[PATCH v2 0/2] riscv, kvm: support KVM_GET_REG_LIST

[PATCH v2 0/2] riscv, kvm: support KVM_GET_REG_LIST

[Daniel Henrique Barboza]

Hi,

In this new version all instances of "error_setg(&error_fatal, ..." were
replaced with error_report() and exit(1), as suggested by Phil in v1.

No other changes made.

Changes from v1:
- patches 1 and 2:
  - replace 'error_setg(&error_fatal" with error_report() and exit(1)
- v1 link: https://lore.kernel.org/qemu-riscv/20231003113259.771539-1-dbarboza@ventanamicro.com/

Daniel Henrique Barboza (2):
  target/riscv/kvm: improve 'init_multiext_cfg' error msg
  target/riscv/kvm: support KVM_GET_REG_LIST

 target/riscv/kvm/kvm-cpu.c | 100 +++++++++++++++++++++++++++++++++++--
 1 file changed, 97 insertions(+), 3 deletions(-)

-- 
2.41.0

[PATCH v2 1/2] target/riscv/kvm: improve 'init_multiext_cfg' error msg

[Daniel Henrique Barboza]

Our error message is returning the value of 'ret', which will be always
-1 in case of error, and will not be that useful:

qemu-system-riscv64: Unable to read ISA_EXT KVM register ssaia, error -1

Improve the error message by outputting 'errno' instead of 'ret'. Use
strerrorname_np() to output the error name instead of the error code.
This will give us what we need to know right away:

qemu-system-riscv64: Unable to read ISA_EXT KVM register ssaia, error code: ENOENT

Given that we're going to exit(1) in this condition instead of
attempting to recover, remove the 'kvm_riscv_destroy_scratch_vcpu()'
call.

Signed-off-by: Daniel Henrique Barboza <dbarboza@ventanamicro.com>
---
 target/riscv/kvm/kvm-cpu.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/target/riscv/kvm/kvm-cpu.c b/target/riscv/kvm/kvm-cpu.c
index c6615cb807..c3daf74fe9 100644
--- a/target/riscv/kvm/kvm-cpu.c
+++ b/target/riscv/kvm/kvm-cpu.c
@@ -792,8 +792,8 @@ static void kvm_riscv_init_multiext_cfg(RISCVCPU *cpu, KVMScratchCPU *kvmcpu)
                 val = false;
             } else {
                 error_report("Unable to read ISA_EXT KVM register %s, "
-                             "error %d", multi_ext_cfg->name, ret);
-                kvm_riscv_destroy_scratch_vcpu(kvmcpu);
+                             "error code: %s", multi_ext_cfg->name,
+                             strerrorname_np(errno));
                 exit(EXIT_FAILURE);
             }
         } else {
-- 
2.41.0

[PATCH v2 2/2] target/riscv/kvm: support KVM_GET_REG_LIST

[Daniel Henrique Barboza]

KVM for RISC-V started supporting KVM_GET_REG_LIST in Linux 6.6. It
consists of a KVM ioctl() that retrieves a list of all available regs
for get_one_reg/set_one_reg. Regs that aren't present in the list aren't
supported in the host.

This simplifies our lives when initing the KVM regs since we don't have
to always attempt a KVM_GET_ONE_REG for all regs QEMU knows. We'll only
attempt a get_one_reg() if we're sure the reg is supported, i.e. it was
retrieved by KVM_GET_REG_LIST. Any error in get_one_reg() will then
always considered fatal, instead of having to handle special error codes
that might indicate a non-fatal failure.

Start by moving the current kvm_riscv_init_multiext_cfg() logic into a
new kvm_riscv_read_multiext_legacy() helper. We'll prioritize using
KVM_GET_REG_LIST, so check if we have it available and, in case we
don't, use the legacy() logic.

Otherwise, retrieve the available reg list and use it to check if the
host supports our known KVM regs, doing the usual get_one_reg() for
the supported regs and setting cpu->cfg accordingly.

Signed-off-by: Daniel Henrique Barboza <dbarboza@ventanamicro.com>
---
 target/riscv/kvm/kvm-cpu.c | 96 +++++++++++++++++++++++++++++++++++++-
 1 file changed, 95 insertions(+), 1 deletion(-)

diff --git a/target/riscv/kvm/kvm-cpu.c b/target/riscv/kvm/kvm-cpu.c
index c3daf74fe9..090d617627 100644
--- a/target/riscv/kvm/kvm-cpu.c
+++ b/target/riscv/kvm/kvm-cpu.c
@@ -771,7 +771,8 @@ static void kvm_riscv_read_cbomz_blksize(RISCVCPU *cpu, KVMScratchCPU *kvmcpu,
     }
 }
 
-static void kvm_riscv_init_multiext_cfg(RISCVCPU *cpu, KVMScratchCPU *kvmcpu)
+static void kvm_riscv_read_multiext_legacy(RISCVCPU *cpu,
+                                           KVMScratchCPU *kvmcpu)
 {
     CPURISCVState *env = &cpu->env;
     uint64_t val;
@@ -812,6 +813,99 @@ static void kvm_riscv_init_multiext_cfg(RISCVCPU *cpu, KVMScratchCPU *kvmcpu)
     }
 }
 
+static int uint64_cmp(const void *a, const void *b)
+{
+    uint64_t val1 = *(const uint64_t *)a;
+    uint64_t val2 = *(const uint64_t *)b;
+
+    if (val1 < val2) {
+        return -1;
+    }
+
+    if (val1 > val2) {
+        return 1;
+    }
+
+    return 0;
+}
+
+static void kvm_riscv_init_multiext_cfg(RISCVCPU *cpu, KVMScratchCPU *kvmcpu)
+{
+    KVMCPUConfig *multi_ext_cfg;
+    struct kvm_one_reg reg;
+    struct kvm_reg_list rl_struct;
+    struct kvm_reg_list *reglist;
+    uint64_t val, reg_id, *reg_search;
+    int i, ret;
+
+    rl_struct.n = 0;
+    ret = ioctl(kvmcpu->cpufd, KVM_GET_REG_LIST, &rl_struct);
+
+    /*
+     * If KVM_GET_REG_LIST isn't supported we'll get errno 22
+     * (EINVAL). Use read_legacy() in this case.
+     */
+    if (errno == EINVAL) {
+        return kvm_riscv_read_multiext_legacy(cpu, kvmcpu);
+    } else if (errno != E2BIG) {
+        /*
+         * E2BIG is an expected error message for the API since we
+         * don't know the number of registers. The right amount will
+         * be written in rl_struct.n.
+         *
+         * Error out if we get any other errno.
+         */
+        error_report("Error when accessing get-reg-list, code: %s",
+                     strerrorname_np(errno));
+        exit(EXIT_FAILURE);
+    }
+
+    reglist = g_malloc(sizeof(struct kvm_reg_list) +
+                       rl_struct.n * sizeof(uint64_t));
+    reglist->n = rl_struct.n;
+    ret = ioctl(kvmcpu->cpufd, KVM_GET_REG_LIST, reglist);
+    if (ret) {
+        error_report("Error when reading KVM_GET_REG_LIST, code %s ",
+                     strerrorname_np(errno));
+        exit(EXIT_FAILURE);
+    }
+
+    /* sort reglist to use bsearch() */
+    qsort(&reglist->reg, reglist->n, sizeof(uint64_t), uint64_cmp);
+
+    for (i = 0; i < ARRAY_SIZE(kvm_multi_ext_cfgs); i++) {
+        multi_ext_cfg = &kvm_multi_ext_cfgs[i];
+        reg_id = kvm_riscv_reg_id(&cpu->env, KVM_REG_RISCV_ISA_EXT,
+                                  multi_ext_cfg->kvm_reg_id);
+        reg_search = bsearch(&reg_id, reglist->reg, reglist->n,
+                             sizeof(uint64_t), uint64_cmp);
+        if (!reg_search) {
+            continue;
+        }
+
+        reg.id = reg_id;
+        reg.addr = (uint64_t)&val;
+        ret = ioctl(kvmcpu->cpufd, KVM_GET_ONE_REG, &reg);
+        if (ret != 0) {
+            error_report("Unable to read ISA_EXT KVM register %s, "
+                         "error code: %s", multi_ext_cfg->name,
+                         strerrorname_np(errno));
+            exit(EXIT_FAILURE);
+        }
+
+        multi_ext_cfg->supported = true;
+        kvm_cpu_cfg_set(cpu, multi_ext_cfg, val);
+    }
+
+    if (cpu->cfg.ext_icbom) {
+        kvm_riscv_read_cbomz_blksize(cpu, kvmcpu, &kvm_cbom_blocksize);
+    }
+
+    if (cpu->cfg.ext_icboz) {
+        kvm_riscv_read_cbomz_blksize(cpu, kvmcpu, &kvm_cboz_blocksize);
+    }
+}
+
 static void riscv_init_kvm_registers(Object *cpu_obj)
 {
     RISCVCPU *cpu = RISCV_CPU(cpu_obj);
-- 
2.41.0

Re: [PATCH v2 1/2] target/riscv/kvm: improve 'init_multiext_cfg' error msg

[Philippe Mathieu-Daudé]

On 3/10/23 15:21, Daniel Henrique Barboza wrote:
> Our error message is returning the value of 'ret', which will be always
> -1 in case of error, and will not be that useful:
> 
> qemu-system-riscv64: Unable to read ISA_EXT KVM register ssaia, error -1
> 
> Improve the error message by outputting 'errno' instead of 'ret'. Use
> strerrorname_np() to output the error name instead of the error code.
> This will give us what we need to know right away:
> 
> qemu-system-riscv64: Unable to read ISA_EXT KVM register ssaia, error code: ENOENT
> 
> Given that we're going to exit(1) in this condition instead of
> attempting to recover, remove the 'kvm_riscv_destroy_scratch_vcpu()'
> call.
> 
> Signed-off-by: Daniel Henrique Barboza <dbarboza@ventanamicro.com>
> ---
>   target/riscv/kvm/kvm-cpu.c | 4 ++--
>   1 file changed, 2 insertions(+), 2 deletions(-)

Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>

Re: [PATCH v2 1/2] target/riscv/kvm: improve 'init_multiext_cfg' error msg

[Andrew Jones]

On Tue, Oct 03, 2023 at 10:21:47AM -0300, Daniel Henrique Barboza wrote:
> Our error message is returning the value of 'ret', which will be always
> -1 in case of error, and will not be that useful:
> 
> qemu-system-riscv64: Unable to read ISA_EXT KVM register ssaia, error -1
> 
> Improve the error message by outputting 'errno' instead of 'ret'. Use
> strerrorname_np() to output the error name instead of the error code.
> This will give us what we need to know right away:
> 
> qemu-system-riscv64: Unable to read ISA_EXT KVM register ssaia, error code: ENOENT
> 
> Given that we're going to exit(1) in this condition instead of
> attempting to recover, remove the 'kvm_riscv_destroy_scratch_vcpu()'
> call.
> 
> Signed-off-by: Daniel Henrique Barboza <dbarboza@ventanamicro.com>
> ---
>  target/riscv/kvm/kvm-cpu.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/target/riscv/kvm/kvm-cpu.c b/target/riscv/kvm/kvm-cpu.c
> index c6615cb807..c3daf74fe9 100644
> --- a/target/riscv/kvm/kvm-cpu.c
> +++ b/target/riscv/kvm/kvm-cpu.c
> @@ -792,8 +792,8 @@ static void kvm_riscv_init_multiext_cfg(RISCVCPU *cpu, KVMScratchCPU *kvmcpu)
>                  val = false;
>              } else {
>                  error_report("Unable to read ISA_EXT KVM register %s, "
> -                             "error %d", multi_ext_cfg->name, ret);
> -                kvm_riscv_destroy_scratch_vcpu(kvmcpu);
> +                             "error code: %s", multi_ext_cfg->name,
> +                             strerrorname_np(errno));
>                  exit(EXIT_FAILURE);
>              }
>          } else {
> -- 
> 2.41.0
>

Reviewed-by: Andrew Jones <ajones@ventanamicro.com>

Re: [PATCH v2 2/2] target/riscv/kvm: support KVM_GET_REG_LIST

[Andrew Jones]

On Tue, Oct 03, 2023 at 10:21:48AM -0300, Daniel Henrique Barboza wrote:
> KVM for RISC-V started supporting KVM_GET_REG_LIST in Linux 6.6. It
> consists of a KVM ioctl() that retrieves a list of all available regs
> for get_one_reg/set_one_reg. Regs that aren't present in the list aren't
> supported in the host.
> 
> This simplifies our lives when initing the KVM regs since we don't have
> to always attempt a KVM_GET_ONE_REG for all regs QEMU knows. We'll only
> attempt a get_one_reg() if we're sure the reg is supported, i.e. it was
> retrieved by KVM_GET_REG_LIST. Any error in get_one_reg() will then
> always considered fatal, instead of having to handle special error codes
> that might indicate a non-fatal failure.
> 
> Start by moving the current kvm_riscv_init_multiext_cfg() logic into a
> new kvm_riscv_read_multiext_legacy() helper. We'll prioritize using
> KVM_GET_REG_LIST, so check if we have it available and, in case we
> don't, use the legacy() logic.
> 
> Otherwise, retrieve the available reg list and use it to check if the
> host supports our known KVM regs, doing the usual get_one_reg() for
> the supported regs and setting cpu->cfg accordingly.
> 
> Signed-off-by: Daniel Henrique Barboza <dbarboza@ventanamicro.com>
> ---
>  target/riscv/kvm/kvm-cpu.c | 96 +++++++++++++++++++++++++++++++++++++-
>  1 file changed, 95 insertions(+), 1 deletion(-)
> 
> diff --git a/target/riscv/kvm/kvm-cpu.c b/target/riscv/kvm/kvm-cpu.c
> index c3daf74fe9..090d617627 100644
> --- a/target/riscv/kvm/kvm-cpu.c
> +++ b/target/riscv/kvm/kvm-cpu.c
> @@ -771,7 +771,8 @@ static void kvm_riscv_read_cbomz_blksize(RISCVCPU *cpu, KVMScratchCPU *kvmcpu,
>      }
>  }
>  
> -static void kvm_riscv_init_multiext_cfg(RISCVCPU *cpu, KVMScratchCPU *kvmcpu)
> +static void kvm_riscv_read_multiext_legacy(RISCVCPU *cpu,
> +                                           KVMScratchCPU *kvmcpu)
>  {
>      CPURISCVState *env = &cpu->env;
>      uint64_t val;
> @@ -812,6 +813,99 @@ static void kvm_riscv_init_multiext_cfg(RISCVCPU *cpu, KVMScratchCPU *kvmcpu)
>      }
>  }
>  
> +static int uint64_cmp(const void *a, const void *b)
> +{
> +    uint64_t val1 = *(const uint64_t *)a;
> +    uint64_t val2 = *(const uint64_t *)b;
> +
> +    if (val1 < val2) {
> +        return -1;
> +    }
> +
> +    if (val1 > val2) {
> +        return 1;
> +    }
> +
> +    return 0;
> +}
> +
> +static void kvm_riscv_init_multiext_cfg(RISCVCPU *cpu, KVMScratchCPU *kvmcpu)
> +{
> +    KVMCPUConfig *multi_ext_cfg;
> +    struct kvm_one_reg reg;
> +    struct kvm_reg_list rl_struct;
> +    struct kvm_reg_list *reglist;
> +    uint64_t val, reg_id, *reg_search;
> +    int i, ret;
> +
> +    rl_struct.n = 0;
> +    ret = ioctl(kvmcpu->cpufd, KVM_GET_REG_LIST, &rl_struct);
> +
> +    /*
> +     * If KVM_GET_REG_LIST isn't supported we'll get errno 22
> +     * (EINVAL). Use read_legacy() in this case.
> +     */
> +    if (errno == EINVAL) {
> +        return kvm_riscv_read_multiext_legacy(cpu, kvmcpu);
> +    } else if (errno != E2BIG) {
> +        /*
> +         * E2BIG is an expected error message for the API since we
> +         * don't know the number of registers. The right amount will
> +         * be written in rl_struct.n.
> +         *
> +         * Error out if we get any other errno.
> +         */
> +        error_report("Error when accessing get-reg-list, code: %s",
> +                     strerrorname_np(errno));
> +        exit(EXIT_FAILURE);
> +    }
> +
> +    reglist = g_malloc(sizeof(struct kvm_reg_list) +
> +                       rl_struct.n * sizeof(uint64_t));
> +    reglist->n = rl_struct.n;
> +    ret = ioctl(kvmcpu->cpufd, KVM_GET_REG_LIST, reglist);
> +    if (ret) {
> +        error_report("Error when reading KVM_GET_REG_LIST, code %s ",
> +                     strerrorname_np(errno));
> +        exit(EXIT_FAILURE);
> +    }
> +
> +    /* sort reglist to use bsearch() */
> +    qsort(&reglist->reg, reglist->n, sizeof(uint64_t), uint64_cmp);
> +
> +    for (i = 0; i < ARRAY_SIZE(kvm_multi_ext_cfgs); i++) {
> +        multi_ext_cfg = &kvm_multi_ext_cfgs[i];
> +        reg_id = kvm_riscv_reg_id(&cpu->env, KVM_REG_RISCV_ISA_EXT,
> +                                  multi_ext_cfg->kvm_reg_id);
> +        reg_search = bsearch(&reg_id, reglist->reg, reglist->n,
> +                             sizeof(uint64_t), uint64_cmp);
> +        if (!reg_search) {
> +            continue;
> +        }
> +
> +        reg.id = reg_id;
> +        reg.addr = (uint64_t)&val;
> +        ret = ioctl(kvmcpu->cpufd, KVM_GET_ONE_REG, &reg);
> +        if (ret != 0) {
> +            error_report("Unable to read ISA_EXT KVM register %s, "
> +                         "error code: %s", multi_ext_cfg->name,
> +                         strerrorname_np(errno));
> +            exit(EXIT_FAILURE);
> +        }
> +
> +        multi_ext_cfg->supported = true;
> +        kvm_cpu_cfg_set(cpu, multi_ext_cfg, val);
> +    }
> +
> +    if (cpu->cfg.ext_icbom) {
> +        kvm_riscv_read_cbomz_blksize(cpu, kvmcpu, &kvm_cbom_blocksize);
> +    }
> +
> +    if (cpu->cfg.ext_icboz) {
> +        kvm_riscv_read_cbomz_blksize(cpu, kvmcpu, &kvm_cboz_blocksize);
> +    }
> +}
> +
>  static void riscv_init_kvm_registers(Object *cpu_obj)
>  {
>      RISCVCPU *cpu = RISCV_CPU(cpu_obj);
> -- 
> 2.41.0
>

Reviewed-by: Andrew Jones <ajones@ventanamicro.com>

Re: [PATCH v2 1/2] target/riscv/kvm: improve 'init_multiext_cfg' error msg

[Alistair Francis]

On Wed, Oct 4, 2023 at 12:46 AM Daniel Henrique Barboza
<dbarboza@ventanamicro.com> wrote:
>
> Our error message is returning the value of 'ret', which will be always
> -1 in case of error, and will not be that useful:
>
> qemu-system-riscv64: Unable to read ISA_EXT KVM register ssaia, error -1
>
> Improve the error message by outputting 'errno' instead of 'ret'. Use
> strerrorname_np() to output the error name instead of the error code.
> This will give us what we need to know right away:
>
> qemu-system-riscv64: Unable to read ISA_EXT KVM register ssaia, error code: ENOENT
>
> Given that we're going to exit(1) in this condition instead of
> attempting to recover, remove the 'kvm_riscv_destroy_scratch_vcpu()'
> call.
>
> Signed-off-by: Daniel Henrique Barboza <dbarboza@ventanamicro.com>

Reviewed-by: Alistair Francis <alistair.francis@wdc.com>

Alistair

> ---
>  target/riscv/kvm/kvm-cpu.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/target/riscv/kvm/kvm-cpu.c b/target/riscv/kvm/kvm-cpu.c
> index c6615cb807..c3daf74fe9 100644
> --- a/target/riscv/kvm/kvm-cpu.c
> +++ b/target/riscv/kvm/kvm-cpu.c
> @@ -792,8 +792,8 @@ static void kvm_riscv_init_multiext_cfg(RISCVCPU *cpu, KVMScratchCPU *kvmcpu)
>                  val = false;
>              } else {
>                  error_report("Unable to read ISA_EXT KVM register %s, "
> -                             "error %d", multi_ext_cfg->name, ret);
> -                kvm_riscv_destroy_scratch_vcpu(kvmcpu);
> +                             "error code: %s", multi_ext_cfg->name,
> +                             strerrorname_np(errno));
>                  exit(EXIT_FAILURE);
>              }
>          } else {
> --
> 2.41.0
>
>

Re: [PATCH v2 2/2] target/riscv/kvm: support KVM_GET_REG_LIST

[Alistair Francis]

On Wed, Oct 4, 2023 at 12:48 AM Daniel Henrique Barboza
<dbarboza@ventanamicro.com> wrote:
>
> KVM for RISC-V started supporting KVM_GET_REG_LIST in Linux 6.6. It
> consists of a KVM ioctl() that retrieves a list of all available regs
> for get_one_reg/set_one_reg. Regs that aren't present in the list aren't
> supported in the host.
>
> This simplifies our lives when initing the KVM regs since we don't have
> to always attempt a KVM_GET_ONE_REG for all regs QEMU knows. We'll only
> attempt a get_one_reg() if we're sure the reg is supported, i.e. it was
> retrieved by KVM_GET_REG_LIST. Any error in get_one_reg() will then
> always considered fatal, instead of having to handle special error codes
> that might indicate a non-fatal failure.
>
> Start by moving the current kvm_riscv_init_multiext_cfg() logic into a
> new kvm_riscv_read_multiext_legacy() helper. We'll prioritize using
> KVM_GET_REG_LIST, so check if we have it available and, in case we
> don't, use the legacy() logic.
>
> Otherwise, retrieve the available reg list and use it to check if the
> host supports our known KVM regs, doing the usual get_one_reg() for
> the supported regs and setting cpu->cfg accordingly.
>
> Signed-off-by: Daniel Henrique Barboza <dbarboza@ventanamicro.com>

Acked-by: Alistair Francis <alistair.francis@wdc.com>

Alistair

> ---
>  target/riscv/kvm/kvm-cpu.c | 96 +++++++++++++++++++++++++++++++++++++-
>  1 file changed, 95 insertions(+), 1 deletion(-)
>
> diff --git a/target/riscv/kvm/kvm-cpu.c b/target/riscv/kvm/kvm-cpu.c
> index c3daf74fe9..090d617627 100644
> --- a/target/riscv/kvm/kvm-cpu.c
> +++ b/target/riscv/kvm/kvm-cpu.c
> @@ -771,7 +771,8 @@ static void kvm_riscv_read_cbomz_blksize(RISCVCPU *cpu, KVMScratchCPU *kvmcpu,
>      }
>  }
>
> -static void kvm_riscv_init_multiext_cfg(RISCVCPU *cpu, KVMScratchCPU *kvmcpu)
> +static void kvm_riscv_read_multiext_legacy(RISCVCPU *cpu,
> +                                           KVMScratchCPU *kvmcpu)
>  {
>      CPURISCVState *env = &cpu->env;
>      uint64_t val;
> @@ -812,6 +813,99 @@ static void kvm_riscv_init_multiext_cfg(RISCVCPU *cpu, KVMScratchCPU *kvmcpu)
>      }
>  }
>
> +static int uint64_cmp(const void *a, const void *b)
> +{
> +    uint64_t val1 = *(const uint64_t *)a;
> +    uint64_t val2 = *(const uint64_t *)b;
> +
> +    if (val1 < val2) {
> +        return -1;
> +    }
> +
> +    if (val1 > val2) {
> +        return 1;
> +    }
> +
> +    return 0;
> +}
> +
> +static void kvm_riscv_init_multiext_cfg(RISCVCPU *cpu, KVMScratchCPU *kvmcpu)
> +{
> +    KVMCPUConfig *multi_ext_cfg;
> +    struct kvm_one_reg reg;
> +    struct kvm_reg_list rl_struct;
> +    struct kvm_reg_list *reglist;
> +    uint64_t val, reg_id, *reg_search;
> +    int i, ret;
> +
> +    rl_struct.n = 0;
> +    ret = ioctl(kvmcpu->cpufd, KVM_GET_REG_LIST, &rl_struct);
> +
> +    /*
> +     * If KVM_GET_REG_LIST isn't supported we'll get errno 22
> +     * (EINVAL). Use read_legacy() in this case.
> +     */
> +    if (errno == EINVAL) {
> +        return kvm_riscv_read_multiext_legacy(cpu, kvmcpu);
> +    } else if (errno != E2BIG) {
> +        /*
> +         * E2BIG is an expected error message for the API since we
> +         * don't know the number of registers. The right amount will
> +         * be written in rl_struct.n.
> +         *
> +         * Error out if we get any other errno.
> +         */
> +        error_report("Error when accessing get-reg-list, code: %s",
> +                     strerrorname_np(errno));
> +        exit(EXIT_FAILURE);
> +    }
> +
> +    reglist = g_malloc(sizeof(struct kvm_reg_list) +
> +                       rl_struct.n * sizeof(uint64_t));
> +    reglist->n = rl_struct.n;
> +    ret = ioctl(kvmcpu->cpufd, KVM_GET_REG_LIST, reglist);
> +    if (ret) {
> +        error_report("Error when reading KVM_GET_REG_LIST, code %s ",
> +                     strerrorname_np(errno));
> +        exit(EXIT_FAILURE);
> +    }
> +
> +    /* sort reglist to use bsearch() */
> +    qsort(&reglist->reg, reglist->n, sizeof(uint64_t), uint64_cmp);
> +
> +    for (i = 0; i < ARRAY_SIZE(kvm_multi_ext_cfgs); i++) {
> +        multi_ext_cfg = &kvm_multi_ext_cfgs[i];
> +        reg_id = kvm_riscv_reg_id(&cpu->env, KVM_REG_RISCV_ISA_EXT,
> +                                  multi_ext_cfg->kvm_reg_id);
> +        reg_search = bsearch(&reg_id, reglist->reg, reglist->n,
> +                             sizeof(uint64_t), uint64_cmp);
> +        if (!reg_search) {
> +            continue;
> +        }
> +
> +        reg.id = reg_id;
> +        reg.addr = (uint64_t)&val;
> +        ret = ioctl(kvmcpu->cpufd, KVM_GET_ONE_REG, &reg);
> +        if (ret != 0) {
> +            error_report("Unable to read ISA_EXT KVM register %s, "
> +                         "error code: %s", multi_ext_cfg->name,
> +                         strerrorname_np(errno));
> +            exit(EXIT_FAILURE);
> +        }
> +
> +        multi_ext_cfg->supported = true;
> +        kvm_cpu_cfg_set(cpu, multi_ext_cfg, val);
> +    }
> +
> +    if (cpu->cfg.ext_icbom) {
> +        kvm_riscv_read_cbomz_blksize(cpu, kvmcpu, &kvm_cbom_blocksize);
> +    }
> +
> +    if (cpu->cfg.ext_icboz) {
> +        kvm_riscv_read_cbomz_blksize(cpu, kvmcpu, &kvm_cboz_blocksize);
> +    }
> +}
> +
>  static void riscv_init_kvm_registers(Object *cpu_obj)
>  {
>      RISCVCPU *cpu = RISCV_CPU(cpu_obj);
> --
> 2.41.0
>
>