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From:   Paolo Bonzini <pbonzini@redhat.com>
Date:   Sun, 5 Nov 2023 17:19:36 +0100
Message-ID: <CABgObfb1Wf2ptitGhJPM6VcmkCG9haMoQj2BsttjeoV=9F0O9Q@mail.gmail.com>
Subject: Re: [PATCH v13 20/35] KVM: x86/mmu: Handle page fault for private memory
To:     Xu Yilun <yilun.xu@linux.intel.com>
Cc:     Sean Christopherson <seanjc@google.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>,
        Alexander Viro <viro@zeniv.linux.org.uk>,
        Christian Brauner <brauner@kernel.org>,
        "Matthew Wilcox (Oracle)" <willy@infradead.org>,
        Andrew Morton <akpm@linux-foundation.org>, kvm@vger.kernel.org,
        linux-arm-kernel@lists.infradead.org, kvmarm@lists.linux.dev,
        linux-mips@vger.kernel.org, linuxppc-dev@lists.ozlabs.org,
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        linux-kernel@vger.kernel.org, Xiaoyao Li <xiaoyao.li@intel.com>,
        Xu Yilun <yilun.xu@intel.com>,
        Chao Peng <chao.p.peng@linux.intel.com>,
        Fuad Tabba <tabba@google.com>,
        Jarkko Sakkinen <jarkko@kernel.org>,
        Anish Moorthy <amoorthy@google.com>,
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        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 Sun, Nov 5, 2023 at 2:04=E2=80=AFPM Xu Yilun <yilun.xu@linux.intel.com> =
wrote:
>
> > +static void kvm_mmu_prepare_memory_fault_exit(struct kvm_vcpu *vcpu,
> > +                                           struct kvm_page_fault *faul=
t)
> > +{
> > +     kvm_prepare_memory_fault_exit(vcpu, fault->gfn << PAGE_SHIFT,
> > +                                   PAGE_SIZE, fault->write, fault->exe=
c,
> > +                                   fault->is_private);
> > +}
> > +
> > +static int kvm_faultin_pfn_private(struct kvm_vcpu *vcpu,
> > +                                struct kvm_page_fault *fault)
> > +{
> > +     int max_order, r;
> > +
> > +     if (!kvm_slot_can_be_private(fault->slot)) {
> > +             kvm_mmu_prepare_memory_fault_exit(vcpu, fault);
> > +             return -EFAULT;
> > +     }
> > +
> > +     r =3D kvm_gmem_get_pfn(vcpu->kvm, fault->slot, fault->gfn, &fault=
->pfn,
> > +                          &max_order);
> > +     if (r) {
> > +             kvm_mmu_prepare_memory_fault_exit(vcpu, fault);
> > +             return r;
>
> Why report KVM_EXIT_MEMORY_FAULT here? even with a ret !=3D -EFAULT?

The cases are EFAULT, EHWPOISON (which can report
KVM_EXIT_MEMORY_FAULT) and ENOMEM. I think it's fine
that even -ENOMEM can return KVM_EXIT_MEMORY_FAULT,
and it doesn't violate the documentation.  The docs tell you "what
can you do if error if EFAULT or EHWPOISON?"; they don't
exclude that other errnos result in KVM_EXIT_MEMORY_FAULT,
it's just that you're not supposed to look at it

Paolo