Re: [PATCH v2 1/5] LoongArch: KVM: Add vmid support for stage2 MMU

On 2026/8/6 下午8:20, Huacai Chen wrote:
> Hi, Bibo,
> 
> On Thu, Aug 6, 2026 at 10:14 AM Bibo Mao <[email protected]> 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 unchanged, so that TLB entries
>> for stage2 MMU is valid still. Also vmid index of the whole VM machine
>> is the same on one physical CPU, all vCPUs on the VM can share the
>> same vmid index on one physical CPU.
>>
>> Here hw vmid index is added and it keeps the same with hw vpid still.
> HW VPID means GSTAT.GID, HW VMID means GTLBC.TGID, right? It is useful
> to describe it in the commit message.
yes, it is right.
Will add this description in the commit message.
> 
> 
>>
>> Signed-off-by: Bibo Mao <[email protected]>
>> ---
>>   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..78f97dea124d 100644
>> --- a/arch/loongarch/include/asm/kvm_host.h
>> +++ b/arch/loongarch/include/asm/kvm_host.h
>> @@ -232,6 +232,9 @@ struct kvm_vcpu_arch {
>>          /* Cache for pages needed inside spinlock regions */
>>          struct kvm_mmu_memory_cache mmu_page_cache;
>>
>> +       /* hw vmid info for guest VM */
>> +       unsigned long hw_vmid;
> Since this is only used to write GCNTC.TGID, simply rename it to tgid
> can eliminate confusion.
ok, tgid sounds good to me.
> 
>> +
>>          /* vcpu's vpid */
>>          u64 vpid;
>>          gpa_t flush_gpa;
>> diff --git a/arch/loongarch/kernel/asm-offsets.c b/arch/loongarch/kernel/asm-offsets.c
>> index 1b861cbc5e10..065ced1f3c1f 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, hw_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..401c84f38e8c 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.hw_vmid = vcpu->arch.vpid & vpid_mask;
> Merge Patch#1 and Patch#2, then we can avoid adding this line and then
> remove it immediately.
will merge Patch#1 and Patch#2 in next version.

Regards
Bibo Mao
> 
> 
>>   }
>>
>>   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..b25847aab968 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.hw_vmid << CSR_GSTAT_GID_SHIFT) & CSR_GSTAT_GID;
>> +       invtlb(INVTLB_GID_ADDR, vmid, gpa);
>>   }
>> --
>> 2.39.3
>>