Re: [PATCH 1/6] LoongArch: KVM: Add vmid support for stage2 MMU

[Bibo Mao <maobibo@loongson.cn>]

On 2026/8/5 上午9:21, Bibo Mao wrote:
> 
> 
> On 2026/8/4 下午10:14, Huacai Chen wrote:
>> On Mon, Aug 3, 2026 at 9:21 AM Bibo Mao <maobibo@loongson.cn> wrote:
>>>
>>>
>>>
>>> On 2026/8/2 下午10:11, Huacai Chen wrote:
>>>> Hi, Bibo,
>>>>
>>>> On Mon, Jul 27, 2026 at 3:29 PM Bibo Mao <maobibo@loongson.cn> wrote:
>>>>>
>>>>> LoongArch KVM hypervisor supports two-level MMU, vpid index is used
>>>>> for stage1 MMU and vmid index is used for stage2 MMU.
>>>>>
>>>>> On 3A5000, vmid must be the same with vpid. On 3A6000 platform vmid
>>>>> may separate from vpid. If vcpu migrate to different physical CPUs,
>>>>> vpid need change however vmid can keep the same with old value. Also
>>>>> vmid index of the while VM machine on physical CPU the same, all vCPUs
>>>>> on the VM can share the same vmid index on one physical CPU.
>>>>>
>>>>> Here vmid index is added and it keeps the same with vpid still.
>>>>>
>>>>> Signed-off-by: Bibo Mao <maobibo@loongson.cn>
>>>>> ---
>>>>>    arch/loongarch/include/asm/kvm_host.h | 3 +++
>>>>>    arch/loongarch/kernel/asm-offsets.c   | 1 +
>>>>>    arch/loongarch/kvm/main.c             | 1 +
>>>>>    arch/loongarch/kvm/switch.S           | 5 ++---
>>>>>    arch/loongarch/kvm/tlb.c              | 5 ++++-
>>>>>    5 files changed, 11 insertions(+), 4 deletions(-)
>>>>>
>>>>> diff --git a/arch/loongarch/include/asm/kvm_host.h 
>>>>> b/arch/loongarch/include/asm/kvm_host.h
>>>>> index 23cfbecebbd7..ec7b0c402385 100644
>>>>> --- a/arch/loongarch/include/asm/kvm_host.h
>>>>> +++ b/arch/loongarch/include/asm/kvm_host.h
>>>>> @@ -189,6 +189,9 @@ struct kvm_vcpu_arch {
>>>>>           unsigned long host_tp;
>>>>>           unsigned long host_pgd;
>>>>>
>>>>> +       /* vmid info for guest VM */
>>>>> +       unsigned long vmid;
>>>> Put it near vpid?
>>> yes, it it better to near vpid. will do this.
>>>>
>>>>> +
>>>>>           /* Host CSRs are used when handling exits from guest */
>>>>>           unsigned long badi;
>>>>>           unsigned long badv;
>>>>> diff --git a/arch/loongarch/kernel/asm-offsets.c 
>>>>> b/arch/loongarch/kernel/asm-offsets.c
>>>>> index 1b861cbc5e10..32ef6adfc8dd 100644
>>>>> --- a/arch/loongarch/kernel/asm-offsets.c
>>>>> +++ b/arch/loongarch/kernel/asm-offsets.c
>>>>> @@ -300,6 +300,7 @@ static void __used output_kvm_defines(void)
>>>>>           OFFSET(KVM_ARCH_HSP, kvm_vcpu_arch, host_sp);
>>>>>           OFFSET(KVM_ARCH_HTP, kvm_vcpu_arch, host_tp);
>>>>>           OFFSET(KVM_ARCH_HPGD, kvm_vcpu_arch, host_pgd);
>>>>> +       OFFSET(KVM_ARCH_VMID, kvm_vcpu_arch, vmid);
>>>>>           OFFSET(KVM_ARCH_KVMPGD, kvm_vcpu_arch, kvm_pgd);
>>>>>           OFFSET(KVM_ARCH_HANDLE_EXIT, kvm_vcpu_arch, handle_exit);
>>>>>           OFFSET(KVM_ARCH_HEENTRY, kvm_vcpu_arch, host_eentry);
>>>>> diff --git a/arch/loongarch/kvm/main.c b/arch/loongarch/kvm/main.c
>>>>> index 3e1005526f4b..6e3e8efa1dc2 100644
>>>>> --- a/arch/loongarch/kvm/main.c
>>>>> +++ b/arch/loongarch/kvm/main.c
>>>>> @@ -223,6 +223,7 @@ static void kvm_update_vpid(struct kvm_vcpu 
>>>>> *vcpu, int cpu)
>>>>>
>>>>>           context->vpid_cache = vpid;
>>>>>           vcpu->arch.vpid = vpid;
>>>>> +       vcpu->arch.vmid = vcpu->arch.vpid & vpid_mask;
>>>>
>>>> I think both vpid and vmid need "& vpid_mask".
>>> vpid used in function kvm_check_vcpuid() includes version information
>>> also. vmid here is hardware id directly used by LOONGARCH_CSR_GTLBC in
>>> arch/loongarch/kvm/switch.S.
>> I'm not sure, but it seems both vpid and vmid have a sw version and a
>> hw version? The hw version will be written into register so its width
>> is limited, while the sw version is 64bit. If I'm right, I think the
> yes, it is.
> 
>> "& vpid_mask" is only used when writing registers, in other places
>> they are full 64bit (in other words, they need the same treatment).
> If vmid includes version, it requires one extra shift operation when 
> writing to real HW in file arch/loongarch/kvm/switch.S.
> -       /* Mix GID and RID */
> -       csrrd           t1, LOONGARCH_CSR_GSTAT
> -       bstrpick.w      t1, t1, CSR_GSTAT_GID_SHIFT_END, 
> CSR_GSTAT_GID_SHIFT
> +       /* Set VMID for gpa --> hpa mapping */
> +       ld.d            t1, a2, KVM_ARCH_VMID
>           csrrd           t0, LOONGARCH_CSR_GTLBC
>           bstrins.w       t0, t1, CSR_GTLBC_TGID_SHIFT_END,
> 
> vpid is per-vcpu and it is represented with *vcpu->arch.vpid*, vmid is 
> per-vm,it is shared by vCPUs and represented with 
> *vcpu->kvm->arch.vmid[cpu]*. Instead arch.vmid is special for HW 
> register writing with LOONGARCH_CSR_GTLBC, if there is misleading, how 
> about renaming it with hw_vmid?
hw_vmid is strange, I am ok with vmid with version information, so that 
the name is clear, one shift assemble code is not too much. Will change 
in the next version.

Regards
Bibo Mao
> 
> Regards
> 
> 
>>
>> Huacai
>>
>>>
>>> Regards
>>> Bibo Mao
>>>>
>>>>
>>>> Huacai
>>>>
>>>>>    }
>>>>>
>>>>>    void kvm_check_vpid(struct kvm_vcpu *vcpu)
>>>>> diff --git a/arch/loongarch/kvm/switch.S b/arch/loongarch/kvm/switch.S
>>>>> index 936e4ae3e408..af972394fd55 100644
>>>>> --- a/arch/loongarch/kvm/switch.S
>>>>> +++ b/arch/loongarch/kvm/switch.S
>>>>> @@ -66,9 +66,8 @@
>>>>>           ld.d    t0, a2, KVM_ARCH_KVMPGD
>>>>>           csrwr   t0, LOONGARCH_CSR_PGDL
>>>>>
>>>>> -       /* Mix GID and RID */
>>>>> -       csrrd           t1, LOONGARCH_CSR_GSTAT
>>>>> -       bstrpick.w      t1, t1, CSR_GSTAT_GID_SHIFT_END, 
>>>>> CSR_GSTAT_GID_SHIFT
>>>>> +       /* Set VMID for gpa --> hpa mapping */
>>>>> +       ld.d            t1, a2, KVM_ARCH_VMID
>>>>>           csrrd           t0, LOONGARCH_CSR_GTLBC
>>>>>           bstrins.w       t0, t1, CSR_GTLBC_TGID_SHIFT_END, 
>>>>> CSR_GTLBC_TGID_SHIFT
>>>>>           csrwr           t0, LOONGARCH_CSR_GTLBC
>>>>> diff --git a/arch/loongarch/kvm/tlb.c b/arch/loongarch/kvm/tlb.c
>>>>> index ebdbe9264e9c..38daf936021d 100644
>>>>> --- a/arch/loongarch/kvm/tlb.c
>>>>> +++ b/arch/loongarch/kvm/tlb.c
>>>>> @@ -23,7 +23,10 @@ void kvm_flush_tlb_all(void)
>>>>>
>>>>>    void kvm_flush_tlb_gpa(struct kvm_vcpu *vcpu, unsigned long gpa)
>>>>>    {
>>>>> +       unsigned int vmid;
>>>>> +
>>>>>           lockdep_assert_irqs_disabled();
>>>>>           gpa &= (PAGE_MASK << 1);
>>>>> -       invtlb(INVTLB_GID_ADDR, read_csr_gstat() & CSR_GSTAT_GID, 
>>>>> gpa);
>>>>> +       vmid = (vcpu->arch.vmid << CSR_GSTAT_GID_SHIFT) & 
>>>>> CSR_GSTAT_GID;
>>>>> +       invtlb(INVTLB_GID_ADDR, vmid, gpa);
>>>>>    }
>>>>> -- 
>>>>> 2.39.3
>>>>>
>>>