__early_cpu_boot_status is of type long. Use quad
assembler directive to allocate proper size.
Acked-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Arun KS <arunks@codeaurora.org>
Signed-off-by: Will Deacon <will.deacon@arm.com>

As of commit ece0e2b6 ("mm: remove pte_*map_nested()"),
pte_unmap_nested() is no longer used and can be removed from the arm64
code.
Signed-off-by: Qian Cai <cai@lca.pw>
[will: also remove pte_offset_map_nested()]
Signed-off-by: Will Deacon <will.deacon@arm.com>

When building with -Wunused-but-set-variable, the compiler shouts about
a number of pte_unmap() users, since this expands to an empty macro on
arm64:

  | mm/gup.c: In function 'gup_pte_range':
  | mm/gup.c:1727:16: warning: variable 'ptem' set but not used
  | [-Wunused-but-set-variable]
  | mm/gup.c: At top level:
  | mm/memory.c: In function 'copy_pte_range':
  | mm/memory.c:821:24: warning: variable 'orig_dst_pte' set but not used
  | [-Wunused-but-set-variable]
  | mm/memory.c:821:9: warning: variable 'orig_src_pte' set but not used
  | [-Wunused-but-set-variable]
  | mm/swap_state.c: In function 'swap_ra_info':
  | mm/swap_state.c:641:15: warning: variable 'orig_pte' set but not used
  | [-Wunused-but-set-variable]
  | mm/madvise.c: In function 'madvise_free_pte_range':
  | mm/madvise.c:318:9: warning: variable 'orig_pte' set but not used
  | [-Wunused-but-set-variable]

Rewrite pte_unmap() as a static inline function, which silences the
warnings.
Signed-off-by: Qian Cai <cai@lca.pw>
Signed-off-by: Will Deacon <will.deacon@arm.com>

With the introduction of the config option that allows to enable kuser
helpers, it is now possible to reduce TASK_SIZE_32 when these are
disabled and 64K pages are enabled. This extends the compliance with
the section 6.5.8 of the C standard (C99).
Acked-by: Catalin Marinas <catalin.marinas@arm.com>
Reported-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Vincenzo Frascino <vincenzo.frascino@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>

When executing clock_gettime(), either in the vDSO or via a system call,
we need to ensure that the read of the counter register occurs within
the seqlock reader critical section. This ensures that updates to the
clocksource parameters (e.g. the multiplier) are consistent with the
counter value and therefore avoids the situation where time appears to
go backwards across multiple reads.

Extend the vDSO logic so that the seqlock critical section covers the
read of the counter register as well as accesses to the data page. Since
reads of the counter system registers are not ordered by memory barrier
instructions, introduce dependency ordering from the counter read to a
subsequent memory access so that the seqlock memory barriers apply to
the counter access in both the vDSO and the system call paths.

Cc: <stable@vger.kernel.org>
Cc: Marc Zyngier <marc.zyngier@arm.com>
Tested-by: Vincenzo Frascino <vincenzo.frascino@arm.com>
Link: https://lore.kernel.org/linux-arm-kernel/alpine.DEB.2.21.1902081950260.1662@nanos.tec.linutronix.de/Reported-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Will Deacon <will.deacon@arm.com>

Functions called in '_sdei_handler' are needed to be marked as
'nokprobe'. Because these functions are called in NMI context and
neither the arch-code's debug infrastructure nor kprobes core supports
this.
Signed-off-by: Xiongfeng Wang <wangxiongfeng2@huawei.com>
Reviewed-by: James Morse <james.morse@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>

The file offset argument to the arm64 sys_mmap() implementation is
scaled from bytes to pages by shifting right by PAGE_SHIFT.
Unfortunately, the offset is passed in as a signed 'off_t' type and
therefore large offsets (i.e. with the top bit set) are incorrectly
sign-extended by the shift. This has been observed to cause false mmap()
failures when mapping GPU doorbells on an arm64 server part.

Change the type of the file offset argument to sys_mmap() from 'off_t'
to 'unsigned long' so that the shifting scales the value as expected.

Cc: <stable@vger.kernel.org>
Signed-off-by: Boyang Zhou <zhouby_cn@126.com>
[will: rewrote commit message]
Signed-off-by: Will Deacon <will.deacon@arm.com>

The nature of silicon errata means that the Kconfig help text for our
various software workarounds has been written by many different people.
Along the way, we've accumulated typos and inconsistencies which make
the options needlessly difficult to read.

Fix up minor issues with the help text.
Signed-off-by: Will Deacon <will.deacon@arm.com>

Clang's integrated assembler does not allow assembly macros defined
in one inline asm block using the .macro directive to be used across
separate asm blocks. LLVM developers consider this a feature and not a
bug, recommending code refactoring:

  https://bugs.llvm.org/show_bug.cgi?id=19749

As binutils doesn't allow macros to be redefined, this change uses
UNDEFINE_MRS_S and UNDEFINE_MSR_S to define corresponding macros
in-place and workaround gcc and clang limitations on redefining macros
across different assembler blocks.

Specifically, the current state after preprocessing looks like this:

asm volatile(".macro mXX_s ... .endm");
void f()
{
	asm volatile("mXX_s a, b");
}

With GCC, it gives macro redefinition error because sysreg.h is included
in multiple source files, and assembler code for all of them is later
combined for LTO (I've seen an intermediate file with hundreds of
identical definitions).

With clang, it gives macro undefined error because clang doesn't allow
sharing macros between inline asm statements.

I also seem to remember catching another sort of undefined error with
GCC due to reordering of macro definition asm statement and generated
asm code for function that uses the macro.

The solution with defining and undefining for each use, while certainly
not elegant, satisfies both GCC and clang, LTO and non-LTO.
Co-developed-by: Alex Matveev <alxmtvv@gmail.com>
Co-developed-by: Yury Norov <ynorov@caviumnetworks.com>
Co-developed-by: Sami Tolvanen <samitolvanen@google.com>
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
Reviewed-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Will Deacon <will.deacon@arm.com>

This patch provides support for reporting the presence of SVE2 and
its optional features to userspace.

This will also enable visibility of SVE2 for guests, when KVM
support for SVE-enabled guests is available.
Signed-off-by: Dave Martin <Dave.Martin@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>

Make CONFIG_COMPAT a menuconfig entry so that we can place
CONFIG_KUSER_HELPERS and CONFIG_ARMV8_DEPRECATED underneath it.
Signed-off-by: Will Deacon <will.deacon@arm.com>

When kuser helpers are enabled the kernel maps the relative code at
a fixed address (0xffff0000). Making configurable the option to disable
them means that the kernel can remove this mapping and any access to
this memory area results in a sigfault.

Add a KUSER_HELPERS config option that can be used to disable the
mapping when it is turned off.

This option can be turned off if and only if the applications are
designed specifically for the platform and they do not make use of the
kuser helpers code.

Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will.deacon@arm.com>
Signed-off-by: Vincenzo Frascino <vincenzo.frascino@arm.com>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
[will: Use IS_ENABLED() instead of #ifdef]
Signed-off-by: Will Deacon <will.deacon@arm.com>

aarch32_alloc_vdso_pages() needs to be refactored to make it
easier to disable kuser helpers.

Divide the function in aarch32_alloc_kuser_vdso_page() and
aarch32_alloc_sigreturn_vdso_page().

Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will.deacon@arm.com>
Signed-off-by: Vincenzo Frascino <vincenzo.frascino@arm.com>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
[will: Inlined sigpage allocation to simplify error paths]
Signed-off-by: Will Deacon <will.deacon@arm.com>

To make it possible to disable kuser helpers in aarch32 we need to
divide the kuser and the sigreturn functionalities.

Split the current version of kuser32 in kuser32 (for kuser helpers)
and sigreturn32 (for sigreturn helpers).

Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will.deacon@arm.com>
Signed-off-by: Vincenzo Frascino <vincenzo.frascino@arm.com>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>

For AArch32 tasks, we install a special "[vectors]" page that contains
the sigreturn trampolines and kuser helpers, which is mapped at a fixed
address specified by the kuser helpers ABI.

Having the sigreturn trampolines in the same page as the kuser helpers
makes it impossible to disable the kuser helpers independently.

Follow the Arm implementation, by moving the signal trampolines out of
the "[vectors]" page and into their own "[sigpage]".

Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will.deacon@arm.com>
Signed-off-by: Vincenzo Frascino <vincenzo.frascino@arm.com>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
[will: tweaked comments and fixed sparse warning]
Signed-off-by: Will Deacon <will.deacon@arm.com>

In a system where, through IORT firmware mappings, the SMMU device is
mapped to a NUMA node that is not online, the kernel bootstrap results
in the following crash:

  Unable to handle kernel paging request at virtual address 0000000000001388
  Mem abort info:
    ESR = 0x96000004
    Exception class = DABT (current EL), IL = 32 bits
    SET = 0, FnV = 0
    EA = 0, S1PTW = 0
  Data abort info:
    ISV = 0, ISS = 0x00000004
    CM = 0, WnR = 0
  [0000000000001388] user address but active_mm is swapper
  Internal error: Oops: 96000004 [#1] SMP
  Modules linked in:
  CPU: 5 PID: 1 Comm: swapper/0 Not tainted 5.0.0 #15
  pstate: 80c00009 (Nzcv daif +PAN +UAO)
  pc : __alloc_pages_nodemask+0x13c/0x1068
  lr : __alloc_pages_nodemask+0xdc/0x1068
  ...
  Process swapper/0 (pid: 1, stack limit = 0x(____ptrval____))
  Call trace:
   __alloc_pages_nodemask+0x13c/0x1068
   new_slab+0xec/0x570
   ___slab_alloc+0x3e0/0x4f8
   __slab_alloc+0x60/0x80
   __kmalloc_node_track_caller+0x10c/0x478
   devm_kmalloc+0x44/0xb0
   pinctrl_bind_pins+0x4c/0x188
   really_probe+0x78/0x2b8
   driver_probe_device+0x64/0x110
   device_driver_attach+0x74/0x98
   __driver_attach+0x9c/0xe8
   bus_for_each_dev+0x84/0xd8
   driver_attach+0x30/0x40
   bus_add_driver+0x170/0x218
   driver_register+0x64/0x118
   __platform_driver_register+0x54/0x60
   arm_smmu_driver_init+0x24/0x2c
   do_one_initcall+0xbc/0x328
   kernel_init_freeable+0x304/0x3ac
   kernel_init+0x18/0x110
   ret_from_fork+0x10/0x1c
  Code: f90013b5 b9410fa1 1a9f0694 b50014c2 (b9400804)
  ---[ end trace dfeaed4c373a32da ]--

Change the dev_set_proximity() hook prototype so that it returns a
value and make it return failure if the PXM->NUMA-node mapping
corresponds to an offline node, fixing the crash.
Acked-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Signed-off-by: Kefeng Wang <wangkefeng.wang@huawei.com>
Link: https://lore.kernel.org/linux-arm-kernel/20190315021940.86905-1-wangkefeng.wang@huawei.com/Signed-off-by: Will Deacon <will.deacon@arm.com>

clock_getres() in the vDSO library has to preserve the same behaviour
of posix_get_hrtimer_res().

In particular, posix_get_hrtimer_res() does:

    sec = 0;
    ns = hrtimer_resolution;

where 'hrtimer_resolution' depends on whether or not high resolution
timers are enabled, which is a runtime decision.

The vDSO incorrectly returns the constant CLOCK_REALTIME_RES. Fix this
by exposing 'hrtimer_resolution' in the vDSO datapage and returning that
instead.
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Vincenzo Frascino <vincenzo.frascino@arm.com>
[will: Use WRITE_ONCE(), move adr off COARSE path, renumber labels, use 'w' reg]
Signed-off-by: Will Deacon <will.deacon@arm.com>

This patch corrects the SPDX License Identifier style
in the arm64 Hardware Architecture related files.
Suggested-by: Joe Perches <joe@perches.com>
Signed-off-by: Nishad Kamdar <nishadkamdar@gmail.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>

Our __smp_store_release() and __smp_load_acquire() macros use inline
assembly, which is opaque to kasan. This means that kasan can't catch
erroneous use of these.

This patch adds kasan instrumentation to both.

Cc: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Mark Rutland <mark.rutland@arm.com>
[will: consistently use *p as argument to sizeof]
Signed-off-by: Will Deacon <will.deacon@arm.com>

This change uses the original virt_to_page() (the one with __pa()) to
check the given virtual address if CONFIG_DEBUG_VIRTUAL=y.

Recently, I worked on a bug: a driver passes a symbol address to
dma_map_single() and the virt_to_page() (called by dma_map_single())
does not work for non-linear addresses after commit 9f287591
("arm64: mm: restrict virt_to_page() to the linear mapping").

I tried to trap the bug by enabling CONFIG_DEBUG_VIRTUAL but it
did not work - bacause the commit removes the __pa() from
virt_to_page() but CONFIG_DEBUG_VIRTUAL checks the virtual address
in __pa()/__virt_to_phys().

A simple solution is to use the original virt_to_page()
(the one with__pa()) if CONFIG_DEBUG_VIRTUAL=y.

Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Acked-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Miles Chen <miles.chen@mediatek.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>

Advertise ARM64_HAS_DCPODP when both DC CVAP and DC CVADP are supported.

Even though we don't use this feature now, we provide it for consistency
with DCPOP and anticipate it being used in the future.
Signed-off-by: Andrew Murray <andrew.murray@arm.com>
Reviewed-by: Dave Martin <Dave.Martin@arm.com>
Reviewed-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>

Allow users of dcache_by_line_op to specify cvadp as an op.
Signed-off-by: Andrew Murray <andrew.murray@arm.com>
Reviewed-by: Dave Martin <Dave.Martin@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>

ARMv8.5 builds upon the ARMv8.2 DC CVAP instruction by introducing a DC
CVADP instruction which cleans the data cache to the point of deep
persistence. Let's expose this support via the arm64 ELF hwcaps.
Signed-off-by: Andrew Murray <andrew.murray@arm.com>
Reviewed-by: Dave Martin <Dave.Martin@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>

The ARMv8.5 DC CVADP instruction may be trapped to EL1 via
SCTLR_EL1.UCI therefore let's provide a handler for it.

Just like the CVAP instruction we use a 'sys' instruction instead of
the 'dc' alias to avoid build issues with older toolchains.
Signed-off-by: Andrew Murray <andrew.murray@arm.com>
Reviewed-by: Mark Rutland <mark.rutland@arm.com>
Reviewed-by: Dave Martin <Dave.Martin@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>

The introduction of AT_HWCAP2 introduced accessors which ensure that
hwcap features are set and tested appropriately.

Let's now mandate access to elf_hwcap via these accessors by making
elf_hwcap static within cpufeature.c.
Signed-off-by: Andrew Murray <andrew.murray@arm.com>
Reviewed-by: Dave Martin <Dave.Martin@arm.com>
Reviewed-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>

As we will exhaust the first 32 bits of AT_HWCAP let's start
exposing AT_HWCAP2 to userspace to give us up to 64 caps.

Whilst it's possible to use the remaining 32 bits of AT_HWCAP, we
prefer to expand into AT_HWCAP2 in order to provide a consistent
view to userspace between ILP32 and LP64. However internal to the
kernel we prefer to continue to use the full space of elf_hwcap.

To reduce complexity and allow for future expansion, we now
represent hwcaps in the kernel as ordinals and use a
KERNEL_HWCAP_ prefix. This allows us to support automatic feature
based module loading for all our hwcaps.

We introduce cpu_set_feature to set hwcaps which complements the
existing cpu_have_feature helper. These helpers allow us to clean
up existing direct uses of elf_hwcap and reduce any future effort
required to move beyond 64 caps.

For convenience we also introduce cpu_{have,set}_named_feature which
makes use of the cpu_feature macro to allow providing a hwcap name
without a {KERNEL_}HWCAP_ prefix.
Signed-off-by: Andrew Murray <andrew.murray@arm.com>
[will: use const_ilog2() and tweak documentation]
Signed-off-by: Will Deacon <will.deacon@arm.com>

Add regs_get_argument() which returns N th argument of the function
call. On arm64, it supports up to 8th argument.
Note that this chooses most probably assignment, in some case
it can be incorrect (e.g. passing data structure or floating
point etc.)

This enables ftrace kprobe events to access kernel function
arguments via $argN syntax.
Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
[will: tidied up the comment a bit]
Signed-off-by: Will Deacon <will.deacon@arm.com>

We use $(LD) to link vmlinux, modules, decompressors, etc.

VDSO is the only exceptional case where $(CC) is used as the linker
driver, but I do not know why we need to do so. VDSO uses a special
linker script, and does not link standard libraries at all.

I changed the Makefile to use $(LD) rather than $(CC). I tested this,
and VDSO worked for me.

Users will be able to use their favorite linker (e.g. lld instead of
of bfd) by passing LD= from the command line.

My plan is to rewrite all VDSO Makefiles to use $(LD), then delete
cc-ldoption.
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>

Currently, compat tasks running on arm64 can allocate memory up to
TASK_SIZE_32 (UL(0x100000000)).

This means that mmap() allocations, if we treat them as returning an
array, are not compliant with the sections 6.5.8 of the C standard
(C99) which states that: "If the expression P points to an element of
an array object and the expression Q points to the last element of the
same array object, the pointer expression Q+1 compares greater than P".

Redefine TASK_SIZE_32 to address the issue.

Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will.deacon@arm.com>
Cc: Jann Horn <jannh@google.com>
Cc: <stable@vger.kernel.org>
Reported-by: Jann Horn <jannh@google.com>
Signed-off-by: Vincenzo Frascino <vincenzo.frascino@arm.com>
[will: fixed typo in comment]
Signed-off-by: Will Deacon <will.deacon@arm.com>

When the CPU comes out of suspend, the firmware may have modified the OS
Double Lock Register. Save it in an unused slot of cpu_suspend_ctx, and
restore it on resume.

Cc: <stable@vger.kernel.org>
Signed-off-by: Jean-Philippe Brucker <jean-philippe.brucker@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>

Some firmwares may reboot CPUs with OS Double Lock set. Make sure that
it is unlocked, in order to use debug exceptions.

Cc: <stable@vger.kernel.org>
Signed-off-by: Jean-Philippe Brucker <jean-philippe.brucker@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>

The logic for early allocation of page tables is duplicated between
pgd_kernel_pgtable_alloc() and pgd_pgtable_alloc(). Drop the duplication
by calling one from the other and renaming pgd_kernel_pgtable_alloc()
accordingly.
Signed-off-by: Will Deacon <will.deacon@arm.com>

Switch from per mm_struct to per pmd page table lock by enabling
ARCH_ENABLE_SPLIT_PMD_PTLOCK. This provides better granularity for
large system.

I'm not sure if there is contention on mm->page_table_lock. Given
the option comes at no cost (apart from initializing more spin
locks), why not enable it now.

We only do so when pmd is not folded, so we don't mistakenly call
pgtable_pmd_page_ctor() on pud or p4d in pgd_pgtable_alloc().
Signed-off-by: Yu Zhao <yuzhao@google.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>

ARM64 standard pgtable functions are going to use pgtable_page_[ctor|dtor]
or pgtable_pmd_page_[ctor|dtor] constructs. At present KVM guest stage-2
PUD|PMD|PTE level page tabe pages are allocated with __get_free_page()
via mmu_memory_cache_alloc() but released with standard pud|pmd_free() or
pte_free_kernel(). These will fail once they start calling into pgtable_
[pmd]_page_dtor() for pages which never originally went through respective
constructor functions. Hence convert all stage-2 page table page release
functions to call buddy directly while freeing pages.
Reviewed-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Acked-by: Yu Zhao <yuzhao@google.com>
Acked-by: Marc Zyngier <marc.zyngier@arm.com>
Signed-off-by: Anshuman Khandual <anshuman.khandual@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>

init_mm doesn't require page table lock to be initialized at
any level. Add a separate page table allocator for it, and the
new one skips page table ctors.

The ctors allocate memory when ALLOC_SPLIT_PTLOCKS is set. Not
calling them avoids memory leak in case we call pte_free_kernel()
on init_mm.
Acked-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Yu Zhao <yuzhao@google.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>

For pte page, use pgtable_page_ctor(); for pmd page, use
pgtable_pmd_page_ctor(); and for the rest (pud, p4d and pgd),
don't use any.

For now, we don't select ARCH_ENABLE_SPLIT_PMD_PTLOCK and
pgtable_pmd_page_ctor() is a nop. When we do in patch 3, we
make sure pmd is not folded so we won't mistakenly call
pgtable_pmd_page_ctor() on pud or p4d.
Acked-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Yu Zhao <yuzhao@google.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>

brk_handler() now looks pretty strange and can be refactored to drop its
funny 'handler_found' local variable altogether.
Reviewed-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>

kprobes and uprobes reserve some BRK immediates for installing their
probes. Define these along with the other reservations in brk-imm.h
and rename the ESR definitions to be consistent with the others that we
already have.
Reviewed-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>

Now that the debug hook dispatching code takes the triggering exception
level into account, there's no need for the hooks themselves to poke
around with user_mode(regs).
Reviewed-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>

Kprobes bypasses our debug hook registration code so that it doesn't
get tangled up with recursive debug exceptions from things like lockdep:

  http://lists.infradead.org/pipermail/linux-arm-kernel/2015-February/324385.html

However, since then, (a) the hook list has become RCU protected and (b)
the kprobes hooks were found not to filter out exceptions from userspace
correctly. On top of that, the step handler is invoked directly from
single_step_handler(), which *does* use the debug hook list, so it's
clearly not the end of the world.

For now, have kprobes use the debug hook registration API like everybody
else. We can revisit this in the future if this is found to limit
coverage significantly.
Reviewed-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>