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Subject: Re: [PATCH v8 4/6] LoongArch: KVM: Add vcpu search support from
 physical cpuid
To: Huacai Chen <chenhuacai@kernel.org>
Cc: Tianrui Zhao <zhaotianrui@loongson.cn>, Juergen Gross <jgross@suse.com>,
 Paolo Bonzini <pbonzini@redhat.com>, Jonathan Corbet <corbet@lwn.net>,
 loongarch@lists.linux.dev, linux-kernel@vger.kernel.org,
 virtualization@lists.linux.dev, kvm@vger.kernel.org
References: <20240428100518.1642324-1-maobibo@loongson.cn>
 <20240428100518.1642324-5-maobibo@loongson.cn>
 <CAAhV-H6kBO_RTTHoLfKdAtLO1Aqb0KmAJ6wn0wZrvbCkzMszDQ@mail.gmail.com>
 <7335dcde-1b3a-1260-ac62-d2d9fcbd6a78@loongson.cn>
 <CAAhV-H5WJ0o3bJZBq2zx7ejjFkFwYVTyVJEzJuAHEs+uMg-sxw@mail.gmail.com>
 <b10b46ce-8219-8863-470f-9bfa173b22b0@loongson.cn>
 <CAAhV-H7fbrOXTtSwBmR3kyTW7yhsifycjynky4HPrUJiS9s=cg@mail.gmail.com>
From: maobibo <maobibo@loongson.cn>
Message-ID: <540aa8dd-eada-1f77-0a20-38196fb5472a@loongson.cn>
Date: Mon, 6 May 2024 17:35:07 +0800
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On 2024/5/6 下午4:59, Huacai Chen wrote:
> On Mon, May 6, 2024 at 4:18 PM maobibo <maobibo@loongson.cn> wrote:
>>
>>
>>
>> On 2024/5/6 下午3:06, Huacai Chen wrote:
>>> Hi, Bibo,
>>>
>>> On Mon, May 6, 2024 at 2:36 PM maobibo <maobibo@loongson.cn> wrote:
>>>>
>>>>
>>>>
>>>> On 2024/5/6 上午9:49, Huacai Chen wrote:
>>>>> Hi, Bibo,
>>>>>
>>>>> On Sun, Apr 28, 2024 at 6:05 PM Bibo Mao <maobibo@loongson.cn> wrote:
>>>>>>
>>>>>> Physical cpuid is used for interrupt routing for irqchips such as
>>>>>> ipi/msi/extioi interrupt controller. And physical cpuid is stored
>>>>>> at CSR register LOONGARCH_CSR_CPUID, it can not be changed once vcpu
>>>>>> is created and physical cpuid of two vcpus cannot be the same.
>>>>>>
>>>>>> Different irqchips have different size declaration about physical cpuid,
>>>>>> max cpuid value for CSR LOONGARCH_CSR_CPUID on 3A5000 is 512, max cpuid
>>>>>> supported by IPI hardware is 1024, 256 for extioi irqchip, and 65536
>>>>>> for MSI irqchip.
>>>>>>
>>>>>> The smallest value from all interrupt controllers is selected now,
>>>>>> and the max cpuid size is defines as 256 by KVM which comes from
>>>>>> extioi irqchip.
>>>>>>
>>>>>> Signed-off-by: Bibo Mao <maobibo@loongson.cn>
>>>>>> ---
>>>>>>     arch/loongarch/include/asm/kvm_host.h | 26 ++++++++
>>>>>>     arch/loongarch/include/asm/kvm_vcpu.h |  1 +
>>>>>>     arch/loongarch/kvm/vcpu.c             | 93 ++++++++++++++++++++++++++-
>>>>>>     arch/loongarch/kvm/vm.c               | 11 ++++
>>>>>>     4 files changed, 130 insertions(+), 1 deletion(-)
>>>>>>
>>>>>> diff --git a/arch/loongarch/include/asm/kvm_host.h b/arch/loongarch/include/asm/kvm_host.h
>>>>>> index 2d62f7b0d377..3ba16ef1fe69 100644
>>>>>> --- a/arch/loongarch/include/asm/kvm_host.h
>>>>>> +++ b/arch/loongarch/include/asm/kvm_host.h
>>>>>> @@ -64,6 +64,30 @@ struct kvm_world_switch {
>>>>>>
>>>>>>     #define MAX_PGTABLE_LEVELS     4
>>>>>>
>>>>>> +/*
>>>>>> + * Physical cpu id is used for interrupt routing, there are different
>>>>>> + * definitions about physical cpuid on different hardwares.
>>>>>> + *  For LOONGARCH_CSR_CPUID register, max cpuid size if 512
>>>>>> + *  For IPI HW, max dest CPUID size 1024
>>>>>> + *  For extioi interrupt controller, max dest CPUID size is 256
>>>>>> + *  For MSI interrupt controller, max supported CPUID size is 65536
>>>>>> + *
>>>>>> + * Currently max CPUID is defined as 256 for KVM hypervisor, in future
>>>>>> + * it will be expanded to 4096, including 16 packages at most. And every
>>>>>> + * package supports at most 256 vcpus
>>>>>> + */
>>>>>> +#define KVM_MAX_PHYID          256
>>>>>> +
>>>>>> +struct kvm_phyid_info {
>>>>>> +       struct kvm_vcpu *vcpu;
>>>>>> +       bool            enabled;
>>>>>> +};
>>>>>> +
>>>>>> +struct kvm_phyid_map {
>>>>>> +       int max_phyid;
>>>>>> +       struct kvm_phyid_info phys_map[KVM_MAX_PHYID];
>>>>>> +};
>>>>>> +
>>>>>>     struct kvm_arch {
>>>>>>            /* Guest physical mm */
>>>>>>            kvm_pte_t *pgd;
>>>>>> @@ -71,6 +95,8 @@ struct kvm_arch {
>>>>>>            unsigned long invalid_ptes[MAX_PGTABLE_LEVELS];
>>>>>>            unsigned int  pte_shifts[MAX_PGTABLE_LEVELS];
>>>>>>            unsigned int  root_level;
>>>>>> +       spinlock_t    phyid_map_lock;
>>>>>> +       struct kvm_phyid_map  *phyid_map;
>>>>>>
>>>>>>            s64 time_offset;
>>>>>>            struct kvm_context __percpu *vmcs;
>>>>>> diff --git a/arch/loongarch/include/asm/kvm_vcpu.h b/arch/loongarch/include/asm/kvm_vcpu.h
>>>>>> index 0cb4fdb8a9b5..9f53950959da 100644
>>>>>> --- a/arch/loongarch/include/asm/kvm_vcpu.h
>>>>>> +++ b/arch/loongarch/include/asm/kvm_vcpu.h
>>>>>> @@ -81,6 +81,7 @@ void kvm_save_timer(struct kvm_vcpu *vcpu);
>>>>>>     void kvm_restore_timer(struct kvm_vcpu *vcpu);
>>>>>>
>>>>>>     int kvm_vcpu_ioctl_interrupt(struct kvm_vcpu *vcpu, struct kvm_interrupt *irq);
>>>>>> +struct kvm_vcpu *kvm_get_vcpu_by_cpuid(struct kvm *kvm, int cpuid);
>>>>>>
>>>>>>     /*
>>>>>>      * Loongarch KVM guest interrupt handling
>>>>>> diff --git a/arch/loongarch/kvm/vcpu.c b/arch/loongarch/kvm/vcpu.c
>>>>>> index 3a8779065f73..b633fd28b8db 100644
>>>>>> --- a/arch/loongarch/kvm/vcpu.c
>>>>>> +++ b/arch/loongarch/kvm/vcpu.c
>>>>>> @@ -274,6 +274,95 @@ static int _kvm_getcsr(struct kvm_vcpu *vcpu, unsigned int id, u64 *val)
>>>>>>            return 0;
>>>>>>     }
>>>>>>
>>>>>> +static inline int kvm_set_cpuid(struct kvm_vcpu *vcpu, u64 val)
>>>>>> +{
>>>>>> +       int cpuid;
>>>>>> +       struct loongarch_csrs *csr = vcpu->arch.csr;
>>>>>> +       struct kvm_phyid_map  *map;
>>>>>> +
>>>>>> +       if (val >= KVM_MAX_PHYID)
>>>>>> +               return -EINVAL;
>>>>>> +
>>>>>> +       cpuid = kvm_read_sw_gcsr(csr, LOONGARCH_CSR_ESTAT);
>>>>>> +       map = vcpu->kvm->arch.phyid_map;
>>>>>> +       spin_lock(&vcpu->kvm->arch.phyid_map_lock);
>>>>>> +       if (map->phys_map[cpuid].enabled) {
>>>>>> +               /*
>>>>>> +                * Cpuid is already set before
>>>>>> +                * Forbid changing different cpuid at runtime
>>>>>> +                */
>>>>>> +               if (cpuid != val) {
>>>>>> +                       /*
>>>>>> +                        * Cpuid 0 is initial value for vcpu, maybe invalid
>>>>>> +                        * unset value for vcpu
>>>>>> +                        */
>>>>>> +                       if (cpuid) {
>>>>>> +                               spin_unlock(&vcpu->kvm->arch.phyid_map_lock);
>>>>>> +                               return -EINVAL;
>>>>>> +                       }
>>>>>> +               } else {
>>>>>> +                        /* Discard duplicated cpuid set */
>>>>>> +                       spin_unlock(&vcpu->kvm->arch.phyid_map_lock);
>>>>>> +                       return 0;
>>>>>> +               }
>>>>>> +       }
>>>>> I have changed the logic and comments when I apply, you can double
>>>>> check whether it is correct.
>>>> I checkout the latest version, the modification in function
>>>> kvm_set_cpuid() is good for me.
>>> Now the modified version is like this:
>>>
>>> + if (map->phys_map[cpuid].enabled) {
>>> + /* Discard duplicated CPUID set operation */
>>> + if (cpuid == val) {
>>> + spin_unlock(&vcpu->kvm->arch.phyid_map_lock);
>>> + return 0;
>>> + }
>>> +
>>> + /*
>>> + * CPUID is already set before
>>> + * Forbid changing different CPUID at runtime
>>> + * But CPUID 0 is the initial value for vcpu, so allow
>>> + * changing from 0 to others
>>> + */
>>> + if (cpuid) {
>>> + spin_unlock(&vcpu->kvm->arch.phyid_map_lock);
>>> + return -EINVAL;
>>> + }
>>> + }
>>> But I still doubt whether we should allow changing from 0 to others
>>> while map->phys_map[cpuid].enabled is 1.
>> It is necessary since the default sw cpuid is zero :-( And we can
>> optimize it in later, such as set INVALID cpuid in function
>> kvm_arch_vcpu_create() and logic will be simple in function kvm_set_cpuid().
> In my opinion, if a vcpu with a uninitialized default physid=0, then
> map->phys_map[cpuid].enabled should be 0, then code won't come here.
> And if a vcpu with a real physid=0, then map->phys_map[cpuid].enabled
> is 1, but we shouldn't allow it to change physid in this case.
yes, that is actually a problem.

vcpu0 firstly set physid=0, and vcpu0 set physid=1 again is not allowed.
vcpu0 firstly set physid=0, and vcpu1 set physid=1 is allowed.


> 
> Huacai
> 
>>
>> Regards
>> Bibo Mao
>>
>>>
>>> Huacai
>>>
>>>>>
>>>>>> +
>>>>>> +       if (map->phys_map[val].enabled) {
>>>>>> +               /*
>>>>>> +                * New cpuid is already set with other vcpu
>>>>>> +                * Forbid sharing the same cpuid between different vcpus
>>>>>> +                */
>>>>>> +               if (map->phys_map[val].vcpu != vcpu) {
>>>>>> +                       spin_unlock(&vcpu->kvm->arch.phyid_map_lock);
>>>>>> +                       return -EINVAL;
>>>>>> +               }
>>>>>> +
>>>>>> +               /* Discard duplicated cpuid set operation*/
>>>>>> +               spin_unlock(&vcpu->kvm->arch.phyid_map_lock);
>>>>>> +               return 0;
>>>>>> +       }
>>>>>> +
>>>>>> +       kvm_write_sw_gcsr(csr, LOONGARCH_CSR_CPUID, val);
>>>>>> +       map->phys_map[val].enabled      = true;
>>>>>> +       map->phys_map[val].vcpu         = vcpu;
>>>>>> +       if (map->max_phyid < val)
>>>>>> +               map->max_phyid = val;
>>>>>> +       spin_unlock(&vcpu->kvm->arch.phyid_map_lock);
>>>>>> +       return 0;
>>>>>> +}
>>>>>> +
>>>>>> +struct kvm_vcpu *kvm_get_vcpu_by_cpuid(struct kvm *kvm, int cpuid)
>>>>>> +{
>>>>>> +       struct kvm_phyid_map  *map;
>>>>>> +
>>>>>> +       if (cpuid >= KVM_MAX_PHYID)
>>>>>> +               return NULL;
>>>>>> +
>>>>>> +       map = kvm->arch.phyid_map;
>>>>>> +       if (map->phys_map[cpuid].enabled)
>>>>>> +               return map->phys_map[cpuid].vcpu;
>>>>>> +
>>>>>> +       return NULL;
>>>>>> +}
>>>>>> +
>>>>>> +static inline void kvm_drop_cpuid(struct kvm_vcpu *vcpu)
>>>>>> +{
>>>>>> +       int cpuid;
>>>>>> +       struct loongarch_csrs *csr = vcpu->arch.csr;
>>>>>> +       struct kvm_phyid_map  *map;
>>>>>> +
>>>>>> +       map = vcpu->kvm->arch.phyid_map;
>>>>>> +       cpuid = kvm_read_sw_gcsr(csr, LOONGARCH_CSR_ESTAT);
>>>>>> +       if (cpuid >= KVM_MAX_PHYID)
>>>>>> +               return;
>>>>>> +
>>>>>> +       if (map->phys_map[cpuid].enabled) {
>>>>>> +               map->phys_map[cpuid].vcpu = NULL;
>>>>>> +               map->phys_map[cpuid].enabled = false;
>>>>>> +               kvm_write_sw_gcsr(csr, LOONGARCH_CSR_CPUID, 0);
>>>>>> +       }
>>>>>> +}
>>>>> While kvm_set_cpuid() is protected by a spinlock, do kvm_drop_cpuid()
>>>>> and kvm_get_vcpu_by_cpuid() also need it?
>>>>>
>>>> It is good to me that spinlock is added in function kvm_drop_cpuid().
>>>> And thinks for the efforts.
>>>>
>>>> Regards
>>>> Bibo Mao
>>>>>> +
>>>>>>     static int _kvm_setcsr(struct kvm_vcpu *vcpu, unsigned int id, u64 val)
>>>>>>     {
>>>>>>            int ret = 0, gintc;
>>>>>> @@ -291,7 +380,8 @@ static int _kvm_setcsr(struct kvm_vcpu *vcpu, unsigned int id, u64 val)
>>>>>>                    kvm_set_sw_gcsr(csr, LOONGARCH_CSR_ESTAT, gintc);
>>>>>>
>>>>>>                    return ret;
>>>>>> -       }
>>>>>> +       } else if (id == LOONGARCH_CSR_CPUID)
>>>>>> +               return kvm_set_cpuid(vcpu, val);
>>>>>>
>>>>>>            kvm_write_sw_gcsr(csr, id, val);
>>>>>>
>>>>>> @@ -943,6 +1033,7 @@ void kvm_arch_vcpu_destroy(struct kvm_vcpu *vcpu)
>>>>>>            hrtimer_cancel(&vcpu->arch.swtimer);
>>>>>>            kvm_mmu_free_memory_cache(&vcpu->arch.mmu_page_cache);
>>>>>>            kfree(vcpu->arch.csr);
>>>>>> +       kvm_drop_cpuid(vcpu);
>>>>> I think this line should be before the above kfree(), otherwise you
>>>>> get a "use after free".
>>>>>
>>>>> Huacai
>>>>>
>>>>>>
>>>>>>            /*
>>>>>>             * If the vCPU is freed and reused as another vCPU, we don't want the
>>>>>> diff --git a/arch/loongarch/kvm/vm.c b/arch/loongarch/kvm/vm.c
>>>>>> index 0a37f6fa8f2d..6006a28653ad 100644
>>>>>> --- a/arch/loongarch/kvm/vm.c
>>>>>> +++ b/arch/loongarch/kvm/vm.c
>>>>>> @@ -30,6 +30,14 @@ int kvm_arch_init_vm(struct kvm *kvm, unsigned long type)
>>>>>>            if (!kvm->arch.pgd)
>>>>>>                    return -ENOMEM;
>>>>>>
>>>>>> +       kvm->arch.phyid_map = kvzalloc(sizeof(struct kvm_phyid_map),
>>>>>> +                               GFP_KERNEL_ACCOUNT);
>>>>>> +       if (!kvm->arch.phyid_map) {
>>>>>> +               free_page((unsigned long)kvm->arch.pgd);
>>>>>> +               kvm->arch.pgd = NULL;
>>>>>> +               return -ENOMEM;
>>>>>> +       }
>>>>>> +
>>>>>>            kvm_init_vmcs(kvm);
>>>>>>            kvm->arch.gpa_size = BIT(cpu_vabits - 1);
>>>>>>            kvm->arch.root_level = CONFIG_PGTABLE_LEVELS - 1;
>>>>>> @@ -44,6 +52,7 @@ int kvm_arch_init_vm(struct kvm *kvm, unsigned long type)
>>>>>>            for (i = 0; i <= kvm->arch.root_level; i++)
>>>>>>                    kvm->arch.pte_shifts[i] = PAGE_SHIFT + i * (PAGE_SHIFT - 3);
>>>>>>
>>>>>> +       spin_lock_init(&kvm->arch.phyid_map_lock);
>>>>>>            return 0;
>>>>>>     }
>>>>>>
>>>>>> @@ -51,7 +60,9 @@ void kvm_arch_destroy_vm(struct kvm *kvm)
>>>>>>     {
>>>>>>            kvm_destroy_vcpus(kvm);
>>>>>>            free_page((unsigned long)kvm->arch.pgd);
>>>>>> +       kvfree(kvm->arch.phyid_map);
>>>>>>            kvm->arch.pgd = NULL;
>>>>>> +       kvm->arch.phyid_map = NULL;
>>>>>>     }
>>>>>>
>>>>>>     int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
>>>>>> --
>>>>>> 2.39.3
>>>>>>
>>>>
>>