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References: <20240428100518.1642324-1-maobibo@loongson.cn> <20240428100518.1642324-5-maobibo@loongson.cn>
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From: Huacai Chen <chenhuacai@kernel.org>
Date: Mon, 6 May 2024 15:06:33 +0800
Message-ID: <CAAhV-H5WJ0o3bJZBq2zx7ejjFkFwYVTyVJEzJuAHEs+uMg-sxw@mail.gmail.com>
Subject: Re: [PATCH v8 4/6] LoongArch: KVM: Add vcpu search support from
 physical cpuid
To: maobibo <maobibo@loongson.cn>
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
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Hi, Bibo,

On Mon, May 6, 2024 at 2:36=E2=80=AFPM maobibo <maobibo@loongson.cn> wrote:
>
>
>
> On 2024/5/6 =E4=B8=8A=E5=8D=889:49, Huacai Chen wrote:
> > Hi, Bibo,
> >
> > On Sun, Apr 28, 2024 at 6:05=E2=80=AFPM 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 cpui=
d,
> >> max cpuid value for CSR LOONGARCH_CSR_CPUID on 3A5000 is 512, max cpui=
d
> >> 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/in=
clude/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 futur=
e
> >> + * it will be expanded to 4096, including 16 packages at most. And ev=
ery
> >> + * 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/in=
clude/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_inter=
rupt *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, uns=
igned int id, u64 *val)
> >>          return 0;
> >>   }
> >>
> >> +static inline int kvm_set_cpuid(struct kvm_vcpu *vcpu, u64 val)
> >> +{
> >> +       int cpuid;
> >> +       struct loongarch_csrs *csr =3D vcpu->arch.csr;
> >> +       struct kvm_phyid_map  *map;
> >> +
> >> +       if (val >=3D KVM_MAX_PHYID)
> >> +               return -EINVAL;
> >> +
> >> +       cpuid =3D kvm_read_sw_gcsr(csr, LOONGARCH_CSR_ESTAT);
> >> +       map =3D 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 !=3D val) {
> >> +                       /*
> >> +                        * Cpuid 0 is initial value for vcpu, maybe in=
valid
> >> +                        * 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 =3D=3D 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.

Huacai

> >
> >> +
> >> +       if (map->phys_map[val].enabled) {
> >> +               /*
> >> +                * New cpuid is already set with other vcpu
> >> +                * Forbid sharing the same cpuid between different vcp=
us
> >> +                */
> >> +               if (map->phys_map[val].vcpu !=3D 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      =3D true;
> >> +       map->phys_map[val].vcpu         =3D vcpu;
> >> +       if (map->max_phyid < val)
> >> +               map->max_phyid =3D 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 >=3D KVM_MAX_PHYID)
> >> +               return NULL;
> >> +
> >> +       map =3D 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 =3D vcpu->arch.csr;
> >> +       struct kvm_phyid_map  *map;
> >> +
> >> +       map =3D vcpu->kvm->arch.phyid_map;
> >> +       cpuid =3D kvm_read_sw_gcsr(csr, LOONGARCH_CSR_ESTAT);
> >> +       if (cpuid >=3D KVM_MAX_PHYID)
> >> +               return;
> >> +
> >> +       if (map->phys_map[cpuid].enabled) {
> >> +               map->phys_map[cpuid].vcpu =3D NULL;
> >> +               map->phys_map[cpuid].enabled =3D 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 v=
al)
> >>   {
> >>          int ret =3D 0, gintc;
> >> @@ -291,7 +380,8 @@ static int _kvm_setcsr(struct kvm_vcpu *vcpu, unsi=
gned int id, u64 val)
> >>                  kvm_set_sw_gcsr(csr, LOONGARCH_CSR_ESTAT, gintc);
> >>
> >>                  return ret;
> >> -       }
> >> +       } else if (id =3D=3D 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 =3D kvzalloc(sizeof(struct kvm_phyid_map),
> >> +                               GFP_KERNEL_ACCOUNT);
> >> +       if (!kvm->arch.phyid_map) {
> >> +               free_page((unsigned long)kvm->arch.pgd);
> >> +               kvm->arch.pgd =3D NULL;
> >> +               return -ENOMEM;
> >> +       }
> >> +
> >>          kvm_init_vmcs(kvm);
> >>          kvm->arch.gpa_size =3D BIT(cpu_vabits - 1);
> >>          kvm->arch.root_level =3D CONFIG_PGTABLE_LEVELS - 1;
> >> @@ -44,6 +52,7 @@ int kvm_arch_init_vm(struct kvm *kvm, unsigned long =
type)
> >>          for (i =3D 0; i <=3D kvm->arch.root_level; i++)
> >>                  kvm->arch.pte_shifts[i] =3D PAGE_SHIFT + i * (PAGE_SH=
IFT - 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 =3D NULL;
> >> +       kvm->arch.phyid_map =3D NULL;
> >>   }
> >>
> >>   int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
> >> --
> >> 2.39.3
> >>
>