linux-kernel - Re: [Patch v3 6/9] KVM: Provide NUMA node support to kvm_mmu_memory

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Date:   Tue, 3 Jan 2023 09:36:51 -0800
From:   Vipin Sharma <vipinsh@...gle.com>
To:     chenhuacai@...nel.org, aleksandar.qemu.devel@...il.com
Cc:     seanjc@...gle.com, pbonzini@...hat.com, dmatlack@...gle.com,
        kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        Ben Gardon <bgardon@...gle.com>
Subject: Re: [Patch v3 6/9] KVM: Provide NUMA node support to kvm_mmu_memory_cache{}

On Thu, Dec 29, 2022 at 10:22 AM Ben Gardon <bgardon@...gle.com> wrote:
>
> On Wed, Dec 28, 2022 at 2:08 PM Vipin Sharma <vipinsh@...gle.com> wrote:
> >
> > On Tue, Dec 27, 2022 at 11:10 AM Ben Gardon <bgardon@...gle.com> wrote:
> > >
> > > On Wed, Dec 21, 2022 at 6:35 PM Vipin Sharma <vipinsh@...gle.com> wrote:
> > > >
> > > > Add 'node' variable in kvm_mmu_memory_cache{} to denote which NUMA node
> > > > this cache should allocate memory from. Default initialize to
> > > > NUMA_NO_NODE in all architectures.
> > > >
> > > > Signed-off-by: Vipin Sharma <vipinsh@...gle.com>
> > > > ---
> > > >  arch/arm64/kvm/arm.c      |  2 +-
> > > >  arch/arm64/kvm/mmu.c      |  4 +++-
> > > >  arch/mips/kvm/mips.c      |  2 ++
> > > >  arch/riscv/kvm/mmu.c      |  2 +-
> > > >  arch/riscv/kvm/vcpu.c     |  2 +-
> > > >  arch/x86/kvm/mmu/mmu.c    | 22 ++++++++++++----------
> > > >  include/linux/kvm_host.h  |  6 ++++++
> > > >  include/linux/kvm_types.h |  2 ++
> > > >  8 files changed, 28 insertions(+), 14 deletions(-)
> > > >
> > > > diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c
> > > > index 9c5573bc4614..52a41f4532e2 100644
> > > > --- a/arch/arm64/kvm/arm.c
> > > > +++ b/arch/arm64/kvm/arm.c
> > > > @@ -340,7 +340,7 @@ int kvm_arch_vcpu_create(struct kvm_vcpu *vcpu)
> > > >         vcpu->arch.target = -1;
> > > >         bitmap_zero(vcpu->arch.features, KVM_VCPU_MAX_FEATURES);
> > > >
> > > > -       vcpu->arch.mmu_page_cache.gfp_zero = __GFP_ZERO;
> > > > +       INIT_KVM_MMU_MEMORY_CACHE(&vcpu->arch.mmu_page_cache, NULL, NUMA_NO_NODE);
> > > >
> > > >         /*
> > > >          * Default value for the FP state, will be overloaded at load
> > > > diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
> > > > index 31d7fa4c7c14..bd07155e17fa 100644
> > > > --- a/arch/arm64/kvm/mmu.c
> > > > +++ b/arch/arm64/kvm/mmu.c
> > > > @@ -894,12 +894,14 @@ int kvm_phys_addr_ioremap(struct kvm *kvm, phys_addr_t guest_ipa,
> > > >  {
> > > >         phys_addr_t addr;
> > > >         int ret = 0;
> > > > -       struct kvm_mmu_memory_cache cache = { .gfp_zero = __GFP_ZERO };
> > > > +       struct kvm_mmu_memory_cache cache;
> > > >         struct kvm_pgtable *pgt = kvm->arch.mmu.pgt;
> > > >         enum kvm_pgtable_prot prot = KVM_PGTABLE_PROT_DEVICE |
> > > >                                      KVM_PGTABLE_PROT_R |
> > > >                                      (writable ? KVM_PGTABLE_PROT_W : 0);
> > > >
> > > > +       INIT_KVM_MMU_MEMORY_CACHE(&cache, NULL, NUMA_NO_NODE);
> > > > +
> > > >         if (is_protected_kvm_enabled())
> > > >                 return -EPERM;
> > > >
> > > > diff --git a/arch/mips/kvm/mips.c b/arch/mips/kvm/mips.c
> > > > index a25e0b73ee70..b017c29a9340 100644
> > > > --- a/arch/mips/kvm/mips.c
> > > > +++ b/arch/mips/kvm/mips.c
> > > > @@ -304,6 +304,8 @@ int kvm_arch_vcpu_create(struct kvm_vcpu *vcpu)
> > > >                      HRTIMER_MODE_REL);
> > > >         vcpu->arch.comparecount_timer.function = kvm_mips_comparecount_wakeup;
> > > >
> > > > +       vcpu->arch.mmu_page_cache.node = NUMA_NO_NODE;
> > > > +
> > >
> > > It looks weird to have MIPS not using the initialization MACRO. Should
> > > it just have a GFP_ZERO parameter?
> >
> > MIPS is not setting GFP_ZERO explicitly before my series, so, I didn't
> > make it GFP_ZERO. I am not sure if MIPS needs it or not, I tried to
> > keep the same functionality in my patch.
> >
> > May be someone from MIPS can tell more about it.
>
> That makes sense, I just don't want to see MIPS get left behind
> because we move the cache init logic to a macro or function. Folks
> might update the init function but forget to update MIPS too.
>

Hi Huacai, Aleksandar,

I have noticed that MIPS doesn't use __GFP_ZERO flag for
mmu_page_cache in KVM. Is it intentional? I was wondering if it will
be useful if I add zero flag for cache in this patch for MIPS? All
other architectures seem to use __GFP_ZERO flag for their caches.

Thanks
Vipin