linux-kernel - Re: [PATCH v3 2/8] KVM: x86/mmu: Factor out allocating memslot rmap

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Date:   Mon, 10 May 2021 09:29:14 -0700
From:   Ben Gardon <bgardon@...gle.com>
To:     David Hildenbrand <david@...hat.com>
Cc:     LKML <linux-kernel@...r.kernel.org>, kvm <kvm@...r.kernel.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Peter Xu <peterx@...hat.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Peter Shier <pshier@...gle.com>,
        Yulei Zhang <yulei.kernel@...il.com>,
        Wanpeng Li <kernellwp@...il.com>,
        Xiao Guangrong <xiaoguangrong.eric@...il.com>,
        Kai Huang <kai.huang@...el.com>,
        Keqian Zhu <zhukeqian1@...wei.com>
Subject: Re: [PATCH v3 2/8] KVM: x86/mmu: Factor out allocating memslot rmap

On Fri, May 7, 2021 at 12:47 AM David Hildenbrand <david@...hat.com> wrote:
>
> On 06.05.21 20:42, Ben Gardon wrote:
> > Small refactor to facilitate allocating rmaps for all memslots at once.
> >
> > No functional change expected.
> >
> > Signed-off-by: Ben Gardon <bgardon@...gle.com>
> > ---
> >   arch/x86/kvm/x86.c | 41 ++++++++++++++++++++++++++++++++---------
> >   1 file changed, 32 insertions(+), 9 deletions(-)
> >
> > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> > index 5bcf07465c47..fc32a7dbe4c4 100644
> > --- a/arch/x86/kvm/x86.c
> > +++ b/arch/x86/kvm/x86.c
> > @@ -10842,10 +10842,37 @@ void kvm_arch_free_memslot(struct kvm *kvm, struct kvm_memory_slot *slot)
> >       kvm_page_track_free_memslot(slot);
> >   }
> >
> > +static int alloc_memslot_rmap(struct kvm_memory_slot *slot,
> > +                           unsigned long npages)
>
> I'd have called the functions memslot_rmap_alloc() and memslot_rmap_free()
>
>
> > +{
> > +     int i;
> > +
> > +     for (i = 0; i < KVM_NR_PAGE_SIZES; ++i) {
> > +             int lpages;
> > +             int level = i + 1;
> > +
> > +             lpages = gfn_to_index(slot->base_gfn + npages - 1,
> > +                                   slot->base_gfn, level) + 1;
> > +
> > +             slot->arch.rmap[i] =
> > +                     kvcalloc(lpages, sizeof(*slot->arch.rmap[i]),
> > +                              GFP_KERNEL_ACCOUNT);
> > +             if (!slot->arch.rmap[i])
> > +                     goto out_free;
>
> you can just avoid the goto here and do the free_memslot_rmap() right away.

Oh good catch. I'll incorporate your suggestions in v4.

>
> > +     }
> > +
> > +     return 0;
> > +
> > +out_free:
> > +     free_memslot_rmap(slot);
> > +     return -ENOMEM;
> > +}
> > +
> >   static int kvm_alloc_memslot_metadata(struct kvm_memory_slot *slot,
> >                                     unsigned long npages)
> >   {
> >       int i;
> > +     int r;
> >
> >       /*
> >        * Clear out the previous array pointers for the KVM_MR_MOVE case.  The
> > @@ -10854,7 +10881,11 @@ static int kvm_alloc_memslot_metadata(struct kvm_memory_slot *slot,
> >        */
> >       memset(&slot->arch, 0, sizeof(slot->arch));
> >
> > -     for (i = 0; i < KVM_NR_PAGE_SIZES; ++i) {
> > +     r = alloc_memslot_rmap(slot, npages);
> > +     if (r)
> > +             return r;
> > +
> > +     for (i = 1; i < KVM_NR_PAGE_SIZES; ++i) {
> >               struct kvm_lpage_info *linfo;
> >               unsigned long ugfn;
> >               int lpages;
> > @@ -10863,14 +10894,6 @@ static int kvm_alloc_memslot_metadata(struct kvm_memory_slot *slot,
> >               lpages = gfn_to_index(slot->base_gfn + npages - 1,
> >                                     slot->base_gfn, level) + 1;
> >
> > -             slot->arch.rmap[i] =
> > -                     kvcalloc(lpages, sizeof(*slot->arch.rmap[i]),
> > -                              GFP_KERNEL_ACCOUNT);
> > -             if (!slot->arch.rmap[i])
> > -                     goto out_free;
> > -             if (i == 0)
> > -                     continue;
> > -
> >               linfo = kvcalloc(lpages, sizeof(*linfo), GFP_KERNEL_ACCOUNT);
> >               if (!linfo)
> >                       goto out_free;
> >
>
> apart from that LGTM
>
> --
> Thanks,
>
> David / dhildenb
>