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Date:   Fri, 21 Jul 2023 10:42:58 -0700
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Subject: Re: [RFC PATCH v11 12/29] KVM: Add KVM_CREATE_GUEST_MEMFD ioctl() for
 guest-specific backing memory
From:   Sean Christopherson <seanjc@google.com>
To:     Xiaoyao Li <xiaoyao.li@intel.com>
Cc:     Paolo Bonzini <pbonzini@redhat.com>, Marc Zyngier <maz@kernel.org>,
        Oliver Upton <oliver.upton@linux.dev>,
        Huacai Chen <chenhuacai@kernel.org>,
        Michael Ellerman <mpe@ellerman.id.au>,
        Anup Patel <anup@brainfault.org>,
        Paul Walmsley <paul.walmsley@sifive.com>,
        Palmer Dabbelt <palmer@dabbelt.com>,
        Albert Ou <aou@eecs.berkeley.edu>,
        "Matthew Wilcox (Oracle)" <willy@infradead.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Paul Moore <paul@paul-moore.com>,
        James Morris <jmorris@namei.org>,
        "Serge E. Hallyn" <serge@hallyn.com>, kvm@vger.kernel.org,
        linux-arm-kernel@lists.infradead.org, kvmarm@lists.linux.dev,
        linux-mips@vger.kernel.org, linuxppc-dev@lists.ozlabs.org,
        kvm-riscv@lists.infradead.org, linux-riscv@lists.infradead.org,
        linux-fsdevel@vger.kernel.org, linux-mm@kvack.org,
        linux-security-module@vger.kernel.org,
        linux-kernel@vger.kernel.org,
        Chao Peng <chao.p.peng@linux.intel.com>,
        Fuad Tabba <tabba@google.com>,
        Jarkko Sakkinen <jarkko@kernel.org>,
        Yu Zhang <yu.c.zhang@linux.intel.com>,
        Vishal Annapurve <vannapurve@google.com>,
        Ackerley Tng <ackerleytng@google.com>,
        Maciej Szmigiero <mail@maciej.szmigiero.name>,
        Vlastimil Babka <vbabka@suse.cz>,
        David Hildenbrand <david@redhat.com>,
        Quentin Perret <qperret@google.com>,
        Michael Roth <michael.roth@amd.com>,
        Wang <wei.w.wang@intel.com>,
        Liam Merwick <liam.merwick@oracle.com>,
        Isaku Yamahata <isaku.yamahata@gmail.com>,
        "Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>
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On Fri, Jul 21, 2023, Xiaoyao Li wrote:
> On 7/21/2023 11:05 PM, Xiaoyao Li wrote:
> > On 7/19/2023 7:44 AM, Sean Christopherson wrote:
> > > @@ -6255,12 +6298,17 @@ int kvm_init(unsigned vcpu_size, unsigned
> > > vcpu_align, struct module *module)
> > > =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 if (r)
> > > =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 goto err_async=
_pf;
> > > +=C2=A0=C2=A0=C2=A0 r =3D kvm_gmem_init();
> > > +=C2=A0=C2=A0=C2=A0 if (r)
> > > +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 goto err_gmem;
> > > +
> > > =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 kvm_chardev_ops.owner =3D module;
> > > =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 kvm_preempt_ops.sched_in =3D kvm_sched=
_in;
> > > =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 kvm_preempt_ops.sched_out =3D kvm_sche=
d_out;
> > > =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 kvm_init_debug();
> > > +=C2=A0=C2=A0=C2=A0 kvm_gmem_init();
> >=20
> > why kvm_gmem_init() needs to be called again? by mistake?
>=20
> I'm sure it's a mistake.

Yeah, definitely a bug.

> I'm testing the gmem QEMU with this series. SW_PROTECTED_VM gets stuck in=
 a
> loop in early OVMF code due to two shared page of OVMF get zapped and
> re-mapped infinitely. Removing the second call of kvm_gmem_init() can sol=
ve
> the issue, though I'm not sure about the reason.

Not worth investigating unless you want to satiate your curiosity :-)