xtensa: introduce spill_registers_kernel macro

Most in-kernel users want registers spilled on the kernel stack and
don't require PS.EXCM to be set. That means that they don't need fixup
routine and could reuse regular window overflow mechanism for that,
which makes spill routine very simple.

Cc: stable@vger.kernel.org
Suggested-by: Chris Zankel <chris@zankel.net>
Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>

2 files changed, 76 insertions, 28 deletions

diff --git a/arch/xtensa/include/asm/traps.h b/arch/xtensa/include/asm/traps.h
index 8c194f6af45e..677bfcf4ee5d 100644
--- a/arch/xtensa/include/asm/traps.h
+++ b/arch/xtensa/include/asm/traps.h
@@ -23,25 +23,37 @@ void secondary_trap_init(void);
 
 static inline void spill_registers(void)
 {
-
+#if XCHAL_NUM_AREGS > 16
         __asm__ __volatile__ (
-                "movi   a14, "__stringify((1 << PS_EXCM_BIT) | LOCKLEVEL)"\n\t"
-                "mov    a12, a0\n\t"
-                "rsr    a13, sar\n\t"
-                "xsr    a14, ps\n\t"
-                "movi   a0, _spill_registers\n\t"
-                "rsync\n\t"
-                "callx0 a0\n\t"
-                "mov    a0, a12\n\t"
-                "wsr    a13, sar\n\t"
-                "wsr    a14, ps\n\t"
-                : :
-#if defined(CONFIG_FRAME_POINTER)
-                : "a2", "a3", "a4",       "a11", "a12", "a13", "a14", "a15",
+                "       call12  1f\n"
+                "       _j      2f\n"
+                "       retw\n"
+                "       .align  4\n"
+                "1:\n"
+                "       _entry  a1, 48\n"
+                "       addi    a12, a0, 3\n"
+#if XCHAL_NUM_AREGS > 32
+                "       .rept   (" __stringify(XCHAL_NUM_AREGS) " - 32) / 12\n"
+                "       _entry  a1, 48\n"
+                "       mov     a12, a0\n"
+                "       .endr\n"
+#endif
+                "       _entry  a1, 48\n"
+#if XCHAL_NUM_AREGS % 12 == 0
+                "       mov     a8, a8\n"
+#elif XCHAL_NUM_AREGS % 12 == 4
+                "       mov     a12, a12\n"
+#elif XCHAL_NUM_AREGS % 12 == 8
+                "       mov     a4, a4\n"
+#endif
+                "       retw\n"
+                "2:\n"
+                : : : "a12", "a13", "memory");
 #else
-                : "a2", "a3", "a4", "a7", "a11", "a12", "a13", "a14", "a15",
+        __asm__ __volatile__ (
+                "       mov     a12, a12\n"
+                : : : "memory");
 #endif
-                  "memory");
 }
 
 #endif /* _XTENSA_TRAPS_H */
diff --git a/arch/xtensa/kernel/entry.S b/arch/xtensa/kernel/entry.S
index 21dbe6bdb8ed..0489918e40d2 100644
--- a/arch/xtensa/kernel/entry.S
+++ b/arch/xtensa/kernel/entry.S
@@ -1794,6 +1794,43 @@ ENTRY(system_call)
 
 ENDPROC(system_call)
 
+/*
+ * Spill live registers on the kernel stack macro.
+ *
+ * Entry condition: ps.woe is set, ps.excm is cleared
+ * Exit condition: windowstart has single bit set
+ * May clobber: a12, a13
+ */
+        .macro  spill_registers_kernel
+
+#if XCHAL_NUM_AREGS > 16
+        call12  1f
+        _j      2f
+        retw
+        .align  4
+1:
+        _entry  a1, 48
+        addi    a12, a0, 3
+#if XCHAL_NUM_AREGS > 32
+        .rept   (XCHAL_NUM_AREGS - 32) / 12
+        _entry  a1, 48
+        mov     a12, a0
+        .endr
+#endif
+        _entry  a1, 48
+#if XCHAL_NUM_AREGS % 12 == 0
+        mov     a8, a8
+#elif XCHAL_NUM_AREGS % 12 == 4
+        mov     a12, a12
+#elif XCHAL_NUM_AREGS % 12 == 8
+        mov     a4, a4
+#endif
+        retw
+2:
+#else
+        mov     a12, a12
+#endif
+        .endm
 
 /*
  * Task switch.
@@ -1806,21 +1843,20 @@ ENTRY(_switch_to)
 
         entry   a1, 16
 
-        mov     a12, a2                 # preserve 'prev' (a2)
-        mov     a13, a3                 # and 'next' (a3)
+        mov     a10, a2                 # preserve 'prev' (a2)
+        mov     a11, a3                 # and 'next' (a3)
 
         l32i    a4, a2, TASK_THREAD_INFO
         l32i    a5, a3, TASK_THREAD_INFO
 
-        save_xtregs_user a4 a6 a8 a9 a10 a11 THREAD_XTREGS_USER
+        save_xtregs_user a4 a6 a8 a9 a12 a13 THREAD_XTREGS_USER
 
-        s32i    a0, a12, THREAD_RA      # save return address
-        s32i    a1, a12, THREAD_SP      # save stack pointer
+        s32i    a0, a10, THREAD_RA      # save return address
+        s32i    a1, a10, THREAD_SP      # save stack pointer
 
         /* Disable ints while we manipulate the stack pointer. */
 
-        movi    a14, (1 << PS_EXCM_BIT) | LOCKLEVEL
-        xsr     a14, ps
+        rsil    a14, LOCKLEVEL
         rsr     a3, excsave1
         rsync
         s32i    a3, a3, EXC_TABLE_FIXUP /* enter critical section */
@@ -1835,7 +1871,7 @@ ENTRY(_switch_to)
 
         /* Flush register file. */
 
-        call0   _spill_registers        # destroys a3, a4, and SAR
+        spill_registers_kernel
 
         /* Set kernel stack (and leave critical section)
          * Note: It's save to set it here. The stack will not be overwritten
@@ -1851,13 +1887,13 @@ ENTRY(_switch_to)
 
         /* restore context of the task 'next' */
 
-        l32i    a0, a13, THREAD_RA      # restore return address
-        l32i    a1, a13, THREAD_SP      # restore stack pointer
+        l32i    a0, a11, THREAD_RA      # restore return address
+        l32i    a1, a11, THREAD_SP      # restore stack pointer
 
-        load_xtregs_user a5 a6 a8 a9 a10 a11 THREAD_XTREGS_USER
+        load_xtregs_user a5 a6 a8 a9 a12 a13 THREAD_XTREGS_USER
 
         wsr     a14, ps
-        mov     a2, a12                 # return 'prev'
+        mov     a2, a10                 # return 'prev'
         rsync
 
         retw