Re: [RFC PATCH v4 00/14] KVM: Restricted mapping of guest_memfd at the host and arm64 support

Fuad Tabba
2025-01-09T16:35:21Z

Hi,

As mentioned in the guest_memfd sync (2025-01-09), below is the state
diagram that uses the new states in this patch series, and how they
would interact with sharing/unsharing in pKVM:

https://lpc.events/event/18/contributions/1758/attachments/1457/3699/Guestmemfd%20folio%20state%20page_type.pdf

This patch series doesn't necessarily impose all these transitions,
many of them would be a matter of policy. This just happens to be the
current way I've done it with pKVM/arm64.

Cheers,
/fuad

On Fri, 13 Dec 2024 at 16:48, Fuad Tabba <tabba@google.com> wrote:
>
> This series adds restricted mmap() support to guest_memfd, as
> well as support for guest_memfd on arm64. It is based on Linux
> 6.13-rc2. Please refer to v3 for the context [1].
>
> Main changes since v3:
> - Added a new folio type for guestmem, used to register a
> callback when a folio's reference count reaches 0 (Matthew
> Wilcox, DavidH) [2]
> - Introduce new mappability states for folios, where a folio can
> be mappable by the host and the guest, only the guest, or by no
> one (transient state)
> - Rebased on Linux 6.13-rc2
> - Refactoring and tidying up
>
> Cheers,
> /fuad
>
> [1] https://lore.kernel.org/all/20241010085930.1546800-1-tabba@google.com/
> [2] https://lore.kernel.org/all/20241108162040.159038-1-tabba@google.com/
>
> Ackerley Tng (2):
> KVM: guest_memfd: Make guest mem use guest mem inodes instead of
> anonymous inodes
> KVM: guest_memfd: Track mappability within a struct kvm_gmem_private
>
> Fuad Tabba (12):
> mm: Consolidate freeing of typed folios on final folio_put()
> KVM: guest_memfd: Introduce kvm_gmem_get_pfn_locked(), which retains
> the folio lock
> KVM: guest_memfd: Folio mappability states and functions that manage
> their transition
> KVM: guest_memfd: Handle final folio_put() of guestmem pages
> KVM: guest_memfd: Allow host to mmap guest_memfd() pages when shared
> KVM: guest_memfd: Add guest_memfd support to
> kvm_(read|/write)_guest_page()
> KVM: guest_memfd: Add KVM capability to check if guest_memfd is host
> mappable
> KVM: guest_memfd: Add a guest_memfd() flag to initialize it as
> mappable
> KVM: guest_memfd: selftests: guest_memfd mmap() test when mapping is
> allowed
> KVM: arm64: Skip VMA checks for slots without userspace address
> KVM: arm64: Handle guest_memfd()-backed guest page faults
> KVM: arm64: Enable guest_memfd private memory when pKVM is enabled
>
> Documentation/virt/kvm/api.rst | 4 +
> arch/arm64/include/asm/kvm_host.h | 3 +
> arch/arm64/kvm/Kconfig | 1 +
> arch/arm64/kvm/mmu.c | 119 +++-
> include/linux/kvm_host.h | 75 +++
> include/linux/page-flags.h | 22 +
> include/uapi/linux/kvm.h | 2 +
> include/uapi/linux/magic.h | 1 +
> mm/debug.c | 1 +
> mm/swap.c | 28 +-
> tools/testing/selftests/kvm/Makefile | 1 +
> .../testing/selftests/kvm/guest_memfd_test.c | 64 +-
> virt/kvm/Kconfig | 4 +
> virt/kvm/guest_memfd.c | 579 +++++++++++++++++-
> virt/kvm/kvm_main.c | 229 ++++++-
> 15 files changed, 1074 insertions(+), 59 deletions(-)
>
>
> base-commit: fac04efc5c793dccbd07e2d59af9f90b7fc0dca4
> --
> 2.47.1.613.gc27f4b7a9f-goog
>