linux-kernel - Re: [RFC PATCH v11 13/29] KVM: Add transparent hugepage support for dedicated guest memory

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Date:   Thu, 7 Sep 2023 00:10:13 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Sean Christopherson <seanjc@...gle.com>
Cc:     Marc Zyngier <maz@...nel.org>,
        Oliver Upton <oliver.upton@...ux.dev>,
        Huacai Chen <chenhuacai@...nel.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        Anup Patel <anup@...infault.org>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        "Matthew Wilcox (Oracle)" <willy@...radead.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Paul Moore <paul@...l-moore.com>,
        James Morris <jmorris@...ei.org>,
        "Serge E. Hallyn" <serge@...lyn.com>, kvm@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.linux.dev,
        linux-mips@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        kvm-riscv@...ts.infradead.org, linux-riscv@...ts.infradead.org,
        linux-fsdevel@...r.kernel.org, linux-mm@...ck.org,
        linux-security-module@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Chao Peng <chao.p.peng@...ux.intel.com>,
        Fuad Tabba <tabba@...gle.com>,
        Jarkko Sakkinen <jarkko@...nel.org>,
        Yu Zhang <yu.c.zhang@...ux.intel.com>,
        Vishal Annapurve <vannapurve@...gle.com>,
        Ackerley Tng <ackerleytng@...gle.com>,
        Maciej Szmigiero <mail@...iej.szmigiero.name>,
        Vlastimil Babka <vbabka@...e.cz>,
        David Hildenbrand <david@...hat.com>,
        Quentin Perret <qperret@...gle.com>,
        Michael Roth <michael.roth@....com>,
        Wang <wei.w.wang@...el.com>,
        Liam Merwick <liam.merwick@...cle.com>,
        Isaku Yamahata <isaku.yamahata@...il.com>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>
Subject: Re: [RFC PATCH v11 13/29] KVM: Add transparent hugepage support for
 dedicated guest memory

On Fri, Jul 21, 2023 at 7:13 PM Sean Christopherson <seanjc@...gle.com> wrote:
> On Fri, Jul 21, 2023, Paolo Bonzini wrote:
> > On 7/19/23 01:44, Sean Christopherson wrote:
> > > @@ -413,6 +454,9 @@ int kvm_gmem_create(struct kvm *kvm, struct kvm_create_guest_memfd *args)
> > >     u64 flags = args->flags;
> > >     u64 valid_flags = 0;
> > > +   if (IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE))
> > > +           valid_flags |= KVM_GUEST_MEMFD_ALLOW_HUGEPAGE;
> > > +
> >
> > I think it should be always allowed.  The outcome would just be "never have
> > a hugepage" if thp is not enabled in the kernel.
>
> I don't have a strong preference.  My thinking was that userspace would probably
> rather have an explicit error, as opposed to silently running with a misconfigured
> setup.

Considering that is how madvise(MADV_HUGEPAGE) behaves, your patch is
good. I disagree but consistency is better.

Paolo