target-arm: Implement AArch64 OSLAR/OSLSR_EL1 sysregs

Added oslar_write function to OSLAR_EL1 sysreg, using a status variable
in ARMCPUState.cp15 struct (oslsr_el1). This variable is also linked
to the newly added read-only OSLSR_EL1 register.

Linux reads from this register during its suspend/resume procedure.
Signed-off-by: NDavorin Mista <davorin.mista@aggios.com>
[PMM: folded a long line and tweaked a comment]
Reviewed-by: NPeter Maydell <peter.maydell@linaro.org>
Signed-off-by: NPeter Maydell <peter.maydell@linaro.org>

target-arm/cpu.h

@@ -379,6 +379,7 @@ typedef struct CPUARMState {
         uint64_t dbgwvr[16]; /* watchpoint value registers */
         uint64_t dbgwcr[16]; /* watchpoint control registers */
         uint64_t mdscr_el1;
+        uint64_t oslsr_el1; /* OS Lock Status */
         /* If the counter is enabled, this stores the last time the counter
          * was reset. Otherwise it stores the counter value
          */

target-arm/helper.c

@@ -3568,6 +3568,23 @@ static CPAccessResult ctr_el0_access(CPUARMState *env, const ARMCPRegInfo *ri)
     return CP_ACCESS_OK;
 }
 
+static void oslar_write(CPUARMState *env, const ARMCPRegInfo *ri,
+                        uint64_t value)
+{
+    /* Writes to OSLAR_EL1 may update the OS lock status, which can be
+     * read via a bit in OSLSR_EL1.
+     */
+    int oslock;
+
+    if (ri->state == ARM_CP_STATE_AA32) {
+        oslock = (value == 0xC5ACCE55);
+    } else {
+        oslock = value & 1;
+    }
+
+    env->cp15.oslsr_el1 = deposit32(env->cp15.oslsr_el1, 1, 1, oslock);
+}
+
 static const ARMCPRegInfo debug_cp_reginfo[] = {
     /* DBGDRAR, DBGDSAR: always RAZ since we don't implement memory mapped
      * debug components. The AArch64 version of DBGDRAR is named MDRAR_EL1;
@@ -3596,10 +3613,14 @@ static const ARMCPRegInfo debug_cp_reginfo[] = {
       .type = ARM_CP_ALIAS,
       .access = PL1_R,
       .fieldoffset = offsetof(CPUARMState, cp15.mdscr_el1), },
-    /* We define a dummy WI OSLAR_EL1, because Linux writes to it. */
     { .name = "OSLAR_EL1", .state = ARM_CP_STATE_BOTH,
       .cp = 14, .opc0 = 2, .opc1 = 0, .crn = 1, .crm = 0, .opc2 = 4,
-      .access = PL1_W, .type = ARM_CP_NOP },
+      .access = PL1_W, .type = ARM_CP_NO_RAW,
+      .writefn = oslar_write },
+    { .name = "OSLSR_EL1", .state = ARM_CP_STATE_BOTH,
+      .cp = 14, .opc0 = 2, .opc1 = 0, .crn = 1, .crm = 1, .opc2 = 4,
+      .access = PL1_R, .resetvalue = 10,
+      .fieldoffset = offsetof(CPUARMState, cp15.oslsr_el1) },
     /* Dummy OSDLR_EL1: 32-bit Linux will read this */
     { .name = "OSDLR_EL1", .state = ARM_CP_STATE_BOTH,
       .cp = 14, .opc0 = 2, .opc1 = 0, .crn = 1, .crm = 3, .opc2 = 4,