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

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

[Daniel Henrique Barboza]

Hi,

Starting on Linux 6.6 the QEMU RISC-V KVM driver now supports
KMV_GET_REG_LIST. This API will make it simpler for the QEMU KVM driver
to determine whether a KVM reg is present or not.

We'll use this API to fetch ISA_EXT regs during init(). The current
logic will be put in a legacy() helper and will still be used in case
the host KVM module does not support get-reg-list.

Patch 1 contains error handling changes in kvm_riscv_init_multiext_cfg()
where we're using &error_fatal and errno. 


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, 95 insertions(+), 5 deletions(-)

-- 
2.41.0

[PATCH 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

Use "error_setg(&error_fatal, ..." since it'll both print the error and
do an exit(EXIT_FAILURE) in one single call, allowing us to remove
error_report() and exit().

Finally, 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 | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/target/riscv/kvm/kvm-cpu.c b/target/riscv/kvm/kvm-cpu.c
index c6615cb807..847cb2876a 100644
--- a/target/riscv/kvm/kvm-cpu.c
+++ b/target/riscv/kvm/kvm-cpu.c
@@ -791,10 +791,9 @@ static void kvm_riscv_init_multiext_cfg(RISCVCPU *cpu, KVMScratchCPU *kvmcpu)
                 multi_ext_cfg->supported = false;
                 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);
-                exit(EXIT_FAILURE);
+                error_setg(&error_fatal, "Unable to read ISA_EXT "
+                           "KVM register %s, error code: %s",
+                           multi_ext_cfg->name, strerrorname_np(errno));
             }
         } else {
             multi_ext_cfg->supported = true;
-- 
2.41.0

[PATCH 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 | 93 +++++++++++++++++++++++++++++++++++++-
 1 file changed, 92 insertions(+), 1 deletion(-)

diff --git a/target/riscv/kvm/kvm-cpu.c b/target/riscv/kvm/kvm-cpu.c
index 847cb2876a..bef6610e1a 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;
@@ -811,6 +812,96 @@ 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_setg(&error_fatal, "Error when accessing get-reg-list, "
+                   "code: %s", strerrorname_np(errno));
+    }
+
+    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_setg(&error_fatal, "Error when reading KVM_GET_REG_LIST, "
+                   "code %s ", strerrorname_np(errno));
+    }
+
+    /* 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_setg(&error_fatal, "Unable to read ISA_EXT "
+                       "KVM register %s, error code: %s",
+                       multi_ext_cfg->name, strerrorname_np(errno));
+        }
+
+        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 1/2] target/riscv/kvm: improve 'init_multiext_cfg' error msg

[Philippe Mathieu-Daudé]

Hi Daniel,

On 3/10/23 13:32, 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
> 
> Use "error_setg(&error_fatal, ..." since it'll both print the error and
> do an exit(EXIT_FAILURE) in one single call, allowing us to remove
> error_report() and exit().
> 
> Finally, 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 | 7 +++----
>   1 file changed, 3 insertions(+), 4 deletions(-)
> 
> diff --git a/target/riscv/kvm/kvm-cpu.c b/target/riscv/kvm/kvm-cpu.c
> index c6615cb807..847cb2876a 100644
> --- a/target/riscv/kvm/kvm-cpu.c
> +++ b/target/riscv/kvm/kvm-cpu.c
> @@ -791,10 +791,9 @@ static void kvm_riscv_init_multiext_cfg(RISCVCPU *cpu, KVMScratchCPU *kvmcpu)
>                   multi_ext_cfg->supported = false;
>                   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);
> -                exit(EXIT_FAILURE);
> +                error_setg(&error_fatal, "Unable to read ISA_EXT "

See the documentation added in include/qapi/error.h by commit
10303f04b9 ("error: Improve documentation some more"):

   * Please don't error_setg(&error_fatal, ...), use error_report() and
   * exit(), because that's more obvious.

> +                           "KVM register %s, error code: %s",
> +                           multi_ext_cfg->name, strerrorname_np(errno));
>               }
>           } else {
>               multi_ext_cfg->supported = true;

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

[Alistair Francis]

On Tue, Oct 3, 2023 at 9:34 PM Daniel Henrique Barboza
<dbarboza@ventanamicro.com> wrote:
>
> Hi,
>
> Starting on Linux 6.6 the QEMU RISC-V KVM driver now supports
> KMV_GET_REG_LIST. This API will make it simpler for the QEMU KVM driver
> to determine whether a KVM reg is present or not.
>
> We'll use this API to fetch ISA_EXT regs during init(). The current
> logic will be put in a legacy() helper and will still be used in case
> the host KVM module does not support get-reg-list.
>
> Patch 1 contains error handling changes in kvm_riscv_init_multiext_cfg()
> where we're using &error_fatal and errno.
>
>
> Daniel Henrique Barboza (2):
>   target/riscv/kvm: improve 'init_multiext_cfg' error msg
>   target/riscv/kvm: support KVM_GET_REG_LIST

Thanks!

Applied to riscv-to-apply.next

Alistair

>
>  target/riscv/kvm/kvm-cpu.c | 100 +++++++++++++++++++++++++++++++++++--
>  1 file changed, 95 insertions(+), 5 deletions(-)
>
> --
> 2.41.0
>
>