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Subject: Re: [PATCH v4 6/6] LoongArch: Add pv ipi support on LoongArch system
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: <20240201031950.3225626-1-maobibo@loongson.cn>
 <20240201031950.3225626-7-maobibo@loongson.cn>
 <CAAhV-H6RTUWF9cUwCGhLxfaeSqAp+a4uw8fy8brGT9LumU5tdA@mail.gmail.com>
 <a52a9cfe-0c8a-dd10-2d5c-eb2817deb3da@loongson.cn>
 <CAAhV-H4gq=dpvkpRGEa--MtQ3-bAXgehvWQxK3jQOwZEU1Gtag@mail.gmail.com>
From: maobibo <maobibo@loongson.cn>
Message-ID: <03f855ff-0eb7-b4ea-f5ec-4efb0d711f45@loongson.cn>
Date: Mon, 19 Feb 2024 15:37:46 +0800
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On 2024/2/19 下午3:16, Huacai Chen wrote:
> On Mon, Feb 19, 2024 at 12:18 PM maobibo <maobibo@loongson.cn> wrote:
>>
>>
>>
>> On 2024/2/19 上午10:45, Huacai Chen wrote:
>>> Hi, Bibo,
>>>
>>> On Thu, Feb 1, 2024 at 11:20 AM Bibo Mao <maobibo@loongson.cn> wrote:
>>>>
>>>> On LoongArch system, ipi hw uses iocsr registers, there is one iocsr
>>>> register access on ipi sending, and two iocsr access on ipi receiving
>>>> which is ipi interrupt handler. On VM mode all iocsr registers
>>>> accessing will cause VM to trap into hypervisor. So with ipi hw
>>>> notification once there will be three times of trap.
>>>>
>>>> This patch adds pv ipi support for VM, hypercall instruction is used
>>>> to ipi sender, and hypervisor will inject SWI on the VM. During SWI
>>>> interrupt handler, only estat CSR register is written to clear irq.
>>>> Estat CSR register access will not trap into hypervisor. So with pv ipi
>>>> supported, pv ipi sender will trap into hypervsor one time, pv ipi
>>>> revicer will not trap, there is only one time of trap.
>>>>
>>>> Also this patch adds ipi multicast support, the method is similar with
>>>> x86. With ipi multicast support, ipi notification can be sent to at most
>>>> 128 vcpus at one time. It reduces trap times into hypervisor greatly.
>>>>
>>>> Signed-off-by: Bibo Mao <maobibo@loongson.cn>
>>>> ---
>>>>    arch/loongarch/include/asm/hardirq.h   |   1 +
>>>>    arch/loongarch/include/asm/kvm_host.h  |   1 +
>>>>    arch/loongarch/include/asm/kvm_para.h  | 124 +++++++++++++++++++++++++
>>>>    arch/loongarch/include/asm/loongarch.h |   1 +
>>>>    arch/loongarch/kernel/irq.c            |   2 +-
>>>>    arch/loongarch/kernel/paravirt.c       | 113 ++++++++++++++++++++++
>>>>    arch/loongarch/kernel/smp.c            |   2 +-
>>>>    arch/loongarch/kvm/exit.c              |  73 ++++++++++++++-
>>>>    arch/loongarch/kvm/vcpu.c              |   1 +
>>>>    9 files changed, 314 insertions(+), 4 deletions(-)
>>>>
>>>> diff --git a/arch/loongarch/include/asm/hardirq.h b/arch/loongarch/include/asm/hardirq.h
>>>> index 9f0038e19c7f..8a611843c1f0 100644
>>>> --- a/arch/loongarch/include/asm/hardirq.h
>>>> +++ b/arch/loongarch/include/asm/hardirq.h
>>>> @@ -21,6 +21,7 @@ enum ipi_msg_type {
>>>>    typedef struct {
>>>>           unsigned int ipi_irqs[NR_IPI];
>>>>           unsigned int __softirq_pending;
>>>> +       atomic_t messages ____cacheline_aligned_in_smp;
>>> Do we really need atomic_t? A plain "unsigned int" can reduce cost
>>> significantly.
>> For IPI, there are multiple senders and one receiver, the sender uses
>> atomic_fetch_or(action, &info->messages) and the receiver uses
>> atomic_xchg(&info->messages, 0) to clear message.
>>
>> There needs sync mechanism between senders and receiver, atomic is the
>> most simple method.
> At least from receiver side, the native IPI doesn't need atomic for
> read and clear:
> static u32 ipi_read_clear(int cpu)
> {
>          u32 action;
> 
>          /* Load the ipi register to figure out what we're supposed to do */
>          action = iocsr_read32(LOONGARCH_IOCSR_IPI_STATUS);
>          /* Clear the ipi register to clear the interrupt */
>          iocsr_write32(action, LOONGARCH_IOCSR_IPI_CLEAR);
>          wbflush();
It is because on physical hardware it is two IOCSR registers and also 
there is no method to use atomic read and clear method for IOCSR registers.

However if ipi message is stored on ddr memory, atomic read/clear can 
used. Your can compare price of one iocsr_read32 + one iocsr_write32 + 
wbflush with one atomic_xchg(&info->messages, 0)

Regards
Bibo Mao
> 
>          return action;
> }
> 
>>>
>>>>    } ____cacheline_aligned irq_cpustat_t;
>>>>
>>>>    DECLARE_PER_CPU_SHARED_ALIGNED(irq_cpustat_t, irq_stat);
>>>> diff --git a/arch/loongarch/include/asm/kvm_host.h b/arch/loongarch/include/asm/kvm_host.h
>>>> index 57399d7cf8b7..1bf927e2bfac 100644
>>>> --- a/arch/loongarch/include/asm/kvm_host.h
>>>> +++ b/arch/loongarch/include/asm/kvm_host.h
>>>> @@ -43,6 +43,7 @@ struct kvm_vcpu_stat {
>>>>           u64 idle_exits;
>>>>           u64 cpucfg_exits;
>>>>           u64 signal_exits;
>>>> +       u64 hvcl_exits;
>>> hypercall_exits is better.
>> yeap, hypercall_exits is better, will fix in next version.
>>>
>>>>    };
>>>>
>>>>    #define KVM_MEM_HUGEPAGE_CAPABLE       (1UL << 0)
>>>> diff --git a/arch/loongarch/include/asm/kvm_para.h b/arch/loongarch/include/asm/kvm_para.h
>>>> index 41200e922a82..a25a84e372b9 100644
>>>> --- a/arch/loongarch/include/asm/kvm_para.h
>>>> +++ b/arch/loongarch/include/asm/kvm_para.h
>>>> @@ -9,6 +9,10 @@
>>>>    #define HYPERVISOR_VENDOR_SHIFT                8
>>>>    #define HYPERCALL_CODE(vendor, code)   ((vendor << HYPERVISOR_VENDOR_SHIFT) + code)
>>>>
>>>> +#define KVM_HC_CODE_SERVICE            0
>>>> +#define KVM_HC_SERVICE                 HYPERCALL_CODE(HYPERVISOR_KVM, KVM_HC_CODE_SERVICE)
>>>> +#define  KVM_HC_FUNC_IPI               1
>>> Change HC to HCALL is better.
>> will modify in next version.
>>>
>>>> +
>>>>    /*
>>>>     * LoongArch hypcall return code
>>>>     */
>>>> @@ -16,6 +20,126 @@
>>>>    #define KVM_HC_INVALID_CODE            -1UL
>>>>    #define KVM_HC_INVALID_PARAMETER       -2UL
>>>>
>>>> +/*
>>>> + * Hypercalls interface for KVM hypervisor
>>>> + *
>>>> + * a0: function identifier
>>>> + * a1-a6: args
>>>> + * Return value will be placed in v0.
>>>> + * Up to 6 arguments are passed in a1, a2, a3, a4, a5, a6.
>>>> + */
>>>> +static __always_inline long kvm_hypercall(u64 fid)
>>>> +{
>>>> +       register long ret asm("v0");
>>>> +       register unsigned long fun asm("a0") = fid;
>>>> +
>>>> +       __asm__ __volatile__(
>>>> +               "hvcl "__stringify(KVM_HC_SERVICE)
>>>> +               : "=r" (ret)
>>>> +               : "r" (fun)
>>>> +               : "memory"
>>>> +               );
>>>> +
>>>> +       return ret;
>>>> +}
>>>> +
>>>> +static __always_inline long kvm_hypercall1(u64 fid, unsigned long arg0)
>>>> +{
>>>> +       register long ret asm("v0");
>>>> +       register unsigned long fun asm("a0") = fid;
>>>> +       register unsigned long a1  asm("a1") = arg0;
>>>> +
>>>> +       __asm__ __volatile__(
>>>> +               "hvcl "__stringify(KVM_HC_SERVICE)
>>>> +               : "=r" (ret)
>>>> +               : "r" (fun), "r" (a1)
>>>> +               : "memory"
>>>> +               );
>>>> +
>>>> +       return ret;
>>>> +}
>>>> +
>>>> +static __always_inline long kvm_hypercall2(u64 fid,
>>>> +               unsigned long arg0, unsigned long arg1)
>>>> +{
>>>> +       register long ret asm("v0");
>>>> +       register unsigned long fun asm("a0") = fid;
>>>> +       register unsigned long a1  asm("a1") = arg0;
>>>> +       register unsigned long a2  asm("a2") = arg1;
>>>> +
>>>> +       __asm__ __volatile__(
>>>> +                       "hvcl "__stringify(KVM_HC_SERVICE)
>>>> +                       : "=r" (ret)
>>>> +                       : "r" (fun), "r" (a1), "r" (a2)
>>>> +                       : "memory"
>>>> +                       );
>>>> +
>>>> +       return ret;
>>>> +}
>>>> +
>>>> +static __always_inline long kvm_hypercall3(u64 fid,
>>>> +       unsigned long arg0, unsigned long arg1, unsigned long arg2)
>>>> +{
>>>> +       register long ret asm("v0");
>>>> +       register unsigned long fun asm("a0") = fid;
>>>> +       register unsigned long a1  asm("a1") = arg0;
>>>> +       register unsigned long a2  asm("a2") = arg1;
>>>> +       register unsigned long a3  asm("a3") = arg2;
>>>> +
>>>> +       __asm__ __volatile__(
>>>> +               "hvcl "__stringify(KVM_HC_SERVICE)
>>>> +               : "=r" (ret)
>>>> +               : "r" (fun), "r" (a1), "r" (a2), "r" (a3)
>>>> +               : "memory"
>>>> +               );
>>>> +
>>>> +       return ret;
>>>> +}
>>>> +
>>>> +static __always_inline long kvm_hypercall4(u64 fid,
>>>> +               unsigned long arg0, unsigned long arg1, unsigned long arg2,
>>>> +               unsigned long arg3)
>>>> +{
>>>> +       register long ret asm("v0");
>>>> +       register unsigned long fun asm("a0") = fid;
>>>> +       register unsigned long a1  asm("a1") = arg0;
>>>> +       register unsigned long a2  asm("a2") = arg1;
>>>> +       register unsigned long a3  asm("a3") = arg2;
>>>> +       register unsigned long a4  asm("a4") = arg3;
>>>> +
>>>> +       __asm__ __volatile__(
>>>> +               "hvcl "__stringify(KVM_HC_SERVICE)
>>>> +               : "=r" (ret)
>>>> +               : "r"(fun), "r" (a1), "r" (a2), "r" (a3), "r" (a4)
>>>> +               : "memory"
>>>> +               );
>>>> +
>>>> +       return ret;
>>>> +}
>>>> +
>>>> +static __always_inline long kvm_hypercall5(u64 fid,
>>>> +               unsigned long arg0, unsigned long arg1, unsigned long arg2,
>>>> +               unsigned long arg3, unsigned long arg4)
>>>> +{
>>>> +       register long ret asm("v0");
>>>> +       register unsigned long fun asm("a0") = fid;
>>>> +       register unsigned long a1  asm("a1") = arg0;
>>>> +       register unsigned long a2  asm("a2") = arg1;
>>>> +       register unsigned long a3  asm("a3") = arg2;
>>>> +       register unsigned long a4  asm("a4") = arg3;
>>>> +       register unsigned long a5  asm("a5") = arg4;
>>>> +
>>>> +       __asm__ __volatile__(
>>>> +               "hvcl "__stringify(KVM_HC_SERVICE)
>>>> +               : "=r" (ret)
>>>> +               : "r"(fun), "r" (a1), "r" (a2), "r" (a3), "r" (a4), "r" (a5)
>>>> +               : "memory"
>>>> +               );
>>>> +
>>>> +       return ret;
>>>> +}
>>>> +
>>>> +
>>>>    static inline unsigned int kvm_arch_para_features(void)
>>>>    {
>>>>           return 0;
>>>> diff --git a/arch/loongarch/include/asm/loongarch.h b/arch/loongarch/include/asm/loongarch.h
>>>> index a1d22e8b6f94..0ad36704cb4b 100644
>>>> --- a/arch/loongarch/include/asm/loongarch.h
>>>> +++ b/arch/loongarch/include/asm/loongarch.h
>>>> @@ -167,6 +167,7 @@
>>>>    #define CPUCFG_KVM_SIG                 CPUCFG_KVM_BASE
>>>>    #define  KVM_SIGNATURE                 "KVM\0"
>>>>    #define CPUCFG_KVM_FEATURE             (CPUCFG_KVM_BASE + 4)
>>>> +#define  KVM_FEATURE_PV_IPI            BIT(1)
>>>>
>>>>    #ifndef __ASSEMBLY__
>>>>
>>>> diff --git a/arch/loongarch/kernel/irq.c b/arch/loongarch/kernel/irq.c
>>>> index ce36897d1e5a..4863e6c1b739 100644
>>>> --- a/arch/loongarch/kernel/irq.c
>>>> +++ b/arch/loongarch/kernel/irq.c
>>>> @@ -113,5 +113,5 @@ void __init init_IRQ(void)
>>>>                           per_cpu(irq_stack, i), per_cpu(irq_stack, i) + IRQ_STACK_SIZE);
>>>>           }
>>>>
>>>> -       set_csr_ecfg(ECFGF_IP0 | ECFGF_IP1 | ECFGF_IP2 | ECFGF_IPI | ECFGF_PMC);
>>>> +       set_csr_ecfg(ECFGF_SIP0 | ECFGF_IP0 | ECFGF_IP1 | ECFGF_IP2 | ECFGF_IPI | ECFGF_PMC);
>>>>    }
>>>> diff --git a/arch/loongarch/kernel/paravirt.c b/arch/loongarch/kernel/paravirt.c
>>>> index 21d01d05791a..7a8319df401c 100644
>>>> --- a/arch/loongarch/kernel/paravirt.c
>>>> +++ b/arch/loongarch/kernel/paravirt.c
>>>> @@ -1,6 +1,7 @@
>>>>    // SPDX-License-Identifier: GPL-2.0
>>>>    #include <linux/export.h>
>>>>    #include <linux/types.h>
>>>> +#include <linux/interrupt.h>
>>>>    #include <linux/jump_label.h>
>>>>    #include <linux/kvm_para.h>
>>>>    #include <asm/paravirt.h>
>>>> @@ -16,6 +17,104 @@ static u64 native_steal_clock(int cpu)
>>>>
>>>>    DEFINE_STATIC_CALL(pv_steal_clock, native_steal_clock);
>>>>
>>>> +#ifdef CONFIG_SMP
>>>> +static void pv_send_ipi_single(int cpu, unsigned int action)
>>>> +{
>>>> +       unsigned int min, old;
>>>> +       unsigned long bitmap = 0;
>>>> +       irq_cpustat_t *info = &per_cpu(irq_stat, cpu);
>>>> +
>>>> +       action = BIT(action);
>>>> +       old = atomic_fetch_or(action, &info->messages);
>>>> +       if (old == 0) {
>>>> +               min = cpu_logical_map(cpu);
>>>> +               bitmap = 1;
>>>> +               kvm_hypercall3(KVM_HC_FUNC_IPI, bitmap, 0, min);
>>>> +       }
>>>> +}
>>>> +
>>>> +#define KVM_IPI_CLUSTER_SIZE           (2 * BITS_PER_LONG)
>>>> +static void pv_send_ipi_mask(const struct cpumask *mask, unsigned int action)
>>>> +{
>>>> +       unsigned int cpu, i, min = 0, max = 0, old;
>>>> +       __uint128_t bitmap = 0;
>>>> +       irq_cpustat_t *info;
>>>> +
>>>> +       if (cpumask_empty(mask))
>>>> +               return;
>>>> +
>>>> +       action = BIT(action);
>>>> +       for_each_cpu(i, mask) {
>>>> +               info = &per_cpu(irq_stat, i);
>>>> +               old = atomic_fetch_or(action, &info->messages);
>>>> +               if (old)
>>>> +                       continue;
>>>> +
>>>> +               cpu = cpu_logical_map(i);
>>>> +               if (!bitmap) {
>>>> +                       min = max = cpu;
>>>> +               } else if (cpu > min && cpu < min + KVM_IPI_CLUSTER_SIZE) {
>>>> +                       max = cpu > max ? cpu : max;
>>>> +               } else if (cpu < min && (max - cpu) < KVM_IPI_CLUSTER_SIZE) {
>>>> +                       bitmap <<= min - cpu;
>>>> +                       min = cpu;
>>>> +               } else {
>>>> +                       /*
>>>> +                        * Physical cpuid is sorted in ascending order ascend
>>>> +                        * for the next mask calculation, send IPI here
>>>> +                        * directly and skip the remainding cpus
>>>> +                        */
>>>> +                       kvm_hypercall3(KVM_HC_FUNC_IPI, (unsigned long)bitmap,
>>>> +                               (unsigned long)(bitmap >> BITS_PER_LONG), min);
>>>> +                       min = max = cpu;
>>>> +                       bitmap = 0;
>>>> +               }
>>>> +               __set_bit(cpu - min, (unsigned long *)&bitmap);
>>>> +       }
>>>> +
>>>> +       if (bitmap)
>>>> +               kvm_hypercall3(KVM_HC_FUNC_IPI, (unsigned long)bitmap,
>>>> +                               (unsigned long)(bitmap >> BITS_PER_LONG), min);
>>>> +}
>>>> +
>>>> +static irqreturn_t loongson_do_swi(int irq, void *dev)
>>>> +{
>>>> +       irq_cpustat_t *info;
>>>> +       long action;
>>>> +
>>>> +       clear_csr_estat(1 << INT_SWI0);
>>>> +
>>>> +       info = this_cpu_ptr(&irq_stat);
>>>> +       do {
>>>> +               action = atomic_xchg(&info->messages, 0);
>>>> +               if (action & SMP_CALL_FUNCTION) {
>>>> +                       generic_smp_call_function_interrupt();
>>>> +                       info->ipi_irqs[IPI_CALL_FUNCTION]++;
>>>> +               }
>>>> +
>>>> +               if (action & SMP_RESCHEDULE) {
>>>> +                       scheduler_ipi();
>>>> +                       info->ipi_irqs[IPI_RESCHEDULE]++;
>>>> +               }
>>>> +       } while (action);
>>>> +
>>>> +       return IRQ_HANDLED;
>>>> +}
>>>> +
>>>> +static void pv_init_ipi(void)
>>>> +{
>>>> +       int r, swi0;
>>>> +
>>>> +       swi0 = get_percpu_irq(INT_SWI0);
>>>> +       if (swi0 < 0)
>>>> +               panic("SWI0 IRQ mapping failed\n");
>>>> +       irq_set_percpu_devid(swi0);
>>>> +       r = request_percpu_irq(swi0, loongson_do_swi, "SWI0", &irq_stat);
>>>> +       if (r < 0)
>>>> +               panic("SWI0 IRQ request failed\n");
>>>> +}
>>>> +#endif
>>>> +
>>>>    static bool kvm_para_available(void)
>>>>    {
>>>>           static int hypervisor_type;
>>>> @@ -32,10 +131,24 @@ static bool kvm_para_available(void)
>>>>
>>>>    int __init pv_guest_init(void)
>>>>    {
>>>> +       int feature;
>>>> +
>>>>           if (!cpu_has_hypervisor)
>>>>                   return 0;
>>>>           if (!kvm_para_available())
>>>>                   return 0;
>>>>
>>>> +       /*
>>>> +        * check whether KVM hypervisor supports pv_ipi or not
>>>> +        */
>>>> +#ifdef CONFIG_SMP
>>>> +       feature = read_cpucfg(CPUCFG_KVM_FEATURE);
>>> This line can be moved out of CONFIG_SMP, especially features will
>>> increase in future.
>> Good suggestion, will modify in next version.
>>
>> Regards
>> Bibo Mao
>>>
>>> Huacai
>>>
>>>> +       if (feature & KVM_FEATURE_PV_IPI) {
>>>> +               smp_ops.init_ipi                = pv_init_ipi;
>>>> +               smp_ops.send_ipi_single         = pv_send_ipi_single;
>>>> +               smp_ops.send_ipi_mask           = pv_send_ipi_mask;
>>>> +       }
>>>> +#endif
>>>> +
>>>>           return 1;
>>>>    }
>>>> diff --git a/arch/loongarch/kernel/smp.c b/arch/loongarch/kernel/smp.c
>>>> index 3d3ec07d1ec4..d50443879353 100644
>>>> --- a/arch/loongarch/kernel/smp.c
>>>> +++ b/arch/loongarch/kernel/smp.c
>>>> @@ -285,7 +285,7 @@ void loongson_boot_secondary(int cpu, struct task_struct *idle)
>>>>    void loongson_init_secondary(void)
>>>>    {
>>>>           unsigned int cpu = smp_processor_id();
>>>> -       unsigned int imask = ECFGF_IP0 | ECFGF_IP1 | ECFGF_IP2 |
>>>> +       unsigned int imask = ECFGF_SIP0 | ECFGF_IP0 | ECFGF_IP1 | ECFGF_IP2 |
>>>>                                ECFGF_IPI | ECFGF_PMC | ECFGF_TIMER;
>>>>
>>>>           change_csr_ecfg(ECFG0_IM, imask);
>>>> diff --git a/arch/loongarch/kvm/exit.c b/arch/loongarch/kvm/exit.c
>>>> index f4e4df05f578..189b70bad825 100644
>>>> --- a/arch/loongarch/kvm/exit.c
>>>> +++ b/arch/loongarch/kvm/exit.c
>>>> @@ -227,6 +227,9 @@ static int kvm_emu_cpucfg(struct kvm_vcpu *vcpu, larch_inst inst)
>>>>           case CPUCFG_KVM_SIG:
>>>>                   vcpu->arch.gprs[rd] = *(unsigned int *)KVM_SIGNATURE;
>>>>                   break;
>>>> +       case CPUCFG_KVM_FEATURE:
>>>> +               vcpu->arch.gprs[rd] = KVM_FEATURE_PV_IPI;
>>>> +               break;
>>>>           default:
>>>>                   vcpu->arch.gprs[rd] = 0;
>>>>                   break;
>>>> @@ -699,12 +702,78 @@ static int kvm_handle_lasx_disabled(struct kvm_vcpu *vcpu)
>>>>           return RESUME_GUEST;
>>>>    }
>>>>
>>>> +static int kvm_pv_send_ipi(struct kvm_vcpu *vcpu)
>>>> +{
>>>> +       unsigned long ipi_bitmap;
>>>> +       unsigned int min, cpu, i;
>>>> +       struct kvm_vcpu *dest;
>>>> +
>>>> +       min = vcpu->arch.gprs[LOONGARCH_GPR_A3];
>>>> +       for (i = 0; i < 2; i++) {
>>>> +               ipi_bitmap = vcpu->arch.gprs[LOONGARCH_GPR_A1 + i];
>>>> +               if (!ipi_bitmap)
>>>> +                       continue;
>>>> +
>>>> +               cpu = find_first_bit((void *)&ipi_bitmap, BITS_PER_LONG);
>>>> +               while (cpu < BITS_PER_LONG) {
>>>> +                       dest = kvm_get_vcpu_by_cpuid(vcpu->kvm, cpu + min);
>>>> +                       cpu = find_next_bit((void *)&ipi_bitmap, BITS_PER_LONG,
>>>> +                                               cpu + 1);
>>>> +                       if (!dest)
>>>> +                               continue;
>>>> +
>>>> +                       /*
>>>> +                        * Send SWI0 to dest vcpu to emulate IPI interrupt
>>>> +                        */
>>>> +                       kvm_queue_irq(dest, INT_SWI0);
>>>> +                       kvm_vcpu_kick(dest);
>>>> +               }
>>>> +       }
>>>> +
>>>> +       return 0;
>>>> +}
>>>> +
>>>> +/*
>>>> + * hypcall emulation always return to guest, Caller should check retval.
>>>> + */
>>>> +static void kvm_handle_pv_hcall(struct kvm_vcpu *vcpu)
>>> Rename to kvm_handle_hypecall_service() is better.
>>>
>>>
>>> Huacai
>>>> +{
>>>> +       unsigned long func = vcpu->arch.gprs[LOONGARCH_GPR_A0];
>>>> +       long ret;
>>>> +
>>>> +       switch (func) {
>>>> +       case KVM_HC_FUNC_IPI:
>>>> +               kvm_pv_send_ipi(vcpu);
>>>> +               ret = KVM_HC_STATUS_SUCCESS;
>>>> +               break;
>>>> +       default:
>>>> +               ret = KVM_HC_INVALID_CODE;
>>>> +               break;
>>>> +       };
>>>> +
>>>> +       vcpu->arch.gprs[LOONGARCH_GPR_A0] = ret;
>>>> +}
>>>> +
>>>>    static int kvm_handle_hypcall(struct kvm_vcpu *vcpu)
>>>>    {
>>>> +       larch_inst inst;
>>>> +       unsigned int code;
>>>> +
>>>> +       inst.word = vcpu->arch.badi;
>>>> +       code = inst.reg0i15_format.immediate;
>>>>           update_pc(&vcpu->arch);
>>>>
>>>> -       /* Treat it as noop intruction, only set return value */
>>>> -       vcpu->arch.gprs[LOONGARCH_GPR_A0] = KVM_HC_INVALID_CODE;
>>>> +       switch (code) {
>>>> +       case KVM_HC_SERVICE:
>>>> +               vcpu->stat.hvcl_exits++;
>>>> +               kvm_handle_pv_hcall(vcpu);
>>>> +               break;
>>>> +       default:
>>>> +               /* Treat it as noop intruction, only set return value */
>>>> +               vcpu->arch.gprs[LOONGARCH_GPR_A0] = KVM_HC_INVALID_CODE;
>>>> +               break;
>>>> +       }
>>>> +
>>>>           return RESUME_GUEST;
>>>>    }
>>>>
>>>> diff --git a/arch/loongarch/kvm/vcpu.c b/arch/loongarch/kvm/vcpu.c
>>>> index 97ca9c7160e6..80e05ba9b48d 100644
>>>> --- a/arch/loongarch/kvm/vcpu.c
>>>> +++ b/arch/loongarch/kvm/vcpu.c
>>>> @@ -19,6 +19,7 @@ const struct _kvm_stats_desc kvm_vcpu_stats_desc[] = {
>>>>           STATS_DESC_COUNTER(VCPU, idle_exits),
>>>>           STATS_DESC_COUNTER(VCPU, cpucfg_exits),
>>>>           STATS_DESC_COUNTER(VCPU, signal_exits),
>>>> +       STATS_DESC_COUNTER(VCPU, hvcl_exits)
>>>>    };
>>>>
>>>>    const struct kvm_stats_header kvm_vcpu_stats_header = {
>>>> --
>>>> 2.39.3
>>>>
>>