linux-kernel - Re: [PATCH 16/21] KVM: arm64: Drop @max param from mmu_topup_memory

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Date:   Thu, 11 Jun 2020 08:59:54 -0700
From:   Sean Christopherson <sean.j.christopherson@...el.com>
To:     Ben Gardon <bgardon@...gle.com>
Cc:     Marc Zyngier <maz@...nel.org>, Paul Mackerras <paulus@...abs.org>,
        Christian Borntraeger <borntraeger@...ibm.com>,
        Janosch Frank <frankja@...ux.ibm.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        James Morse <james.morse@....com>,
        Julien Thierry <julien.thierry.kdev@...il.com>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        David Hildenbrand <david@...hat.com>,
        Cornelia Huck <cohuck@...hat.com>,
        Claudio Imbrenda <imbrenda@...ux.ibm.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>,
        linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.cs.columbia.edu,
        linux-mips@...r.kernel.org, kvm@...r.kernel.org,
        kvm-ppc@...r.kernel.org, linux-kernel@...r.kernel.org,
        Peter Feiner <pfeiner@...gle.com>,
        Peter Shier <pshier@...gle.com>,
        Junaid Shahid <junaids@...gle.com>,
        Christoffer Dall <christoffer.dall@....com>
Subject: Re: [PATCH 16/21] KVM: arm64: Drop @max param from
 mmu_topup_memory_cache()

On Wed, Jun 10, 2020 at 03:00:47PM -0700, Ben Gardon wrote:
> On Fri, Jun 5, 2020 at 2:39 PM Sean Christopherson
> <sean.j.christopherson@...el.com> wrote:
> >
> > Replace the @max param in mmu_topup_memory_cache() and instead use
> > ARRAY_SIZE() to terminate the loop to fill the cache.  This removes a
> > BUG_ON() and sets the stage for moving arm64 to the common memory cache
> > implementation.
> >
> > No functional change intended.
> >
> > Signed-off-by: Sean Christopherson <sean.j.christopherson@...el.com>
> > ---
> >  arch/arm64/kvm/mmu.c | 12 ++++--------
> >  1 file changed, 4 insertions(+), 8 deletions(-)
> >
> > diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
> > index a1f6bc70c4e4..9398b66f8a87 100644
> > --- a/arch/arm64/kvm/mmu.c
> > +++ b/arch/arm64/kvm/mmu.c
> > @@ -124,15 +124,13 @@ static void stage2_dissolve_pud(struct kvm *kvm, phys_addr_t addr, pud_t *pudp)
> >         put_page(virt_to_page(pudp));
> >  }
> >
> > -static int mmu_topup_memory_cache(struct kvm_mmu_memory_cache *cache,
> > -                                 int min, int max)
> > +static int mmu_topup_memory_cache(struct kvm_mmu_memory_cache *cache, int min)
> >  {
> >         void *page;
> >
> > -       BUG_ON(max > KVM_NR_MEM_OBJS);
> KVM_NR_MEM_OBJS should be undefined as of patch 14 in this series. I'd
> recommend changing this to use the new constant you defined in that
> patch.

My intent was to leave KVM_NR_MEM_OBJS defined by arm64 and MIPS until they
move to the common implementation, e.g. this should be defined in
arch/arm64/include/asm/kvm_host.h until patch 18.  I'll get cross-compiling
setup so I can properly test bisection before sending v2.

> >         if (cache->nobjs >= min)
> >                 return 0;
> > -       while (cache->nobjs < max) {
> > +       while (cache->nobjs < ARRAY_SIZE(cache->objects)) {
> >                 page = (void *)__get_free_page(GFP_PGTABLE_USER);
> >                 if (!page)
> >                         return -ENOMEM;
> > @@ -1356,8 +1354,7 @@ int kvm_phys_addr_ioremap(struct kvm *kvm, phys_addr_t guest_ipa,
> >                         pte = kvm_s2pte_mkwrite(pte);
> >
> >                 ret = mmu_topup_memory_cache(&cache,
> > -                                            kvm_mmu_cache_min_pages(kvm),
> > -                                            KVM_NR_MEM_OBJS);
> See above, KVM_NR_MEM_OBJS is undefined as of patch 14.
> > +                                            kvm_mmu_cache_min_pages(kvm));
> >                 if (ret)
> >                         goto out;
> >                 spin_lock(&kvm->mmu_lock);
> > @@ -1737,8 +1734,7 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
> >         up_read(&current->mm->mmap_sem);
> >
> >         /* We need minimum second+third level pages */
> > -       ret = mmu_topup_memory_cache(memcache, kvm_mmu_cache_min_pages(kvm),
> > -                                    KVM_NR_MEM_OBJS);
> See above, KVM_NR_MEM_OBJS is undefined as of patch 14.
> > +       ret = mmu_topup_memory_cache(memcache, kvm_mmu_cache_min_pages(kvm));
> >         if (ret)
> >                 return ret;
> >
> > --
> > 2.26.0
> >