021deb18eb58757f676f9a001174998543a
Signed-off-by: Jeenu Viswambharan <jeenu.viswambharan@arm.com>

SDEI: Allow platforms to define explicit events ...

The current macros only allow to define dynamic and statically-bound
SDEI events. However, there ought be a mechanism to define SDEI events
that are explicitly dispatched; i.e., events that are dispatched as a
result of a previous secure interrupt or other exception

This patch introduces SDEI_EXPLICIT_EVENT() macro to define an explicit
event. They must be placed under private mappings. Only the priority
flags are allowed to be additionally specified.

Documentation updated.

Change-Id: I2e12f5571381195d6234c9dfbd5904608ad41db3
Signed-off-by: Jeenu Viswambharan <jeenu.viswambharan@arm.com>

SDEI: Ensure SDEI handler executes with CVE-2018-3639 mitigation enabled ...

When dynamic mitigation is used, the SDEI handler is required to
execute with the mitigation enabled by default, regardless of the
mitigation state for lower ELs.  This means that if the kernel or
hypervisor explicitly disables the mitigation and then later when the
event is dispatched, the dispatcher will remember the mitigation state
for the lower ELs but force the mitigation to be on during the SDEI
handler execution.  When the SDEI handler returns, it will restore the
mitigation state.

This behaviour is described in "Firmware interfaces for mitigating
cache speculation vulnerabilities System Software on Arm Systems"[0].

[0] https://developer.arm.com/cache-speculation-vulnerability-firmware-specification

Change-Id: I8dd60b736be0aa9e832b0f92d67a401fdeb417f4
Signed-off-by: Dimitris Papastamos <dimitris.papastamos@arm.com>

SDEI: Pop dispatch context only after error checking ...

Currently, when the client attempts to do SDEI_EVENT_COMPLETE or
SDEI_EVENT_COMPLETE_AND_RESUME, the dispatcher pops off the outstanding
dispatch context for sanity check. There are however other checks
following this, which could potentially return failure. If that happens,
by popping the context, the dispatcher has inadvertently discarded a
valid context.

This patch fixes this bug by inspecting (not actually popping) the
outstanding context. The context is popped only after all error checks
are completed.

Change-Id: Ie199f6442f871a8177a8247a0c646543bad76d21
Signed-off-by: Jeenu Viswambharan <jeenu.viswambharan@arm.com>

SDEI: Fix security state check for explicit dispatch ...

Change-Id: Ic381ab5d03ec68c7f6e8d357ac2e2cbf0cc6b2e8
Signed-off-by: Jeenu Viswambharan <jeenu.viswambharan@arm.com>

SDEI: Add API for explicit dispatch ...

This allows for other EL3 components to schedule an SDEI event dispatch
to Normal world upon the next ERET. The API usage constrains are set out
in the SDEI dispatcher documentation.

Documentation to follow.

Change-Id: Id534bae0fd85afc94523490098c81f85c4e8f019
Signed-off-by: Jeenu Viswambharan <jeenu.viswambharan@arm.com>

BL31: Add SDEI dispatcher ...

The implementation currently supports only interrupt-based SDEI events,
and supports all interfaces as defined by SDEI specification version
1.0 [1].

Introduce the build option SDEI_SUPPORT to include SDEI dispatcher in
BL31.

Update user guide and porting guide. SDEI documentation to follow.

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

Change-Id: I758b733084e4ea3b27ac77d0259705565842241a
Co-authored-by: Yousuf A <yousuf.sait@arm.com>
Signed-off-by: Jeenu Viswambharan <jeenu.viswambharan@arm.com>