[PATCH] target-arm: Add guest cpu endianness determination for virtio in KVM ARM64

[Pranavkumar Sawargaonkar <pranavkumar@xxxxxxxxxx>]

This patch implements a fucntion pointer virtio_is_big_endian()
from "CPUClass" structure for arm64.
Function aarch64_cpu_virtio_endianness() is added to determine and
returns the guest cpu endianness to virtio.
This is required for running cross endian guests with virtio on ARM64.

Signed-off-by: Pranavkumar Sawargaonkar <pranavkumar@xxxxxxxxxx>
---
 include/hw/virtio/virtio-access.h |  2 ++
 target-arm/cpu64.c                | 41 +++++++++++++++++++++++++++++++++++++++
 2 files changed, 43 insertions(+)

diff --git a/include/hw/virtio/virtio-access.h b/include/hw/virtio/virtio-access.h
index 46456fd..84fa701 100644
--- a/include/hw/virtio/virtio-access.h
+++ b/include/hw/virtio/virtio-access.h
@@ -23,6 +23,8 @@ static inline bool virtio_access_is_big_endian(VirtIODevice *vdev)
     return virtio_is_big_endian(vdev);
 #elif defined(TARGET_WORDS_BIGENDIAN)
     return true;
+#elif defined(TARGET_AARCH64)
+    return virtio_is_big_endian(vdev);
 #else
     return false;
 #endif
diff --git a/target-arm/cpu64.c b/target-arm/cpu64.c
index c30f47e..789f886 100644
--- a/target-arm/cpu64.c
+++ b/target-arm/cpu64.c
@@ -192,6 +192,43 @@ static void aarch64_cpu_set_pc(CPUState *cs, vaddr value)
     }
 }
 
+#ifndef CONFIG_USER_ONLY
+
+#define KVM_REG_ARM64_SCTLR_EL1 3, 0, 1, 0, 0
+
+static bool aarch64_cpu_virtio_endianness(CPUState *cs)
+{
+    ARMCPU *cpu = ARM_CPU(cs);
+    CPUARMState *env = &cpu->env;
+    struct kvm_one_reg reg;
+    uint64_t sctlr;
+
+    cpu_synchronize_state(cs);
+
+    /* Check if we are running 32bit guest or not */
+    if (!is_a64(env))
+        return (env->pstate & CPSR_E) ? 1 : 0;
+
+    /* Ideally we do not need to call IOCTL again to read SCTLR_EL1 value.
+     * cpu_synchronize_state() should fill the env->cp15.c1_sys
+     * to get this value but this path is currently not implemented for arm64.
+     * Hence this is a temporary fix.
+     */
+
+    reg.id = ARM64_SYS_REG(KVM_REG_ARM64_SCTLR_EL1);
+    reg.addr = (uint64_t) &sctlr;
+    kvm_vcpu_ioctl(cs, KVM_GET_ONE_REG, &reg);
+
+    if ((env->pstate & 0xf) == PSTATE_MODE_EL0t)
+        sctlr &= (1U <<24);
+    else
+        sctlr &= (1U <<25);
+
+    /* If BIG-ENDIAN return 1 */
+    return sctlr ? 1 : 0;
+}
+#endif
+
 static void aarch64_cpu_class_init(ObjectClass *oc, void *data)
 {
     CPUClass *cc = CPU_CLASS(oc);
@@ -203,6 +240,10 @@ static void aarch64_cpu_class_init(ObjectClass *oc, void *data)
     cc->gdb_write_register = aarch64_cpu_gdb_write_register;
     cc->gdb_num_core_regs = 34;
     cc->gdb_core_xml_file = "aarch64-core.xml";
+#ifndef CONFIG_USER_ONLY
+    cc->virtio_is_big_endian = aarch64_cpu_virtio_endianness;
+#endif
+
 }
 
 static void aarch64_cpu_register(const ARMCPUInfo *info)
-- 
1.9.1

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