powerpc/64: remove support for kernel-mode syscalls

There is support for the kernel to execute the 'sc 0' instruction and
make a system call to itself. This is a relic that is unused in the
tree, therefore untested. It's also highly questionable for modules to
be doing this.

Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20190827033010.28090-3-npiggin@gmail.com

diff --git a/arch/powerpc/kernel/entry_64.S b/arch/powerpc/kernel/entry_64.S
index 0a0b531..6467bda 100644 (file)
--- a/arch/powerpc/kernel/entry_64.S
+++ b/arch/powerpc/kernel/entry_64.S
@@ -69,24 +69,20 @@ BEGIN_FTR_SECTION
        bne     .Ltabort_syscall
 END_FTR_SECTION_IFSET(CPU_FTR_TM)
 #endif
-       andi.   r10,r12,MSR_PR
        mr      r10,r1
-       addi    r1,r1,-INT_FRAME_SIZE
-       beq-    1f
        ld      r1,PACAKSAVE(r13)
-1:     std     r10,0(r1)
+       std     r10,0(r1)
        std     r11,_NIP(r1)
        std     r12,_MSR(r1)
        std     r0,GPR0(r1)
        std     r10,GPR1(r1)
-       beq     2f                      /* if from kernel mode */
 #ifdef CONFIG_PPC_FSL_BOOK3E
 START_BTB_FLUSH_SECTION
        BTB_FLUSH(r10)
 END_BTB_FLUSH_SECTION
 #endif
        ACCOUNT_CPU_USER_ENTRY(r13, r10, r11)
-2:     std     r2,GPR2(r1)
+       std     r2,GPR2(r1)
        std     r3,GPR3(r1)
        mfcr    r2
        std     r4,GPR4(r1)
@@ -122,14 +118,13 @@ END_BTB_FLUSH_SECTION
 
 #if defined(CONFIG_VIRT_CPU_ACCOUNTING_NATIVE) && defined(CONFIG_PPC_SPLPAR)
 BEGIN_FW_FTR_SECTION
-       beq     33f
-       /* if from user, see if there are any DTL entries to process */
+       /* see if there are any DTL entries to process */
        ld      r10,PACALPPACAPTR(r13)  /* get ptr to VPA */
        ld      r11,PACA_DTL_RIDX(r13)  /* get log read index */
        addi    r10,r10,LPPACA_DTLIDX
        LDX_BE  r10,0,r10               /* get log write index */
-       cmpd    cr1,r11,r10
-       beq+    cr1,33f
+       cmpd    r11,r10
+       beq+    33f
        bl      accumulate_stolen_time
        REST_GPR(0,r1)
        REST_4GPRS(3,r1)
@@ -203,6 +198,7 @@ system_call:                        /* label this so stack traces look sane */
        mtctr   r12
        bctrl                   /* Call handler */
 
+       /* syscall_exit can exit to kernel mode, via ret_from_kernel_thread */
 .Lsyscall_exit:
        std     r3,RESULT(r1)
 
@@ -216,11 +212,6 @@ system_call:                       /* label this so stack traces look sane */
        ld      r12, PACA_THREAD_INFO(r13)
 
        ld      r8,_MSR(r1)
-#ifdef CONFIG_PPC_BOOK3S
-       /* No MSR:RI on BookE */
-       andi.   r10,r8,MSR_RI
-       beq-    .Lunrecov_restore
-#endif
 
 /*
  * This is a few instructions into the actual syscall exit path (which actually

diff --git a/arch/powerpc/kernel/exceptions-64s.S b/arch/powerpc/kernel/exceptions-64s.S
index dded467..5208043 100644 (file)
--- a/arch/powerpc/kernel/exceptions-64s.S
+++ b/arch/powerpc/kernel/exceptions-64s.S
@@ -1522,8 +1522,6 @@ EXC_COMMON(trap_0b_common, 0xb00, unknown_exception)
  * system call / hypercall (0xc00, 0x4c00)
  *
  * The system call exception is invoked with "sc 0" and does not alter HV bit.
- * There is support for kernel code to invoke system calls but there are no
- * in-tree users.
  *
  * The hypercall is invoked with "sc 1" and sets HV=1.
  *