target/riscv/kvm: implement SBI debug console (DBCN) calls
SBI defines a Debug Console extension "DBCN" that will, in time, replace
the legacy console putchar and getchar SBI extensions.
The appeal of the DBCN extension is that it allows multiple bytes to be
read/written in the SBI console in a single SBI call.
As far as KVM goes, the DBCN calls are forwarded by an in-kernel KVM
module to userspace. But this will only happens if the KVM module
actually supports this SBI extension and we activate it.
We'll check for DBCN support during init time, checking if get-reg-list
is advertising KVM_RISCV_SBI_EXT_DBCN. In that case, we'll enable it via
kvm_set_one_reg() during kvm_arch_init_vcpu().
Finally, change kvm_riscv_handle_sbi() to handle the incoming calls for
SBI_EXT_DBCN, reading and writing as required.
A simple KVM guest with 'earlycon=sbi', running in an emulated RISC-V
host, takes around 20 seconds to boot without using DBCN. With this
patch we're taking around 14 seconds to boot due to the speed-up in the
terminal output. There's no change in boot time if the guest isn't
using earlycon.
Signed-off-by: Daniel Henrique Barboza <dbarboza@ventanamicro.com>
Reviewed-by: Andrew Jones <ajones@ventanamicro.com>
Message-ID: <20240425155012.581366-1-dbarboza@ventanamicro.com>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>
diff --git a/target/riscv/kvm/kvm-cpu.c b/target/riscv/kvm/kvm-cpu.c
index b8136c7..d2491d8 100644
--- a/target/riscv/kvm/kvm-cpu.c
+++ b/target/riscv/kvm/kvm-cpu.c
@@ -409,6 +409,12 @@
KVM_REG_RISCV_VECTOR_CSR_REG(vlenb)
};
+static KVMCPUConfig kvm_sbi_dbcn = {
+ .name = "sbi_dbcn",
+ .kvm_reg_id = KVM_REG_RISCV | KVM_REG_SIZE_U64 |
+ KVM_REG_RISCV_SBI_EXT | KVM_RISCV_SBI_EXT_DBCN
+};
+
static void kvm_riscv_update_cpu_cfg_isa_ext(RISCVCPU *cpu, CPUState *cs)
{
CPURISCVState *env = &cpu->env;
@@ -1037,6 +1043,20 @@
return 0;
}
+static void kvm_riscv_check_sbi_dbcn_support(RISCVCPU *cpu,
+ KVMScratchCPU *kvmcpu,
+ struct kvm_reg_list *reglist)
+{
+ struct kvm_reg_list *reg_search;
+
+ reg_search = bsearch(&kvm_sbi_dbcn.kvm_reg_id, reglist->reg, reglist->n,
+ sizeof(uint64_t), uint64_cmp);
+
+ if (reg_search) {
+ kvm_sbi_dbcn.supported = true;
+ }
+}
+
static void kvm_riscv_read_vlenb(RISCVCPU *cpu, KVMScratchCPU *kvmcpu,
struct kvm_reg_list *reglist)
{
@@ -1142,6 +1162,8 @@
if (riscv_has_ext(&cpu->env, RVV)) {
kvm_riscv_read_vlenb(cpu, kvmcpu, reglist);
}
+
+ kvm_riscv_check_sbi_dbcn_support(cpu, kvmcpu, reglist);
}
static void riscv_init_kvm_registers(Object *cpu_obj)
@@ -1316,6 +1338,17 @@
return ret;
}
+static int kvm_vcpu_enable_sbi_dbcn(RISCVCPU *cpu, CPUState *cs)
+{
+ target_ulong reg = 1;
+
+ if (!kvm_sbi_dbcn.supported) {
+ return 0;
+ }
+
+ return kvm_set_one_reg(cs, kvm_sbi_dbcn.kvm_reg_id, ®);
+}
+
int kvm_arch_init_vcpu(CPUState *cs)
{
int ret = 0;
@@ -1333,6 +1366,8 @@
kvm_riscv_update_cpu_misa_ext(cpu, cs);
kvm_riscv_update_cpu_cfg_isa_ext(cpu, cs);
+ ret = kvm_vcpu_enable_sbi_dbcn(cpu, cs);
+
return ret;
}
@@ -1390,6 +1425,79 @@
return true;
}
+static void kvm_riscv_handle_sbi_dbcn(CPUState *cs, struct kvm_run *run)
+{
+ g_autofree uint8_t *buf = NULL;
+ RISCVCPU *cpu = RISCV_CPU(cs);
+ target_ulong num_bytes;
+ uint64_t addr;
+ unsigned char ch;
+ int ret;
+
+ switch (run->riscv_sbi.function_id) {
+ case SBI_EXT_DBCN_CONSOLE_READ:
+ case SBI_EXT_DBCN_CONSOLE_WRITE:
+ num_bytes = run->riscv_sbi.args[0];
+
+ if (num_bytes == 0) {
+ run->riscv_sbi.ret[0] = SBI_SUCCESS;
+ run->riscv_sbi.ret[1] = 0;
+ break;
+ }
+
+ addr = run->riscv_sbi.args[1];
+
+ /*
+ * Handle the case where a 32 bit CPU is running in a
+ * 64 bit addressing env.
+ */
+ if (riscv_cpu_mxl(&cpu->env) == MXL_RV32) {
+ addr |= (uint64_t)run->riscv_sbi.args[2] << 32;
+ }
+
+ buf = g_malloc0(num_bytes);
+
+ if (run->riscv_sbi.function_id == SBI_EXT_DBCN_CONSOLE_READ) {
+ ret = qemu_chr_fe_read_all(serial_hd(0)->be, buf, num_bytes);
+ if (ret < 0) {
+ error_report("SBI_EXT_DBCN_CONSOLE_READ: error when "
+ "reading chardev");
+ exit(1);
+ }
+
+ cpu_physical_memory_write(addr, buf, ret);
+ } else {
+ cpu_physical_memory_read(addr, buf, num_bytes);
+
+ ret = qemu_chr_fe_write_all(serial_hd(0)->be, buf, num_bytes);
+ if (ret < 0) {
+ error_report("SBI_EXT_DBCN_CONSOLE_WRITE: error when "
+ "writing chardev");
+ exit(1);
+ }
+ }
+
+ run->riscv_sbi.ret[0] = SBI_SUCCESS;
+ run->riscv_sbi.ret[1] = ret;
+ break;
+ case SBI_EXT_DBCN_CONSOLE_WRITE_BYTE:
+ ch = run->riscv_sbi.args[0];
+ ret = qemu_chr_fe_write(serial_hd(0)->be, &ch, sizeof(ch));
+
+ if (ret < 0) {
+ error_report("SBI_EXT_DBCN_CONSOLE_WRITE_BYTE: error when "
+ "writing chardev");
+ exit(1);
+ }
+
+ run->riscv_sbi.ret[0] = SBI_SUCCESS;
+ run->riscv_sbi.ret[1] = 0;
+ break;
+ default:
+ run->riscv_sbi.ret[0] = SBI_ERR_NOT_SUPPORTED;
+ }
+}
+
static int kvm_riscv_handle_sbi(CPUState *cs, struct kvm_run *run)
{
int ret = 0;
@@ -1408,6 +1516,9 @@
}
ret = 0;
break;
+ case SBI_EXT_DBCN:
+ kvm_riscv_handle_sbi_dbcn(cs, run);
+ break;
default:
qemu_log_mask(LOG_UNIMP,
"%s: un-handled SBI EXIT, specific reasons is %lu\n",
diff --git a/target/riscv/sbi_ecall_interface.h b/target/riscv/sbi_ecall_interface.h
index 43899d0..7dfe5f7 100644
--- a/target/riscv/sbi_ecall_interface.h
+++ b/target/riscv/sbi_ecall_interface.h
@@ -12,6 +12,17 @@
/* clang-format off */
+#define SBI_SUCCESS 0
+#define SBI_ERR_FAILED -1
+#define SBI_ERR_NOT_SUPPORTED -2
+#define SBI_ERR_INVALID_PARAM -3
+#define SBI_ERR_DENIED -4
+#define SBI_ERR_INVALID_ADDRESS -5
+#define SBI_ERR_ALREADY_AVAILABLE -6
+#define SBI_ERR_ALREADY_STARTED -7
+#define SBI_ERR_ALREADY_STOPPED -8
+#define SBI_ERR_NO_SHMEM -9
+
/* SBI Extension IDs */
#define SBI_EXT_0_1_SET_TIMER 0x0
#define SBI_EXT_0_1_CONSOLE_PUTCHAR 0x1
@@ -27,6 +38,7 @@
#define SBI_EXT_IPI 0x735049
#define SBI_EXT_RFENCE 0x52464E43
#define SBI_EXT_HSM 0x48534D
+#define SBI_EXT_DBCN 0x4442434E
/* SBI function IDs for BASE extension */
#define SBI_EXT_BASE_GET_SPEC_VERSION 0x0
@@ -57,6 +69,11 @@
#define SBI_EXT_HSM_HART_STOP 0x1
#define SBI_EXT_HSM_HART_GET_STATUS 0x2
+/* SBI function IDs for DBCN extension */
+#define SBI_EXT_DBCN_CONSOLE_WRITE 0x0
+#define SBI_EXT_DBCN_CONSOLE_READ 0x1
+#define SBI_EXT_DBCN_CONSOLE_WRITE_BYTE 0x2
+
#define SBI_HSM_HART_STATUS_STARTED 0x0
#define SBI_HSM_HART_STATUS_STOPPED 0x1
#define SBI_HSM_HART_STATUS_START_PENDING 0x2
