arm64: Store struct thread_info in sp_el0

There is need for figuring out how to manage struct thread_info data when
IRQ stack is introduced. struct thread_info information should be copied
to IRQ stack under the current thread_info calculation logic whenever
context switching is invoked. This is too expensive to keep supporting
the approach.

Instead, this patch pays attention to sp_el0 which is an unused scratch
register in EL1 context. sp_el0 utilization not only simplifies the
management, but also prevents text section size from being increased
largely due to static allocated IRQ stack as removing masking operation
using THREAD_SIZE in many places.

Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Jungseok Lee <jungseoklee85@gmail.com>
Signed-off-by: James Morse <james.morse@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>

1 files changed, 12 insertions, 3 deletions

diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S
index e5b25389c48f..245fa6837880 100644
--- a/arch/arm64/kernel/entry.S
+++ b/arch/arm64/kernel/entry.S
@@ -88,7 +88,8 @@
 
         .if     \el == 0
         mrs     x21, sp_el0
-        get_thread_info tsk                     // Ensure MDSCR_EL1.SS is clear,
+        mov     tsk, sp
+        and     tsk, tsk, #~(THREAD_SIZE - 1)   // Ensure MDSCR_EL1.SS is clear,
         ldr     x19, [tsk, #TI_FLAGS]           // since we can unmask debug
         disable_step_tsk x19, x20               // exceptions when scheduling.
         .else
@@ -108,6 +109,13 @@
         .endif
 
         /*
+         * Set sp_el0 to current thread_info.
+         */
+        .if     \el == 0
+        msr     sp_el0, tsk
+        .endif
+
+        /*
          * Registers that may be useful after this macro is invoked:
          *
          * x21 - aborted SP
@@ -164,8 +172,7 @@ alternative_endif
         .endm
 
         .macro  get_thread_info, rd
-        mov     \rd, sp
-        and     \rd, \rd, #~(THREAD_SIZE - 1)   // top of stack
+        mrs     \rd, sp_el0
         .endm
 
 /*
@@ -599,6 +606,8 @@ ENTRY(cpu_switch_to)
         ldp     x29, x9, [x8], #16
         ldr     lr, [x8]
         mov     sp, x9
+        and     x9, x9, #~(THREAD_SIZE - 1)
+        msr     sp_el0, x9
         ret
 ENDPROC(cpu_switch_to)