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

Hi, Bibo,

On Thu, Jul 16, 2026 at 9:45 AM Bibo Mao <[email protected]> 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
> allow to set for many times, until vCPU starts to run.
>
> Signed-off-by: Bibo Mao <[email protected]>
> ---
>  arch/loongarch/include/asm/kvm_host.h |  4 +++-
>  arch/loongarch/kvm/vcpu.c             | 15 +++++++++++----
>  2 files changed, 14 insertions(+), 5 deletions(-)
>
> diff --git a/arch/loongarch/include/asm/kvm_host.h b/arch/loongarch/include/asm/kvm_host.h
> index 23cfbecebbd7..af376fc44c44 100644
> --- a/arch/loongarch/include/asm/kvm_host.h
> +++ b/arch/loongarch/include/asm/kvm_host.h
> @@ -163,7 +163,6 @@ 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 +249,9 @@ struct kvm_vcpu_arch {
>         /* cpucfg */
>         u32 cpucfg[KVM_MAX_CPUCFG_REGS];
>
> +       /* VCPU ran at least once */
> +       bool ran_atleast_once;
So long a name? Maybe has_run is enough?

Huacai
> +
>         /* paravirt steal time */
>         struct {
>                 u64 guest_addr;
> diff --git a/arch/loongarch/kvm/vcpu.c b/arch/loongarch/kvm/vcpu.c
> index 20c207d80e31..ce6a1b06d50d 100644
> --- a/arch/loongarch/kvm/vcpu.c
> +++ b/arch/loongarch/kvm/vcpu.c
> @@ -1164,11 +1164,14 @@ static int kvm_loongarch_cpucfg_set_attr(struct kvm_vcpu *vcpu,
>                 if (val & ~valid)
>                         return -EINVAL;
>
> -               /* All vCPUs need set the same PV features */
> -               if ((kvm->arch.pv_features & LOONGARCH_PV_FEAT_UPDATED)
> -                               && ((kvm->arch.pv_features & valid) != val))
> +               if ((kvm->arch.pv_features & valid) == val)
> +                       return 0;
> +
> +               if (vcpu->arch.ran_atleast_once)
>                         return -EINVAL;
> -               kvm->arch.pv_features = val | LOONGARCH_PV_FEAT_UPDATED;
> +
> +               /* All vCPUs need set the same PV features */
> +               kvm->arch.pv_features = val;
>                 return 0;
>         default:
>                 return -ENXIO;
> @@ -1851,6 +1854,10 @@ 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.ran_atleast_once)
> +               vcpu->arch.ran_atleast_once = true;
> +
>         if (vcpu->mmio_needed) {
>                 if (!vcpu->mmio_is_write)
>                         kvm_complete_mmio_read(vcpu, run);
>
> base-commit: a13c140cc289c0b7b3770bce5b3ad42ab35074aa
> --
> 2.39.3
>