[PATCH] target/loongarch/kvm: set pv features per vCPU in kvm_arch_init_vcpu

[PATCH] target/loongarch/kvm: set pv features per vCPU in kvm_arch_init_vcpu

[Tao Cui]

From: Tao Cui <cuitao@kylinos.cn>

kvm_set_pv_features() programs the KVM_FEATURE cpucfg attribute, which is a
per-vCPU setting. It was called from kvm_arch_put_registers() under a
function-local static guard, so it ran only once for the whole VM and only
the first vCPU actually got its pv features pushed to KVM.

Move the call to kvm_arch_init_vcpu(), which runs once per vCPU, right
after the pv features are computed, and drop the static guard.

Signed-off-by: Tao Cui <cuitao@kylinos.cn>
---
 target/loongarch/kvm/kvm.c | 15 ++++++---------
 1 file changed, 6 insertions(+), 9 deletions(-)

diff --git a/target/loongarch/kvm/kvm.c b/target/loongarch/kvm/kvm.c
index d6539c12ac..985812c828 100644
--- a/target/loongarch/kvm/kvm.c
+++ b/target/loongarch/kvm/kvm.c
@@ -816,7 +816,6 @@ int kvm_arch_get_registers(CPUState *cs, Error **errp)
 int kvm_arch_put_registers(CPUState *cs, KvmPutState level, Error **errp)
 {
     int ret;
-    static int once;
 
     ret = kvm_loongarch_put_regs_core(cs);
     if (ret) {
@@ -843,14 +842,6 @@ int kvm_arch_put_registers(CPUState *cs, KvmPutState level, Error **errp)
         return ret;
     }
 
-    if (!once) {
-        ret = kvm_set_pv_features(cs);
-        if (ret) {
-            return ret;
-        }
-        once = 1;
-    }
-
     if (level >= KVM_PUT_FULL_STATE) {
         /*
          * only KVM_PUT_FULL_STATE is required, kvm kernel will clear
@@ -1209,6 +1200,12 @@ int kvm_arch_init_vcpu(CPUState *cs)
         return ret;
     }
 
+    /* pv_features is a per-vCPU attribute; set it here, once per vCPU. */
+    ret = kvm_set_pv_features(cs);
+    if (ret < 0) {
+        return ret;
+    }
+
     ret = kvm_cpu_check_ptw(cs, &local_err);
     if (ret < 0) {
         error_report_err(local_err);
-- 
2.43.0

Re: [PATCH] target/loongarch/kvm: set pv features per vCPU in kvm_arch_init_vcpu

[Bibo Mao]

On 2026/6/25 上午9:53, Tao Cui wrote:
> From: Tao Cui <cuitao@kylinos.cn>
> 
> kvm_set_pv_features() programs the KVM_FEATURE cpucfg attribute, which is a
> per-vCPU setting. It was called from kvm_arch_put_registers() under a
> function-local static guard, so it ran only once for the whole VM and only
> the first vCPU actually got its pv features pushed to KVM.
> 
> Move the call to kvm_arch_init_vcpu(), which runs once per vCPU, right
> after the pv features are computed, and drop the static guard.
> 
> Signed-off-by: Tao Cui <cuitao@kylinos.cn>
> ---
>   target/loongarch/kvm/kvm.c | 15 ++++++---------
>   1 file changed, 6 insertions(+), 9 deletions(-)
> 
> diff --git a/target/loongarch/kvm/kvm.c b/target/loongarch/kvm/kvm.c
> index d6539c12ac..985812c828 100644
> --- a/target/loongarch/kvm/kvm.c
> +++ b/target/loongarch/kvm/kvm.c
> @@ -816,7 +816,6 @@ int kvm_arch_get_registers(CPUState *cs, Error **errp)
>   int kvm_arch_put_registers(CPUState *cs, KvmPutState level, Error **errp)
>   {
>       int ret;
> -    static int once;
>   
>       ret = kvm_loongarch_put_regs_core(cs);
>       if (ret) {
> @@ -843,14 +842,6 @@ int kvm_arch_put_registers(CPUState *cs, KvmPutState level, Error **errp)
>           return ret;
>       }
>   
> -    if (!once) {
> -        ret = kvm_set_pv_features(cs);
> -        if (ret) {
> -            return ret;
> -        }
> -        once = 1;
> -    }
> -
>       if (level >= KVM_PUT_FULL_STATE) {
>           /*
>            * only KVM_PUT_FULL_STATE is required, kvm kernel will clear
> @@ -1209,6 +1200,12 @@ int kvm_arch_init_vcpu(CPUState *cs)
>           return ret;
>       }
>   
> +    /* pv_features is a per-vCPU attribute; set it here, once per vCPU. */
> +    ret = kvm_set_pv_features(cs);
> +    if (ret < 0) {
> +        return ret;
> +    }
I prefer the old method. The pv_features is one vCPU state instead, and 
it will be added in vCPU VMState if migration is supported on different 
host kernel version.

Here is host feature detection, not vCPU state setting.

Regards
Bibo Mao
> +
>       ret = kvm_cpu_check_ptw(cs, &local_err);
>       if (ret < 0) {
>           error_report_err(local_err);
>