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Message-ID: <b6705098-1521-a892-9850-af84acd68674@loongson.cn>
Date: Mon, 26 Feb 2024 10:07:40 +0800
From: maobibo <maobibo@...ngson.cn>
To: Huacai Chen <chenhuacai@...nel.org>
Cc: Tianrui Zhao <zhaotianrui@...ngson.cn>, Juergen Gross <jgross@...e.com>,
Paolo Bonzini <pbonzini@...hat.com>, loongarch@...ts.linux.dev,
linux-kernel@...r.kernel.org, virtualization@...ts.linux.dev,
kvm@...r.kernel.org
Subject: Re: [PATCH v5 3/6] LoongArch: KVM: Add cpucfg area for kvm hypervisor
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@...ngson.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@...ngson.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
>>
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