Re: [PATCH v2] LoongArch: KVM: Allow to set pv_feature until vCPU run

[Huacai Chen]

Applied, thanks.


Huacai

On Thu, Sep 10, 2026 at 10:28 AM Bibo Mao <maobibo@xxxxxxxxxxx> wrote:
>
> Now pv_feature can be set only once, there is problem with VM migration.
> Where it is set when vCPU is created and after migration, here it is
> allowed to set for many times, until vCPU starts to run.
>
> Signed-off-by: Bibo Mao <maobibo@xxxxxxxxxxx>
> ---
> v1 ... v2:
>   1. Rename ran_atleast_once with has_run for simplity.
>   2. Rebase on the latest version where there is pv_setting_lock
>      protection when modify pv_features of VM.
> ---
>  arch/loongarch/include/asm/kvm_host.h |  3 ++-
>  arch/loongarch/kvm/vcpu.c             | 15 ++++++++++++---
>  2 files changed, 14 insertions(+), 4 deletions(-)
>
> diff --git a/arch/loongarch/include/asm/kvm_host.h b/arch/loongarch/include/asm/kvm_host.h
> index 65d91c3ce313..4ee1a29a5ea0 100644
> --- a/arch/loongarch/include/asm/kvm_host.h
> +++ b/arch/loongarch/include/asm/kvm_host.h
> @@ -164,7 +164,6 @@ enum emulation_result {
>  #define KVM_LARCH_SWCSR_LATEST (0x1 << 3)
>  #define KVM_LARCH_HWCSR_USABLE (0x1 << 4)
>
> -#define LOONGARCH_PV_FEAT_UPDATED      BIT_ULL(63)
>  #define LOONGARCH_PV_FEAT_MASK         (BIT(KVM_FEATURE_IPI) |         \
>                                          BIT(KVM_FEATURE_PREEMPT) |     \
>                                          BIT(KVM_FEATURE_STEAL_TIME) |  \
> @@ -250,6 +249,8 @@ struct kvm_vcpu_arch {
>         struct dmsintc_state dmsintc_state;
>         /* cpucfg */
>         u32 cpucfg[KVM_MAX_CPUCFG_REGS];
> +       /* VCPU ran at least once */
> +       bool has_run;
>
>         /* paravirt steal time */
>         struct {
> diff --git a/arch/loongarch/kvm/vcpu.c b/arch/loongarch/kvm/vcpu.c
> index 8e028be3f0a9..dbf87ac5252b 100644
> --- a/arch/loongarch/kvm/vcpu.c
> +++ b/arch/loongarch/kvm/vcpu.c
> @@ -1166,12 +1166,17 @@ static int kvm_loongarch_cpucfg_set_attr(struct kvm_vcpu *vcpu,
>
>                 /* All vCPUs need set the same PV features */
>                 spin_lock(&kvm->arch.pv_setting_lock);
> -               if ((kvm->arch.pv_features & LOONGARCH_PV_FEAT_UPDATED)
> -                               && ((kvm->arch.pv_features & valid) != val)) {
> +               if ((kvm->arch.pv_features & valid) == val) {
> +                       spin_unlock(&kvm->arch.pv_setting_lock);
> +                       return 0;
> +               }
> +
> +               if (vcpu->arch.has_run) {
>                         spin_unlock(&kvm->arch.pv_setting_lock);
>                         return -EINVAL;
>                 }
> -               kvm->arch.pv_features = val | LOONGARCH_PV_FEAT_UPDATED;
> +
> +               kvm->arch.pv_features = val;
>                 spin_unlock(&kvm->arch.pv_setting_lock);
>                 return 0;
>         default:
> @@ -1858,6 +1863,10 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu)
>         int r = -EINTR;
>         struct kvm_run *run = vcpu->run;
>
> +       /* Mark this VCPU ran at least once */
> +       if (!vcpu->arch.has_run)
> +               vcpu->arch.has_run = true;
> +
>         if (vcpu->mmio_needed) {
>                 if (!vcpu->mmio_is_write)
>                         kvm_complete_mmio_read(vcpu, run);
>
> base-commit: df2908090cda368b01ff43709f51890076c56157
> --
> 2.39.3
>