Commit 63648dd2 authored by Will Deacon's avatar Will Deacon

arm64: entry: use ldp/stp instead of push/pop when saving/restoring regs

The push/pop instructions can be suboptimal when saving/restoring large
amounts of data to/from the stack, for example on entry/exit from the
kernel. This is because:

  (1) They act on descending addresses (i.e. the newly decremented sp),
      which may defeat some hardware prefetchers

  (2) They introduce an implicit dependency between each instruction, as
      the sp has to be updated in order to resolve the address of the
      next access.

This patch removes the push/pop instructions from our kernel entry/exit
macros in favour of ldp/stp plus offset.
Signed-off-by: default avatarWill Deacon <will.deacon@arm.com>
parent d54e81f9
......@@ -64,25 +64,26 @@
#define BAD_ERROR 3
.macro kernel_entry, el, regsize = 64
sub sp, sp, #S_FRAME_SIZE - S_LR // room for LR, SP, SPSR, ELR
sub sp, sp, #S_FRAME_SIZE
.if \regsize == 32
mov w0, w0 // zero upper 32 bits of x0
.endif
push x28, x29
push x26, x27
push x24, x25
push x22, x23
push x20, x21
push x18, x19
push x16, x17
push x14, x15
push x12, x13
push x10, x11
push x8, x9
push x6, x7
push x4, x5
push x2, x3
push x0, x1
stp x0, x1, [sp, #16 * 0]
stp x2, x3, [sp, #16 * 1]
stp x4, x5, [sp, #16 * 2]
stp x6, x7, [sp, #16 * 3]
stp x8, x9, [sp, #16 * 4]
stp x10, x11, [sp, #16 * 5]
stp x12, x13, [sp, #16 * 6]
stp x14, x15, [sp, #16 * 7]
stp x16, x17, [sp, #16 * 8]
stp x18, x19, [sp, #16 * 9]
stp x20, x21, [sp, #16 * 10]
stp x22, x23, [sp, #16 * 11]
stp x24, x25, [sp, #16 * 12]
stp x26, x27, [sp, #16 * 13]
stp x28, x29, [sp, #16 * 14]
.if \el == 0
mrs x21, sp_el0
get_thread_info tsk // Ensure MDSCR_EL1.SS is clear,
......@@ -118,33 +119,31 @@
.if \el == 0
ct_user_enter
ldr x23, [sp, #S_SP] // load return stack pointer
msr sp_el0, x23
.endif
msr elr_el1, x21 // set up the return data
msr spsr_el1, x22
.if \ret
ldr x1, [sp, #S_X1] // preserve x0 (syscall return)
add sp, sp, S_X2
.else
pop x0, x1
.endif
pop x2, x3 // load the rest of the registers
pop x4, x5
pop x6, x7
pop x8, x9
msr elr_el1, x21 // set up the return data
msr spsr_el1, x22
.if \el == 0
msr sp_el0, x23
ldp x0, x1, [sp, #16 * 0]
.endif
pop x10, x11
pop x12, x13
pop x14, x15
pop x16, x17
pop x18, x19
pop x20, x21
pop x22, x23
pop x24, x25
pop x26, x27
pop x28, x29
ldr lr, [sp], #S_FRAME_SIZE - S_LR // load LR and restore SP
ldp x2, x3, [sp, #16 * 1]
ldp x4, x5, [sp, #16 * 2]
ldp x6, x7, [sp, #16 * 3]
ldp x8, x9, [sp, #16 * 4]
ldp x10, x11, [sp, #16 * 5]
ldp x12, x13, [sp, #16 * 6]
ldp x14, x15, [sp, #16 * 7]
ldp x16, x17, [sp, #16 * 8]
ldp x18, x19, [sp, #16 * 9]
ldp x20, x21, [sp, #16 * 10]
ldp x22, x23, [sp, #16 * 11]
ldp x24, x25, [sp, #16 * 12]
ldp x26, x27, [sp, #16 * 13]
ldp x28, x29, [sp, #16 * 14]
ldr lr, [sp, #S_LR]
add sp, sp, #S_FRAME_SIZE // restore sp
eret // return to kernel
.endm
......
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