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From:   Vishal Annapurve <vannapurve@google.com>
Date:   Wed, 19 Jul 2023 10:21:55 -0700
Message-ID: <CAGtprH9a2jX-hdww9GPuMrO9noNeXkoqE8oejtVn2vD0AZa3zA@mail.gmail.com>
Subject: Re: [RFC PATCH v11 12/29] KVM: Add KVM_CREATE_GUEST_MEMFD ioctl() for
 guest-specific backing memory
To:     Sean Christopherson <seanjc@google.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,
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        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>,
        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 Tue, Jul 18, 2023 at 4:49=E2=80=AFPM Sean Christopherson <seanjc@google.=
com> wrote:
> ...
> +static int kvm_gmem_error_page(struct address_space *mapping, struct pag=
e *page)
> +{
> +       struct list_head *gmem_list =3D &mapping->private_list;
> +       struct kvm_memory_slot *slot;
> +       struct kvm_gmem *gmem;
> +       unsigned long index;
> +       pgoff_t start, end;
> +       gfn_t gfn;
> +
> +       filemap_invalidate_lock_shared(mapping);
> +
> +       start =3D page->index;
> +       end =3D start + thp_nr_pages(page);
> +
> +       list_for_each_entry(gmem, gmem_list, entry) {
> +               xa_for_each_range(&gmem->bindings, index, slot, start, en=
d - 1) {
> +                       for (gfn =3D start; gfn < end; gfn++) {
> +                               if (WARN_ON_ONCE(gfn < slot->base_gfn ||
> +                                               gfn >=3D slot->base_gfn +=
 slot->npages))
> +                                       continue;
> +
> +                               /*
> +                                * FIXME: Tell userspace that the *privat=
e*
> +                                * memory encountered an error.
> +                                */
> +                               send_sig_mceerr(BUS_MCEERR_AR,
> +                                               (void __user *)gfn_to_hva=
_memslot(slot, gfn),
> +                                               PAGE_SHIFT, current);

Does it make sense to replicate what happens with MCE handling on
tmpfs backed guest memory:
1) Unmap gpa from guest
2) On the next guest EPT fault, exit to userspace to handle/log the
mce error for the gpa.

IIUC, such MCEs could be asynchronous and "current" might not always
be the intended recipient of this signal.

> +                       }
> +               }
> +       }
> +
> +       filemap_invalidate_unlock_shared(mapping);
> +
> +       return 0;
> +}
> +