linux-kernel - [PATCH 0/2] KVM: do not assume PTE is writable after follow

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Message-Id: <20210205103259.42866-1-pbonzini@redhat.com>
Date:   Fri,  5 Feb 2021 05:32:57 -0500
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Cc:     jgg@...pe.ca, linux-mm@...ck.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        dan.j.williams@...el.com
Subject: [PATCH 0/2] KVM: do not assume PTE is writable after follow_pfn

This series is the first step towards fixing KVM's usage of follow_pfn.
The immediate fix here is that KVM is not checking the writability of
the PFN, which actually dates back to way before the introduction of
follow_pfn in commit add6a0cd1c5b ("KVM: MMU: try to fix up page faults
before giving up", 2016-07-05).  There are more changes needed to
invalidate gfn-to-pfn caches from MMU notifiers, but this issue will
be tackled later.

A more fundamental issue however is that the follow_pfn function is
basically impossible to use correctly.  Almost all users for example
are assuming that the page is writable; KVM was not alone in this
mistake.  follow_pte, despite not being exported for modules, is a
far saner API.  Therefore, patch 1 simplifies follow_pte a bit and
makes it available to modules.

Please review and possibly ack for inclusion in the KVM tree,
thanks!

Paolo

Paolo Bonzini (2):
  mm: provide a sane PTE walking API for modules
  KVM: do not assume PTE is writable after follow_pfn

 arch/s390/pci/pci_mmio.c |  2 +-
 fs/dax.c                 |  5 +++--
 include/linux/mm.h       |  6 ++++--
 mm/memory.c              | 35 ++++++++++++++++++++++++++++++-----
 virt/kvm/kvm_main.c      | 15 ++++++++++++---
 5 files changed, 50 insertions(+), 13 deletions(-)

-- 
2.26.2