[RFC PATCH RESEND 1/4] target/arm/kvm: Introduce helper to check target impl CPU support

[Shameer Kolothum <shameerkolothum@gmail.com>]

From: Shameer Kolothum <shameerali.kolothum.thodi@huawei.com>

The helper function will try to set the SMCCC filters for KVM vendor
hypercalls related to target implementation CPU support. It also
checks the kernel support for writable implementation ID registers
(MIDR/REVIDR/AIDR) and enables it.

Subsequent patches for Target Impl CPU support will make use of this
helper.

Signed-off-by: Shameer Kolothum <shameerali.kolothum.thodi@huawei.com>
---
 target/arm/kvm.c     | 72 ++++++++++++++++++++++++++++++++++++++++++++
 target/arm/kvm_arm.h | 12 ++++++++
 2 files changed, 84 insertions(+)

diff --git a/target/arm/kvm.c b/target/arm/kvm.c
index 3f41f99e23..eb04640b50 100644
--- a/target/arm/kvm.c
+++ b/target/arm/kvm.c
@@ -2072,6 +2072,78 @@ bool kvm_arm_mte_supported(void)
     return kvm_check_extension(kvm_state, KVM_CAP_ARM_MTE);
 }
 
+static bool kvm_arm_set_vm_attr(struct kvm_device_attr *attr, const char *name)
+{
+    int err;
+
+    err = kvm_vm_ioctl(kvm_state, KVM_HAS_DEVICE_ATTR, attr);
+    if (err != 0) {
+        error_report("%s: KVM_HAS_DEVICE_ATTR: %s", name, strerror(-err));
+        return false;
+    }
+
+    err = kvm_vm_ioctl(kvm_state, KVM_SET_DEVICE_ATTR, attr);
+    if (err != 0) {
+        error_report("%s: KVM_SET_DEVICE_ATTR: %s", name, strerror(-err));
+        return false;
+    }
+
+    return true;
+}
+
+static bool kvm_arm_set_smccc_filter(uint64_t func, uint8_t faction)
+{
+    struct kvm_smccc_filter filter = {
+        .base = func,
+        .nr_functions = 1,
+        .action = faction,
+    };
+    struct kvm_device_attr attr = {
+        .group = KVM_ARM_VM_SMCCC_CTRL,
+        .attr = KVM_ARM_VM_SMCCC_FILTER,
+        .flags = 0,
+        .addr = (uintptr_t)&filter,
+    };
+
+    if (!kvm_arm_set_vm_attr(&attr, "SMCCC Filter")) {
+        error_report("failed to set SMCCC filter in KVM Host");
+        return false;
+    }
+
+    return true;
+}
+
+bool kvm_arm_target_impl_cpus_supported(void)
+{
+    if (!kvm_arm_set_smccc_filter(
+        ARM_SMCCC_VENDOR_HYP_KVM_DISCOVER_IMPL_VER_FUNC_ID,
+        KVM_SMCCC_FILTER_FWD_TO_USER)) {
+        error_report("ARM_SMCCC_KVM_FUNC_DISCOVER_IMPL_VER fwd filter "
+                     "install failed");
+        return false;
+    }
+
+    if (!kvm_arm_set_smccc_filter(
+        ARM_SMCCC_VENDOR_HYP_KVM_DISCOVER_IMPL_CPUS_FUNC_ID,
+        KVM_SMCCC_FILTER_FWD_TO_USER)) {
+        error_report("ARM_SMCCC_KVM_FUNC_DISCOVER_IMPL_CPUS fwd filter "
+                     "install failed");
+        return false;
+    }
+
+    if (!kvm_check_extension(kvm_state, KVM_CAP_ARM_WRITABLE_IMP_ID_REGS)) {
+        error_report("KVM_CAP_ARM_WRITABLE_IMP_ID_REGS not supported");
+        return false;
+    }
+
+    if (kvm_vm_enable_cap(kvm_state, KVM_CAP_ARM_WRITABLE_IMP_ID_REGS, 0)) {
+        error_report("Failed to enable KVM_CAP_ARM_WRITABLE_IMP_ID_REGS cap");
+        return false;
+    }
+
+    return true;
+}
+
 QEMU_BUILD_BUG_ON(KVM_ARM64_SVE_VQ_MIN != 1);
 
 uint32_t kvm_arm_sve_get_vls(ARMCPU *cpu)
diff --git a/target/arm/kvm_arm.h b/target/arm/kvm_arm.h
index ba5de45f86..3cd6447901 100644
--- a/target/arm/kvm_arm.h
+++ b/target/arm/kvm_arm.h
@@ -207,6 +207,13 @@ bool kvm_arm_sve_supported(void);
  */
 bool kvm_arm_mte_supported(void);
 
+/**
+ * kvm_arm_target_impl_cpus_supported:
+ *
+ * Returns: true if KVM can enable target impl CPUs, and false otherwise.
+ */
+bool kvm_arm_target_impl_cpus_supported(void);
+
 /**
  * kvm_arm_get_max_vm_ipa_size:
  * @ms: Machine state handle
@@ -263,6 +270,11 @@ static inline bool kvm_arm_mte_supported(void)
     return false;
 }
 
+static inline bool kvm_arm_target_impl_cpus_supported(void)
+{
+    return false;
+}
+
 static inline int kvm_arm_get_writable_id_regs(ARMCPU *cpu, IdRegMap *idregmap)
 {
     return -ENOSYS;
-- 
2.34.1