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ARM: smp: Store current pointer in TPIDRURO register if available

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Now that the user space TLS register is assigned on every return to user
space, we can use it to keep the 'current' pointer while running in the
kernel. This removes the need to access it via thread_info, which is
located at the base of the stack, but will be moved out of there in a
subsequent patch.

Use the __builtin_thread_pointer() helper when available - this will
help GCC understand that reloading the value within the same function is
not necessary, even when using the per-task stack protector (which also
generates accesses via the TLS register). For example, the generated
code below loads TPIDRURO only once, and uses it to access both the
stack canary and the preempt_count fields.

<do_one_initcall>:
       e92d 41f0       stmdb   sp!, {r4, r5, r6, r7, r8, lr}
       ee1d 4f70       mrc     15, 0, r4, cr13, cr0, {3}
       4606            mov     r6, r0
       b094            sub     sp, #80 ; 0x50
       f8d4 34e8       ldr.w   r3, [r4, #1256] ; 0x4e8  <- stack canary
       9313            str     r3, [sp, #76]   ; 0x4c
       f8d4 8004       ldr.w   r8, [r4, #4]             <- preempt count

Co-developed-by: Keith Packard <keithpac@amazon.com>
Signed-off-by: Keith Packard <keithpac@amazon.com>
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Tested-by: Amit Daniel Kachhap <amit.kachhap@arm.com>
This commit is contained in:
Ard Biesheuvel
2021-09-18 10:44:37 +02:00
parent 3855ab614d
commit 50596b7559
12 changed files with 105 additions and 2 deletions
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24
arch/arm/include/asm/assembler.h
View File

@@ -199,6 +199,30 @@
.endm
.endr
.macro get_current, rd
#ifdef CONFIG_CURRENT_POINTER_IN_TPIDRURO
mrc p15, 0, \rd, c13, c0, 3 @ get TPIDRURO register
#else
get_thread_info \rd
ldr \rd, [\rd, #TI_TASK]
#endif
.endm
.macro set_current, rn
#ifdef CONFIG_CURRENT_POINTER_IN_TPIDRURO
mcr p15, 0, \rn, c13, c0, 3 @ set TPIDRURO register
#endif
.endm
.macro reload_current, t1:req, t2:req
#ifdef CONFIG_CURRENT_POINTER_IN_TPIDRURO
adr_l \t1, __entry_task @ get __entry_task base address
mrc p15, 0, \t2, c13, c0, 4 @ get per-CPU offset
ldr \t1, [\t1, \t2] @ load variable
mcr p15, 0, \t1, c13, c0, 3 @ store in TPIDRURO
#endif
.endm
/*
* Get current thread_info.
*/