Julius Werner [Wed, 10 Jan 2018 23:12:47 +0000 (15:12 -0800)]
Makefile: Use ld.bfd linker if available
Some toolchain distributions install both the BFD and GOLD linkers under
the names <target>-ld.bfd and <target>-ld.gold. <target>-ld will then be
a symlink that may point to either one of these.
Trusted Firmware should always be linked with the BFD linker, since GOLD
is meant primarily for userspace programs and doesn't support many of
the more obscure linker script features that may be needed for firmware.
With this patch the Makefile will auto-detect if ld.bfd is available and
use it explicitly in that case.
Change-Id: I7017055f67db3bd57d191d20a7af06ca646937d7 Signed-off-by: Julius Werner <jwerner@chromium.org>
This patch maps the devices in the first GB of the system address map
on the FVP into the S-EL1&0 translation regime when SPM support is
enabled. This grants the Secure Partition access to the devices in
this region, for example the memory-mapped Generic Timer device.
Andreas Färber [Sat, 27 Jan 2018 15:46:59 +0000 (16:46 +0100)]
fiptool: Fix use after free
Commit 880b9e8b4c99ad99eee14079d5a6162733ef4931 (Add padding at the end
of the last entry) added code using toc_entry pointer, whose memory is
already freed via variable buf. This causes enormous padding on openSUSE.
Free the memory buffer only after padding is done.
Victor Chong [Sat, 27 Jan 2018 12:36:12 +0000 (21:36 +0900)]
hikey: fix assert in sec_protect()
`assert(e)` was used in place of `if (e) ERROR()` when sec_protect()
was ported from hikey fork so the logic should have been reversed.
Fixes: 3d5d9f5a ("hikey: configure the top 16MB of DRAM as secure") Fixes: 52988b38 ("hikey: configure 4 MB of secure DRAM for OP-TEE
Secure Data Path") Signed-off-by: Victor Chong <victor.chong@linaro.org> Tested-by: Victor Chong <victor.chong@linaro.org>
Julius Werner [Mon, 22 Jan 2018 22:02:03 +0000 (14:02 -0800)]
delay_timer: Guarantee that delay time can never be undershot
Delay functions like udelay() are often used to ensure that the
necessary time passed to allow some asynchronous event to finish, such
as the stabilization delay for a power rail. For these use cases it is
not very problematic if the delay is slightly longer than requested,
but it is critical that the delay must never be shorter.
The current udelay() implementation contains two hazards that may cause
the delay to be slightly shorter than intended: Firstly, the amount of
ticks to wait is calculated with an integer division, which may cut off
the last fraction of ticks needed. Secondly, the delay may be short by a
fraction of a tick because we do not know whether the initial ("start")
sample of the timer was near the start or near the end of the current
tick. Thus, if the code intends to wait for one tick, it might read the
timer value close to the end of the current tick and then read it again
right after the start of the next tick, concluding that the duration of
a full tick has passed when it in fact was just a fraction of it.
This patch rounds up the division and always adds one extra tick to
counteract both problems and ensure that delays will always be larger
but never smaller than requested.
Change-Id: Ic5fe5f858b5cdf3c0dbf3e488d4d5702d9569433 Signed-off-by: Julius Werner <jwerner@chromium.org>
Masahiro Yamada [Tue, 19 Dec 2017 02:56:05 +0000 (11:56 +0900)]
uniphier: switch to BL2-AT-EL3 and remove BL1 support
UniPhier platform implements non-TF boot ROM. Prior to the BL2-AT-EL3
support, BL1 (worked as a pseudo ROM) was needed just for ensuring BL2
is entered at EL1-S. Now, this platform is able to avoid this waste.
Masahiro Yamada [Mon, 22 Jan 2018 09:35:16 +0000 (18:35 +0900)]
uniphier: set PROGRAMMABLE_RESET_ADDRESS to disable warm boot mailbox
The warm boot mailbox code is compiled if PROGRAMMABLE_RESET_ADDRESS
is disabled.
The warm boot mailbox is useless for UniPhier SoC family because BL1
is not the first image. The UniPhier platform implements non-TF ROM,
then BL1 works as a pseudo ROM, so it is never executed in the warm
boot.
The reset vector address is not actually programmable for UniPhier
platform, but it should not hurt to enable PROGRAMMABLE_RESET_ADDRESS
to disable the mailbox and remove pointless plat_get_my_entrypoint.
Peter Griffin [Thu, 21 Dec 2017 18:03:46 +0000 (18:03 +0000)]
hikey: configure 4 MB of secure DRAM for OP-TEE Secure Data Path
Update the memory firewall configuration to reserve 4 MB of secure RAM
for use by the kernel and OP-TEE as the Secure Data Path pool.
Note that this address range (0x3E800000 - 0x3EC00000) falls in the
range already set aside by UEFI (which reserves the upper 32 MB of the
1GB DRAM for OP-TEE [1]) and was previously unused.
[1] https://github.com/96boards-hikey/edk2/blob/hikey/HisiPkg/HiKeyPkg/Library/HiKeyLib/HiKeyMem.c#L44 Signed-off-by: Jerome Forissier <jerome.forissier@linaro.org> Signed-off-by: Peter Griffin <peter.griffin@linaro.org> Acked-by: Victor Chong <victor.chong@linaro.org>
Steve Capper [Tue, 23 Jan 2018 03:30:05 +0000 (03:30 +0000)]
Correct the Makefile logic for disabling PIE
In the Makefile we use findstring to locate gcc toolchains
that have PIE enabled by default.
Unfortunately the result of findstring is compared against
an integer, 1, rather than a non-empty string; the logic to
disable PIE then doesn't get applied.
This patch fixes the flag test.
Fixes: f7ec31db2db3 ("Disable PIE compilation option")
Change-Id: I4cd2866974e313d6b408f9681311d78a208ab468 Signed-off-by: Steve Capper <steve.capper@arm.com>
Julius Werner [Mon, 22 Jan 2018 21:56:13 +0000 (13:56 -0800)]
Make div_round_up() correct for divisors that are not a power of 2
The current div_round_up() implementation relies on round_up() which
only works correctly for boundaries that are a power of 2. It is
documented as such, but this still seems dangerously easy to overlook,
especially since many other environments (e.g. the Linux kernel) have a
similar macro without these limitations.
There is a different way to calculate this that can deal with all kinds
of divisors without other drawbacks, so let's just use that instead.
Change-Id: Id382736683f5d4e880ef00c53cfa23a2f9208440 Signed-off-by: Julius Werner <jwerner@chromium.org>
Sughosh Ganu [Mon, 11 Dec 2017 13:33:19 +0000 (19:03 +0530)]
SPM: Declare explicit width based types in secure_partition_boot_info_t structure
The secure_partition_boot_info_t structure is used to communicate boot
parameters with the StandaloneMM code executing at S-EL0 through a
shared buffer. Certain data types used for members of this structure
are opaque with their size depending on the toolchain being used.
Declare the members of the structure with explicit width based data
types, which would maintain compatibility across toolchains.
Soby Mathew [Fri, 10 Nov 2017 12:08:46 +0000 (12:08 +0000)]
Allow API deprecation for uniphier platform
The `override ERROR_DEPRECATION = 1` setting in uniphier platform
makes deprecation of API difficult. Hence removing the same. This
flag should be specified on the command line if needed.
Leo Yan [Mon, 22 Jan 2018 04:40:25 +0000 (12:40 +0800)]
Hikey960: Enable invalid FIQ handling
When some interrupts are configured as group 0 in GICv2, these
interrupts trigger FIQ signal; this results in the Linux kernel panic
by reporting log: "Bad mode in FIQ handler detected on CPU0, code
0x00000000 -- Unknown/Uncategorized". Unfortunately from kernel side it
has no permission to read the GIC register for group 0 interrupts so we
have no chance to get to know which interrupt is configured as secure
interrupt and cause the kernel panic.
For upper reason, this commit enables FIQ exception handling for
SPD_none case. If the system has not enabled SPD the FIQ interrupt is
trapped into EL3 and the FIQ handler can report the interrupt number so
we can easily narrow down which FIQ introduce unexpected interrupt.
After enable SPD we can rely on SPD interrupt route model to handle FIQ.
Julius Werner [Tue, 13 Jun 2017 22:53:45 +0000 (15:53 -0700)]
coreboot: Add support for CBMEM console
coreboot supports an in-memory console to store firmware logs even when
no serial console is available. It is widely supported by
coreboot-compatible bootloaders (including SeaBIOS and GRUB) and can be
read by the Linux kernel.
This patch allows BL31 to add its own log messages to this console. The
driver will be registered automatically if coreboot support is compiled
in and detects the presence of a console buffer in the coreboot tables.
Change-Id: I31254dfa0c2fdeb7454634134b5707b4b4154907 Signed-off-by: Julius Werner <jwerner@chromium.org>
Julius Werner [Wed, 2 Aug 2017 23:31:04 +0000 (16:31 -0700)]
rockchip: Move to MULTI_CONSOLE_API
This patch changes all Rockchip platforms to use the new
MULTI_CONSOLE_API. The platform-specific plat_crash_console
implementations are removed so that the platform can use the ones from
the common platform code instead.
Also change the registers used in plat_crash_print_regs. The existing
use of x16 and x17 has always been illegal, since those registers are
reserved for use by the linker as a temporary scratch registers in
intra-procedure-call veneers and can never be expected to maintain their
values across a function call.
Change-Id: I8249424150be8d5543ed4af93b56756795a5288f Signed-off-by: Julius Werner <jwerner@chromium.org>
Julius Werner [Fri, 9 Jun 2017 22:22:44 +0000 (15:22 -0700)]
rockchip: Use coreboot-supplied serial console on coreboot systems
This patch changes all Rockchip platforms to initialize the serial
console with information supplied by coreboot rather than hardcoded
base address and divisor values if BL31 is run on top of coreboot.
Moving the BL2-to-BL31 parameter parsing as early as possible to ensure
that the console is available for all following code.
Also update the Rockchip platform to use MULTI_CONSOLE_API.
Change-Id: I670d350fa2f8b8133539f91ac14977ab47db60d9 Signed-off-by: Julius Werner <jwerner@chromium.org>
Julius Werner [Fri, 9 Jun 2017 22:17:15 +0000 (15:17 -0700)]
Add platform-independent coreboot support library
This patch adds the foundation for a platform-independent coreboot
support library that can be shared by all platforms that boot BL31 from
coreboot (acting as BL2). It adds code to parse the "coreboot table", a
data structure that coreboot uses to communicate different kinds of
information to later-stage firmware and certain OS drivers.
As a first small use case for this information, allow platforms to
access the serial console configuration used by coreboot, removing the
need to hardcode base address and divisors and allowing Trusted Firmware
to benefit from coreboot's user configuration (e.g. which UART to pick
and which baud rate to use).
Change-Id: I2bfb39cd2609ce6640b844ab68df6c9ae3f28e9e Signed-off-by: Julius Werner <jwerner@chromium.org>
Julius Werner [Tue, 19 Sep 2017 00:01:06 +0000 (17:01 -0700)]
drivers: cadence: cdns: Update CDNS driver to support MULTI_CONSOLE_API
This patch updates the Cadence CDNS console driver to support the new
console API. The driver will continue to support the old API as well by
checking the MULTI_CONSOLE_API compile-time flag.
Change-Id: I2ef8fb0d6ab72696997db1e0243a533499569d6b Signed-off-by: Julius Werner <jwerner@chromium.org>
Julius Werner [Mon, 18 Sep 2017 23:59:43 +0000 (16:59 -0700)]
drivers: arm: pl011: Update PL011 driver to support MULTI_CONSOLE_API
This patch updates the ARM PL011 console driver to support the new
console API. The driver will continue to support the old API as well by
checking the MULTI_CONSOLE_API compile-time flag.
Change-Id: Ic34e4158addbb0c5fae500c9cff899c05a4f4206 Signed-off-by: Julius Werner <jwerner@chromium.org>
Julius Werner [Mon, 18 Sep 2017 23:57:51 +0000 (16:57 -0700)]
drivers: ti: uart: Update 16550 UART driver to support MULTI_CONSOLE_API
This patch updates the TI 16550 console driver to support the new
console API. The driver will continue to support the old API as well by
checking the MULTI_CONSOLE_API compile-time flag.
Change-Id: I60a44b7ba3c35c74561824c04b8dbe3e3039324c Signed-off-by: Julius Werner <jwerner@chromium.org>
Julius Werner [Mon, 18 Sep 2017 23:49:48 +0000 (16:49 -0700)]
Add default crash console code to hook up to new console API
This patch expands the weak stubs for the plat_crash_console_xxx
functions in common platform code to use the new console API for crash
output. This should make crash console output "just work" for most cases
without the need for the platform to explicitly set up a crash console.
For cases where the normal console framework doesn't work (e.g. very
early crashes, before the platform can register any consoles), platforms
are still able to override the functions just like before.
This feature requires the MULTI_CONSOLE_API compile-time flag to work.
For builds which don't have it set, this patch has no practical effect.
Change-Id: I80dd161cb43f9db59a0bad2dae33c6560cfac584 Signed-off-by: Julius Werner <jwerner@chromium.org>
Manoj Kumar [Fri, 19 Jan 2018 12:21:31 +0000 (17:51 +0530)]
lib/cpus: fix branching in reset function for cortex-a72 AARCH32 mode
In AARCH32 mode, cortex_a72_reset_func branches to address in lr
register instead of r5 register. This leads to linux boot failure
of Cortex-A72 cores in AARCH32 mode on Juno-R2 board.
This patch fixes the branching of cortex_a72_reset_func to r5
register as in cortex_a57_reset_func implementation.
Roberto Vargas [Tue, 16 Jan 2018 10:35:23 +0000 (10:35 +0000)]
bl2-el3: Don't compile BL1 when BL2_AT_EL3 is defined in FVP
This patch modifies the makefiles to avoid the definition
of BL1_SOURCES and BL2_SOURCES in the tbbr makefiles, and
it lets to the platform makefiles to define them if they
actually need these images. In the case of BL2_AT_EL3
BL1 will not be needed usually because the Boot ROM will
jump directly to BL2.
Roberto Vargas [Tue, 2 Jan 2018 11:23:41 +0000 (11:23 +0000)]
bl2-el3: Don't include BL2 in fip for BL2 at EL3
It is better to not include BL2 in FIP when using `BL2 at EL3` as
platforms using this config would not have the capability to parse the
FIP format in Boot ROM and BL2 needs to be loaded independently. This
patch does the required changes for the same.
Roberto Vargas [Mon, 20 Nov 2017 13:36:10 +0000 (13:36 +0000)]
bl2-el3: Add documentation for BL2 at EL3
Update firmware-design.rst, porting-guide.rst and user-guide.rst
with the information about BL2 at EL3. Firmware-design.rst is
also update to explain how to test this feauture with FVP.
Workaround for CVE-2017-5715 for Cortex A9, A15 and A17
A per-cpu vbar is installed that implements the workaround by
invalidating the branch target buffer (BTB) directly in the case of A9
and A17 and indirectly by invalidating the icache in the case of A15.
For Cortex A57 and A72 there is currently no workaround implemented
when EL3 is in AArch32 mode so report it as missing.
For other vulnerable CPUs (e.g. Cortex A73 and Cortex A75), there are
no changes since there is currently no upstream AArch32 EL3 support
for these CPUs.
This patch introduces two workarounds for ARMv7 systems. The
workarounds need to be applied prior to any `branch` instruction in
secure world. This is achieved using a custom vector table where each
entry is an `add sp, sp, #1` instruction.
On entry to monitor mode, once the sequence of `ADD` instructions is
executed, the branch target buffer (BTB) is invalidated. The bottom
bits of `SP` are then used to decode the exception entry type.
A side effect of this change is that the exception vectors are
installed before the CPU specific reset function. This is now
consistent with how it is done on AArch64.
Note, on AArch32 systems, the exception vectors are typically tightly
integrated with the secure payload (e.g. the Trusted OS). This
workaround will need porting to each secure payload that requires it.
The patch to modify the AArch32 per-cpu vbar to the corresponding
workaround vector table according to the CPU type will be done in a
later patch.
Print erratum application report for CVE-2017-5715
Even though the workaround for CVE-2017-5715 is not a CPU erratum, the
code is piggybacking on the errata framework to print whether the
workaround was applied, missing or not needed.
Roberto Vargas [Fri, 17 Nov 2017 10:51:54 +0000 (10:51 +0000)]
bl2-el3: Mark all the assembly functions in bl2 at el3
When BL2_AT_EL3 option is enabled some platforms are going to
need a resident part in BL2 because the boot rom may jump to it
after a reset. This patch introduces __TEXT_RESIDENT_START__ and
__TEXT_RESIDENT_END__ linker symbols that mark the resident region.
Roberto Vargas [Thu, 2 Nov 2017 16:36:51 +0000 (16:36 +0000)]
Mark functions defined in assembly files
This patch change the name of the section containing the functions
defined in assembly files from text.* to text.asm.*. This change
makes possible to select in the linker script the functions
defined in those files.
Roberto Vargas [Fri, 17 Nov 2017 13:22:18 +0000 (13:22 +0000)]
bl2-el3: Add BL2 at EL3 support in FVP
This patch add supports for the new API added for BL2 at EL3 for
FVP. We don't have a non-TF Boot ROM for FVP, but this option can be
tested setting specific parameters in the model.
The bl2 image is loaded directly in memory instead of being loaded
by a non-TF Boot ROM and the reset address is changed:
These parameters mean that in the cold boot path the processor will
jump to BL2 again. For this reason, BL2 is loaded in dram in this
case, to avoid other images reclaiming BL2 memory.
Roberto Vargas [Mon, 30 Oct 2017 14:43:43 +0000 (14:43 +0000)]
bl2-el3: Add BL2_EL3 image
This patch enables BL2 to execute at the highest exception level
without any dependancy on TF BL1. This enables platforms which already
have a non-TF Boot ROM to directly load and execute BL2 and subsequent BL
stages without need for BL1. This is not currently possible because
BL2 executes at S-EL1 and cannot jump straight to EL3.
Leo Yan [Thu, 4 Jan 2018 01:32:50 +0000 (09:32 +0800)]
Hikey960: Change CPU standby state for WFI
At early time, the CPU CA73 retention state has been supported on
Hikey960. Later we found the system has the hang issue and for
resolving this issue Hisilicon released new MCU firmware, but
unfortunately the new MCU firmware has side effect and results in the
CA73 CPU cannot really enter retention state and roll back to WFI state.
After discussion we cannot see the possibility to enable CA73 retention
state anymore on Hikey960, based on this conclusion we should remove
this state supporting from ARM-TF and roll back to WFI state only. We
will commit one patch to remove CA73 CPU retention state in kernel DT
binding as well.
Cc: Daniel Lezcano <daniel.lezcano@linaro.org> Cc: Haojian Zhuang <haojian.zhuang@linaro.org> Cc: Kevin Wang <jean.wangtao@linaro.org> Cc: Vincent Guittot <vincent.guittot@linaro.org> Signed-off-by: Leo Yan <leo.yan@linaro.org>
The commit fdae60b6ba27c216fd86d13b7432a1ff4f57dd84 changed the
parameter encoding for the hikey960. However that implies a DT change
in the kernel side. After submitting the DT change for upstreaming,
the backward compatibility issue and the interface change raise some
concerns from the Linux community about the issues related to kernel <->
ATF alignment. There is no way to detect a mis-alignment of those
without a deep knowledge of the ATF and the kernel. Furthermore, the
failing calls to PSCI in the idle path (because of bad parameters), will
lead to busy looping, implying: thermal issues and extra energy
consumption.
In regard of the Linux community concerns, the potential issues when the
ATF and the kernel are not aligned, it is preferable to revert the
commit.
Cc: Vincent Guittot <vincent.guittot@linaro.org> Cc: Haojian Zhuang <haojian.zhuang@linaro.org> Cc: Kevin Wang <jean.wangtao@linaro.org> Co-authored-by: Daniel Lezcano <daniel.lezcano@linaro.org> Signed-off-by: Leo Yan <leo.yan@linaro.org>
If AMU is not supported by the hardware but it is enabled in Trusted
Firmware, the console will be spammed with warnings every time a CPU
is brought up with a CPU ON call.
Remove the warning message as this is more in line with how other
extensions like SPE and SVE are handled.
On some systems, the AMU counters might reset to 0 when a CPU
powerdown happens. This behaviour conflicts with the intended
use-case of AMU as lower ELs are only expected to see non-decreasing
counter values.
Add some AMU helper functions to allow configuring, reading and
writing of the Group 0 and Group 1 counters. Documentation for these
helpers will come in a separate patch.
AMU: Add plat interface to select which group 1 counters to enable
A new platform macro `PLAT_AMU_GROUP1_COUNTERS_MASK` controls which
group 1 counters should be enabled. The maximum number of group 1
counters supported by AMUv1 is 16 so the mask can be at most 0xffff.
If the platform does not define this mask, no group 1 counters are
enabled.
A related platform macro `PLAT_AMU_GROUP1_NR_COUNTERS` is used by
generic code to allocate an array to save and restore the counters on
CPU suspend.
Use PFR0 to identify need for mitigation of CVE-2017-5915
If the CSV2 field reads as 1 then branch targets trained in one
context cannot affect speculative execution in a different context.
In that case skip the workaround on Cortex A75.
Workaround for CVE-2017-5715 on Cortex A73 and A75
Invalidate the Branch Target Buffer (BTB) on entry to EL3 by
temporarily dropping into AArch32 Secure-EL1 and executing the
`BPIALL` instruction.
This is achieved by using 3 vector tables. There is the runtime
vector table which is used to handle exceptions and 2 additional
tables which are required to implement this workaround. The
additional tables are `vbar0` and `vbar1`.
The sequence of events for handling a single exception is
as follows:
1) Install vector table `vbar0` which saves the CPU context on entry
to EL3 and sets up the Secure-EL1 context to execute in AArch32 mode
with the MMU disabled and I$ enabled. This is the default vector table.
2) Before doing an ERET into Secure-EL1, switch vbar to point to
another vector table `vbar1`. This is required to restore EL3 state
when returning from the workaround, before proceeding with normal EL3
exception handling.
3) While in Secure-EL1, the `BPIALL` instruction is executed and an
SMC call back to EL3 is performed.
4) On entry to EL3 from Secure-EL1, the saved context from step 1) is
restored. The vbar is switched to point to `vbar0` in preparation to
handle further exceptions. Finally a branch to the runtime vector
table entry is taken to complete the handling of the original
exception.
This workaround is enabled by default on the affected CPUs.
NOTE
====
There are 4 different stubs in Secure-EL1. Each stub corresponds to
an exception type such as Sync/IRQ/FIQ/SError. Each stub will move a
different value in `R0` before doing an SMC call back into EL3.
Without this piece of information it would not be possible to know
what the original exception type was as we cannot use `ESR_EL3` to
distinguish between IRQs and FIQs.
Workaround for CVE-2017-5715 on Cortex A57 and A72
Invalidate the Branch Target Buffer (BTB) on entry to EL3 by disabling
and enabling the MMU. To achieve this without performing any branch
instruction, a per-cpu vbar is installed which executes the workaround
and then branches off to the corresponding vector entry in the main
vector table. A side effect of this change is that the main vbar is
configured before any reset handling. This is to allow the per-cpu
reset function to override the vbar setting.
This workaround is enabled by default on the affected CPUs.
`mm_cursor` doesn't have the needed data because the `memmove()` that
is called right before it overwrites that information. In order to get
the information of the region that was being mapped, `mm` has to be used
instead (like it is done to fill the fields of `unmap_mm`).
If the incorrect information is read, this check isn't reliable and
`xlat_tables_unmap_region` may be requested to unmap memory that isn't
mapped at all, triggering assertions.
Change-Id: I602d4ac83095d4e5dac9deb34aa5d00d00e6c289 Signed-off-by: Antonio Nino Diaz <antonio.ninodiaz@arm.com>
Roberto Vargas [Tue, 12 Dec 2017 10:39:44 +0000 (10:39 +0000)]
Add documentation about plat_try_next_boot_source to bl1_platform_setup
If boot redundancy is required in BL1 then the initialization
of the boot sequence must be done in bl1_platform_setup. In BL2,
we had to add a new function, bl2_preload_setup, because
bl2_platform_setup is called after the images are loaded, making it
invalid for the boot sequence initialization.
Wendy Liang [Wed, 4 Oct 2017 06:21:11 +0000 (23:21 -0700)]
zynqmp: pm_service: use zynqmp_ipi APIs
Use zynqmp_ipi APIs to access IPI registers in pm_service.
As the zynqmp_ipi APIs doesn't cover IPI buffers, the pm_ipi
in pm_service will still directly access the IPI buffers.
Previously, ZynqMP IPI in ATF is only for ZynqMP PM,
This patch is to have a ZynqMP IPI implementation to handle
both ZynqMP PM IPI requirement and IPI mailbox service requirement
which will be introduced next.
We control IPI agents registers access but not IPI buffers access in
this implementation. Each IPI mailbox user will directly access the
IPI buffers.