[Qemu-devel] [PATCH v2 7/7] linux-user: Implement aarch64 PR_SVE_SET/GET_VL

[Richard Henderson <richard.henderson@linaro.org>]

As an implementation choice, widening VL has zeroed the
previously inaccessible portion of the sve registers.

Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
---
 target/arm/cpu.h     |  2 ++
 linux-user/syscall.c | 20 +++++++++++++++++
 target/arm/cpu64.c   | 61 ++++++++++++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 83 insertions(+)

diff --git a/target/arm/cpu.h b/target/arm/cpu.h
index 51a3e16275..8e1016cfd6 100644
--- a/target/arm/cpu.h
+++ b/target/arm/cpu.h
@@ -842,6 +842,8 @@ int arm_cpu_write_elf32_note(WriteCoreDumpFunction f, CPUState *cs,
 #ifdef TARGET_AARCH64
 int aarch64_cpu_gdb_read_register(CPUState *cpu, uint8_t *buf, int reg);
 int aarch64_cpu_gdb_write_register(CPUState *cpu, uint8_t *buf, int reg);
+unsigned aarch64_get_sve_vlen(CPUARMState *env);
+unsigned aarch64_set_sve_vlen(CPUARMState *env, unsigned vlen);
 #endif
 
 target_ulong do_arm_semihosting(CPUARMState *env);
diff --git a/linux-user/syscall.c b/linux-user/syscall.c
index 82b35a6bdf..4840bf502f 100644
--- a/linux-user/syscall.c
+++ b/linux-user/syscall.c
@@ -10659,6 +10659,26 @@ abi_long do_syscall(void *cpu_env, int num, abi_long arg1,
             break;
         }
 #endif
+#ifdef TARGET_AARCH64
+        case 50: /* PR_SVE_SET_VL */
+            /* We cannot support either PR_SVE_SET_VL_ONEXEC
+               or PR_SVE_VL_INHERIT.  Therefore, anything above
+               ARM_MAX_VQ results in EINVAL.  */
+            if (!arm_feature(cpu_env, ARM_FEATURE_SVE)
+                || arg2 > ARM_MAX_VQ * 16 || arg2 & 15) {
+                ret = -TARGET_EINVAL;
+            } else {
+                ret = aarch64_set_sve_vlen(cpu_env, arg2);
+            }
+            break;
+        case 51: /* PR_SVE_GET_VL */
+            if (arm_feature(cpu_env, ARM_FEATURE_SVE)) {
+                ret = aarch64_get_sve_vlen(cpu_env);
+            } else {
+                ret = -TARGET_EINVAL;
+            }
+            break;
+#endif /* AARCH64 */
         case PR_GET_SECCOMP:
         case PR_SET_SECCOMP:
             /* Disable seccomp to prevent the target disabling syscalls we
diff --git a/target/arm/cpu64.c b/target/arm/cpu64.c
index 1c330adc28..6dee78f006 100644
--- a/target/arm/cpu64.c
+++ b/target/arm/cpu64.c
@@ -363,3 +363,64 @@ static void aarch64_cpu_register_types(void)
 }
 
 type_init(aarch64_cpu_register_types)
+
+/* Return the current cumulative SVE VLEN.  */
+unsigned aarch64_get_sve_vlen(CPUARMState *env)
+{
+    return ((env->vfp.zcr_el[1] & 0xf) + 1) * 16;
+}
+
+/* Set the cumulative ZCR.EL to VLEN, or the nearest supported value.
+   Return the new value.  */
+unsigned aarch64_set_sve_vlen(CPUARMState *env, unsigned vl)
+{
+    unsigned vq = vl / 16;
+    unsigned old_vq = (env->vfp.zcr_el[1] & 0xf) + 1;
+
+    if (vq < 1) {
+        vq = 1;
+    } else if (vq > ARM_MAX_VQ) {
+        vq = ARM_MAX_VQ;
+    }
+    env->vfp.zcr_el[1] = vq - 1;
+
+    /* The manual sez that when SVE is enabled and VL is widened the
+     * implementation is allowed to zero the previously inaccessible
+     * portion of the registers.  The corollary to that is that when
+     * SVE is enabled and VL is narrowed we are also allowed to zero
+     * the now inaccessible portion of the registers.
+     *
+     * The intent of this is that no predicate bit beyond VL is ever set.
+     * Which means that some operations on predicate registers themselves
+     * may operate on full uint64_t or even unrolled across the maximum
+     * uint64_t[4].  Performing 4 bits of host arithmetic unconditionally
+     * may well be cheaper than conditionals to restrict to the operation
+     * to the relevant portion of a uint16_t[16].
+     *
+     * ??? Need to move this somewhere else, so that it applies to
+     * changes to the real system registers and EL state changes.
+     */
+    if (vq < old_vq) {
+        unsigned i, j;
+        uint64_t pmask;
+
+        /* Zap the high bits of the zregs.  */
+        for (i = 0; i < 32; i++) {
+            memset(&env->vfp.zregs[i].d[2 * vq], 0, 16 * (ARM_MAX_VQ - vq));
+        }
+
+        /* Zap the high bits of the pregs and ffr.  */
+        pmask = 0;
+        if (vq & 3) {
+            pmask = ~(-1ULL << (16 * (vq & 3)));
+        }
+        for (j = vq / 4; j < ARM_MAX_VQ / 4; j++) {
+            for (i = 0; i < 17; ++i) {
+                env->vfp.pregs[i].p[j] &= pmask;
+            }
+            pmask = 0;
+        }
+    }
+
+    return vq * 16;
+}
-- 
2.14.3