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Message-ID: <4cdd93ba-9019-4c12-a0e6-07b430980278@redhat.com>
Date: Tue, 6 Aug 2024 15:51:22 +0200
From: David Hildenbrand <david@...hat.com>
To: Elliot Berman <quic_eberman@...cinc.com>,
Andrew Morton <akpm@...ux-foundation.org>,
Paolo Bonzini <pbonzini@...hat.com>, Sean Christopherson
<seanjc@...gle.com>, Fuad Tabba <tabba@...gle.com>,
Patrick Roy <roypat@...zon.co.uk>, qperret@...gle.com,
Ackerley Tng <ackerleytng@...gle.com>
Cc: linux-coco@...ts.linux.dev, linux-arm-msm@...r.kernel.org,
linux-kernel@...r.kernel.org, linux-mm@...ck.org, kvm@...r.kernel.org
Subject: Re: [PATCH RFC 4/4] mm: guest_memfd: Add ability for mmap'ing pages
>
> - if (gmem_flags & GUEST_MEMFD_FLAG_NO_DIRECT_MAP) {
> + if (!ops->accessible && (gmem_flags & GUEST_MEMFD_FLAG_NO_DIRECT_MAP)) {
> r = guest_memfd_folio_private(folio);
> if (r)
> goto out_err;
> @@ -107,6 +109,82 @@ struct folio *guest_memfd_grab_folio(struct file *file, pgoff_t index, u32 flags
> }
> EXPORT_SYMBOL_GPL(guest_memfd_grab_folio);
>
> +int guest_memfd_make_inaccessible(struct file *file, struct folio *folio)
> +{
> + unsigned long gmem_flags = (unsigned long)file->private_data;
> + unsigned long i;
> + int r;
> +
> + unmap_mapping_folio(folio);
> +
> + /**
> + * We can't use the refcount. It might be elevated due to
> + * guest/vcpu trying to access same folio as another vcpu
> + * or because userspace is trying to access folio for same reason
As discussed, that's insufficient. We really have to drive the refcount
to 1 -- the single reference we expect.
What is the exact problem you are running into here? Who can just grab a
reference and maybe do nasty things with it?
--
Cheers,
David / dhildenb
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