[v4,0/4] KVM: allow mapping non-refcounted pages

Message

David Stevens Sept. 29, 2021, 4:29 a.m. UTC

From: David Stevens <[e-mail]>

This patch series adds support for mapping non-refcount VM_IO and
VM_PFNMAP memory into the guest.

Currently, the gfn_to_pfn functions require being able to pin the target
pfn, so they will fail if the pfn returned by follow_pte isn't a
ref-counted page.  However, the KVM secondary MMUs do not require that
the pfn be pinned, since they are integrated with the mmu notifier API.
This series adds a new set of gfn_to_pfn_page functions which parallel
the gfn_to_pfn functions but do not pin the pfn. The new functions
return the page from gup if it was present, so callers can use it and
call put_page when done.

The gfn_to_pfn functions should be depreciated, since as they are unsafe
due to relying on trying to obtain a struct page from a pfn returned by
follow_pte. I added new functions instead of simply adding another
optional parameter to the existing functions to make it easier to track
down users of the deprecated functions.

This series updates x86 and arm64 secondary MMUs to the new API.

v3 -> v4:
 - rebase on kvm next branch again
 - Add some more context to a comment in ensure_pfn_ref
v2 -> v3:
 - rebase on kvm next branch
v1 -> v2:
 - Introduce new gfn_to_pfn_page functions instead of modifying the
   behavior of existing gfn_to_pfn functions, to make the change less
   invasive.
 - Drop changes to mmu_audit.c
 - Include Nicholas Piggin's patch to avoid corrupting refcount in the
   follow_pte case, and use it in depreciated gfn_to_pfn functions.
 - Rebase on kvm/next

David Stevens (4):
  KVM: mmu: introduce new gfn_to_pfn_page functions
  KVM: x86/mmu: use gfn_to_pfn_page
  KVM: arm64/mmu: use gfn_to_pfn_page
  KVM: mmu: remove over-aggressive warnings

 arch/arm64/kvm/mmu.c            |  27 +++--
 arch/x86/kvm/mmu/mmu.c          |  50 ++++----
 arch/x86/kvm/mmu/mmu_internal.h |   3 +-
 arch/x86/kvm/mmu/paging_tmpl.h  |  23 ++--
 arch/x86/kvm/mmu/tdp_mmu.c      |   6 +-
 arch/x86/kvm/mmu/tdp_mmu.h      |   4 +-
 arch/x86/kvm/x86.c              |   6 +-
 include/linux/kvm_host.h        |  17 +++
 virt/kvm/kvm_main.c             | 198 +++++++++++++++++++++++---------
 9 files changed, 231 insertions(+), 103 deletions(-)