linux-kernel - Re: [PATCH v2] LoongArch: KVM: Add more CPUCFG mask bit

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Message-ID: <CAAhV-H66uH1TpaKTsqNtSqKYUDatJWj+zAuw-MYE88BqOF0XTA@mail.gmail.com>
Date: Thu, 29 Jan 2026 17:26:49 +0800
From: Huacai Chen <chenhuacai@...nel.org>
To: Bibo Mao <maobibo@...ngson.cn>
Cc: WANG Xuerui <kernel@...0n.name>, Tianrui Zhao <zhaotianrui@...ngson.cn>, 
	loongarch@...ts.linux.dev, linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Subject: Re: [PATCH v2] LoongArch: KVM: Add more CPUCFG mask bit

Hi, Bibo,

On Mon, Jan 26, 2026 at 10:48 AM Bibo Mao <maobibo@...ngson.cn> wrote:
>
> With LA664 CPU there are more features supported which are indicated
> in CPUCFG2 bit24:30 and CPUCFG3 bit17 and bit 23. KVM hypervisor can
> not enable or disable these features and there is no KVM exception
> when instructions of these features are used in guest mode.
>
> Here add more CPUCFG mask support with LA664 CPU type.
>
> Signed-off-by: Bibo Mao <maobibo@...ngson.cn>
> ---
>   1. Rebase on the latest version since some common CPUCFG bit macro
>      definitions are merged.
>   2. Modifiy the comments explaining why it comes from feature detect
>      of host CPU.
> ---
>  arch/loongarch/kvm/vcpu.c | 15 +++++++++++++++
>  1 file changed, 15 insertions(+)
>
> diff --git a/arch/loongarch/kvm/vcpu.c b/arch/loongarch/kvm/vcpu.c
> index 656b954c1134..a9608469fa7a 100644
> --- a/arch/loongarch/kvm/vcpu.c
> +++ b/arch/loongarch/kvm/vcpu.c
> @@ -652,6 +652,8 @@ static int _kvm_setcsr(struct kvm_vcpu *vcpu, unsigned int id, u64 val)
>
>  static int _kvm_get_cpucfg_mask(int id, u64 *v)
>  {
> +       unsigned int config;
> +
>         if (id < 0 || id >= KVM_MAX_CPUCFG_REGS)
>                 return -EINVAL;
>
> @@ -684,9 +686,22 @@ static int _kvm_get_cpucfg_mask(int id, u64 *v)
>                 if (cpu_has_ptw)
>                         *v |= CPUCFG2_PTW;
>
> +               /*
> +                * The capability indication of some features are the same
> +                * between host CPU and guest vCPU, and there is no special
> +                * feature detect method with vCPU. Also KVM hypervisor can
> +                * not enable or disable these features.
> +                *
> +                * Here use host CPU detected features for vCPU
> +                */
> +               config = read_cpucfg(LOONGARCH_CPUCFG2);
> +               *v |= config & (CPUCFG2_FRECIPE | CPUCFG2_DIV32 | CPUCFG2_LAM_BH);
> +               *v |= config & (CPUCFG2_LAMCAS | CPUCFG2_LLACQ_SCREL | CPUCFG2_SCQ);
>                 return 0;
>         case LOONGARCH_CPUCFG3:
>                 *v = GENMASK(16, 0);
> +               config = read_cpucfg(LOONGARCH_CPUCFG3);
> +               *v |= config & (CPUCFG3_DBAR_HINTS | CPUCFG3_SLDORDER_STA);
What about adding CPUCFG3_ALDORDER_STA and CPUCFG3_ASTORDER_STA here, too?

Huacai

>                 return 0;
>         case LOONGARCH_CPUCFG4:
>         case LOONGARCH_CPUCFG5:
>
> base-commit: 63804fed149a6750ffd28610c5c1c98cce6bd377
> --
> 2.39.3
>
>