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Subject: Re: [PATCH v5 3/6] LoongArch: KVM: Add cpucfg area for kvm hypervisor
To: Huacai Chen <chenhuacai@kernel.org>
Cc: Tianrui Zhao <zhaotianrui@loongson.cn>, Juergen Gross <jgross@suse.com>,
 Paolo Bonzini <pbonzini@redhat.com>, loongarch@lists.linux.dev,
 linux-kernel@vger.kernel.org, virtualization@lists.linux.dev,
 kvm@vger.kernel.org
References: <20240222032803.2177856-1-maobibo@loongson.cn>
 <20240222032803.2177856-4-maobibo@loongson.cn>
 <CAAhV-H5eqXMqTYVb6cAVqOsDNcEDeP9HzaMKw69KFQeVaAYEdA@mail.gmail.com>
From: maobibo <maobibo@loongson.cn>
Message-ID: <b6705098-1521-a892-9850-af84acd68674@loongson.cn>
Date: Mon, 26 Feb 2024 10:07:40 +0800
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On 2024/2/24 下午5:13, Huacai Chen wrote:
> Hi, Bibo,
> 
> On Thu, Feb 22, 2024 at 11:28 AM Bibo Mao <maobibo@loongson.cn> wrote:
>>
>> Instruction cpucfg can be used to get processor features. And there
>> is trap exception when it is executed in VM mode, and also it is
>> to provide cpu features to VM. On real hardware cpucfg area 0 - 20
>> is used.  Here one specified area 0x40000000 -- 0x400000ff is used
>> for KVM hypervisor to privide PV features, and the area can be extended
>> for other hypervisors in future. This area will never be used for
>> real HW, it is only used by software.
> After reading and thinking, I find that the hypercall method which is
> used in our productive kernel is better than this cpucfg method.
> Because hypercall is more simple and straightforward, plus we don't
> worry about conflicting with the real hardware.
About cpucfg area 0x40000000 -- 0x400000ff, I have negotiated with chip 
designer. This area will never be used with real hardware.

Regards
Bibo Mao
> 
> Huacai
> 
>>
>> Signed-off-by: Bibo Mao <maobibo@loongson.cn>
>> ---
>>   arch/loongarch/include/asm/inst.h      |  1 +
>>   arch/loongarch/include/asm/loongarch.h | 10 ++++++
>>   arch/loongarch/kvm/exit.c              | 46 +++++++++++++++++---------
>>   3 files changed, 41 insertions(+), 16 deletions(-)
>>
>> diff --git a/arch/loongarch/include/asm/inst.h b/arch/loongarch/include/asm/inst.h
>> index d8f637f9e400..ad120f924905 100644
>> --- a/arch/loongarch/include/asm/inst.h
>> +++ b/arch/loongarch/include/asm/inst.h
>> @@ -67,6 +67,7 @@ enum reg2_op {
>>          revhd_op        = 0x11,
>>          extwh_op        = 0x16,
>>          extwb_op        = 0x17,
>> +       cpucfg_op       = 0x1b,
>>          iocsrrdb_op     = 0x19200,
>>          iocsrrdh_op     = 0x19201,
>>          iocsrrdw_op     = 0x19202,
>> diff --git a/arch/loongarch/include/asm/loongarch.h b/arch/loongarch/include/asm/loongarch.h
>> index 46366e783c84..a1d22e8b6f94 100644
>> --- a/arch/loongarch/include/asm/loongarch.h
>> +++ b/arch/loongarch/include/asm/loongarch.h
>> @@ -158,6 +158,16 @@
>>   #define  CPUCFG48_VFPU_CG              BIT(2)
>>   #define  CPUCFG48_RAM_CG               BIT(3)
>>
>> +/*
>> + * cpucfg index area: 0x40000000 -- 0x400000ff
>> + * SW emulation for KVM hypervirsor
>> + */
>> +#define CPUCFG_KVM_BASE                        0x40000000UL
>> +#define CPUCFG_KVM_SIZE                        0x100
>> +#define CPUCFG_KVM_SIG                 CPUCFG_KVM_BASE
>> +#define  KVM_SIGNATURE                 "KVM\0"
>> +#define CPUCFG_KVM_FEATURE             (CPUCFG_KVM_BASE + 4)
>> +
>>   #ifndef __ASSEMBLY__
>>
>>   /* CSR */
>> diff --git a/arch/loongarch/kvm/exit.c b/arch/loongarch/kvm/exit.c
>> index 923bbca9bd22..6a38fd59d86d 100644
>> --- a/arch/loongarch/kvm/exit.c
>> +++ b/arch/loongarch/kvm/exit.c
>> @@ -206,10 +206,37 @@ int kvm_emu_idle(struct kvm_vcpu *vcpu)
>>          return EMULATE_DONE;
>>   }
>>
>> -static int kvm_trap_handle_gspr(struct kvm_vcpu *vcpu)
>> +static int kvm_emu_cpucfg(struct kvm_vcpu *vcpu, larch_inst inst)
>>   {
>>          int rd, rj;
>>          unsigned int index;
>> +
>> +       rd = inst.reg2_format.rd;
>> +       rj = inst.reg2_format.rj;
>> +       ++vcpu->stat.cpucfg_exits;
>> +       index = vcpu->arch.gprs[rj];
>> +
>> +       /*
>> +        * By LoongArch Reference Manual 2.2.10.5
>> +        * Return value is 0 for undefined cpucfg index
>> +        */
>> +       switch (index) {
>> +       case 0 ... (KVM_MAX_CPUCFG_REGS - 1):
>> +               vcpu->arch.gprs[rd] = vcpu->arch.cpucfg[index];
>> +               break;
>> +       case CPUCFG_KVM_SIG:
>> +               vcpu->arch.gprs[rd] = *(unsigned int *)KVM_SIGNATURE;
>> +               break;
>> +       default:
>> +               vcpu->arch.gprs[rd] = 0;
>> +               break;
>> +       }
>> +
>> +       return EMULATE_DONE;
>> +}
>> +
>> +static int kvm_trap_handle_gspr(struct kvm_vcpu *vcpu)
>> +{
>>          unsigned long curr_pc;
>>          larch_inst inst;
>>          enum emulation_result er = EMULATE_DONE;
>> @@ -224,21 +251,8 @@ static int kvm_trap_handle_gspr(struct kvm_vcpu *vcpu)
>>          er = EMULATE_FAIL;
>>          switch (((inst.word >> 24) & 0xff)) {
>>          case 0x0: /* CPUCFG GSPR */
>> -               if (inst.reg2_format.opcode == 0x1B) {
>> -                       rd = inst.reg2_format.rd;
>> -                       rj = inst.reg2_format.rj;
>> -                       ++vcpu->stat.cpucfg_exits;
>> -                       index = vcpu->arch.gprs[rj];
>> -                       er = EMULATE_DONE;
>> -                       /*
>> -                        * By LoongArch Reference Manual 2.2.10.5
>> -                        * return value is 0 for undefined cpucfg index
>> -                        */
>> -                       if (index < KVM_MAX_CPUCFG_REGS)
>> -                               vcpu->arch.gprs[rd] = vcpu->arch.cpucfg[index];
>> -                       else
>> -                               vcpu->arch.gprs[rd] = 0;
>> -               }
>> +               if (inst.reg2_format.opcode == cpucfg_op)
>> +                       er = kvm_emu_cpucfg(vcpu, inst);
>>                  break;
>>          case 0x4: /* CSR{RD,WR,XCHG} GSPR */
>>                  er = kvm_handle_csr(vcpu, inst);
>> --
>> 2.39.3
>>