diff options
| author | Ard Biesheuvel <ard.biesheuvel@linaro.org> | 2017-07-20 17:15:45 +0100 |
|---|---|---|
| committer | Mark Rutland <mark.rutland@arm.com> | 2017-08-15 18:34:53 +0100 |
| commit | 34be98f4944f99076f049a6806fc5f5207a755d3 (patch) | |
| tree | f7d3b12acec57f6b11d2384f299fb747a482f155 /arch/arm64/kernel | |
| parent | 48ac3c18cc62d4a23d5dc5c59f8720589d0de14b (diff) | |
| download | linux-34be98f4944f99076f049a6806fc5f5207a755d3.tar.bz2 | |
arm64: kernel: remove {THREAD,IRQ_STACK}_START_SP
For historical reasons, we leave the top 16 bytes of our task and IRQ
stacks unused, a practice used to ensure that the SP can always be
masked to find the base of the current stack (historically, where
thread_info could be found).
However, this is not necessary, as:
* When an exception is taken from a task stack, we decrement the SP by
S_FRAME_SIZE and stash the exception registers before we compare the
SP against the task stack. In such cases, the SP must be at least
S_FRAME_SIZE below the limit, and can be safely masked to determine
whether the task stack is in use.
* When transitioning to an IRQ stack, we'll place a dummy frame onto the
IRQ stack before enabling asynchronous exceptions, or executing code
we expect to trigger faults. Thus, if an exception is taken from the
IRQ stack, the SP must be at least 16 bytes below the limit.
* We no longer mask the SP to find the thread_info, which is now found
via sp_el0. Note that historically, the offset was critical to ensure
that cpu_switch_to() found the correct stack for new threads that
hadn't yet executed ret_from_fork().
Given that, this initial offset serves no purpose, and can be removed.
This brings us in-line with other architectures (e.g. x86) which do not
rely on this masking.
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
[Mark: rebase, kill THREAD_START_SP, commit msg additions]
Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Reviewed-by: Will Deacon <will.deacon@arm.com>
Tested-by: Laura Abbott <labbott@redhat.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: James Morse <james.morse@arm.com>
Diffstat (limited to 'arch/arm64/kernel')
| -rw-r--r-- | arch/arm64/kernel/entry.S | 2 | ||||
| -rw-r--r-- | arch/arm64/kernel/smp.c | 2 |
2 files changed, 2 insertions, 2 deletions
diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S index 612a077ba109..f31c7b26a686 100644 --- a/arch/arm64/kernel/entry.S +++ b/arch/arm64/kernel/entry.S @@ -272,7 +272,7 @@ alternative_else_nop_endif cbnz x25, 9998f adr_this_cpu x25, irq_stack, x26 - mov x26, #IRQ_STACK_START_SP + mov x26, #IRQ_STACK_SIZE add x26, x25, x26 /* switch to the irq stack */ diff --git a/arch/arm64/kernel/smp.c b/arch/arm64/kernel/smp.c index dc66e6ec3a99..f13ddb2404f9 100644 --- a/arch/arm64/kernel/smp.c +++ b/arch/arm64/kernel/smp.c @@ -154,7 +154,7 @@ int __cpu_up(unsigned int cpu, struct task_struct *idle) * page tables. */ secondary_data.task = idle; - secondary_data.stack = task_stack_page(idle) + THREAD_START_SP; + secondary_data.stack = task_stack_page(idle) + THREAD_SIZE; update_cpu_boot_status(CPU_MMU_OFF); __flush_dcache_area(&secondary_data, sizeof(secondary_data)); |