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

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Message-ID: <60b5e543-226c-3c15-09ed-c3c5ccfeb699@loongson.cn>
Date: Thu, 29 Jan 2026 17:57:24 +0800
From: Bibo Mao <maobibo@...ngson.cn>
To: Huacai Chen <chenhuacai@...nel.org>
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



On 2026/1/29 下午5:26, Huacai Chen wrote:
> 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?
I am ok to add these bits.

It is strange that there is both capability bit and status bit. AFAIK 
cpucfg is read-only, status bit means that it will change at runtime. I 
will negotiate with HW guys about these bits.

Regards
Bibo Mao
> 
> Huacai
> 
>>                  return 0;
>>          case LOONGARCH_CPUCFG4:
>>          case LOONGARCH_CPUCFG5:
>>
>> base-commit: 63804fed149a6750ffd28610c5c1c98cce6bd377
>> --
>> 2.39.3
>>
>>