Re: [PATCH v10 15/43] arm64: RME: Allow VMM to set RIPAS

[Gavin Shan <gshan@redhat.com>]

On 8/21/25 12:55 AM, Steven Price wrote:
> Each page within the protected region of the realm guest can be marked
> as either RAM or EMPTY. Allow the VMM to control this before the guest
> has started and provide the equivalent functions to change this (with
> the guest's approval) at runtime.
> 
> When transitioning from RIPAS RAM (1) to RIPAS EMPTY (0) the memory is
> unmapped from the guest and undelegated allowing the memory to be reused
> by the host. When transitioning to RIPAS RAM the actual population of
> the leaf RTTs is done later on stage 2 fault, however it may be
> necessary to allocate additional RTTs to allow the RMM track the RIPAS
> for the requested range.
> 
> When freeing a block mapping it is necessary to temporarily unfold the
> RTT which requires delegating an extra page to the RMM, this page can
> then be recovered once the contents of the block mapping have been
> freed.
> 
> Signed-off-by: Steven Price <steven.price@arm.com>
> ---
> Changes from v9:
>   * Minor coding style fixes.
> Changes from v8:
>   * Propagate the 'may_block' flag to allow conditional calls to
>     cond_resched_rwlock_write().
>   * Introduce alloc_rtt() to wrap alloc_delegated_granule() and
>     kvm_account_pgtable_pages() and use when allocating RTTs.
>   * Code reorganisation to allow init_ipa_state and set_ipa_state to
>     share a common ripas_change() function,
>   * Other minor changes following review.
> Changes from v7:
>   * Replace use of "only_shared" with the upstream "attr_filter" field
>     of struct kvm_gfn_range.
>   * Clean up the logic in alloc_delegated_granule() for when to call
>     kvm_account_pgtable_pages().
>   * Rename realm_destroy_protected_granule() to
>     realm_destroy_private_granule() to match the naming elsewhere. Also
>     fix the return codes in the function to be descriptive.
>   * Several other minor changes to names/return codes.
> Changes from v6:
>   * Split the code dealing with the guest triggering a RIPAS change into
>     a separate patch, so this patch is purely for the VMM setting up the
>     RIPAS before the guest first runs.
>   * Drop the useless flags argument from alloc_delegated_granule().
>   * Account RTTs allocated for a guest using kvm_account_pgtable_pages().
>   * Deal with the RMM granule size potentially being smaller than the
>     host's PAGE_SIZE. Although note alloc_delegated_granule() currently
>     still allocates an entire host page for every RMM granule (so wasting
>     memory when PAGE_SIZE>4k).
> Changes from v5:
>   * Adapt to rebasing.
>   * Introduce find_map_level()
>   * Rename some functions to be clearer.
>   * Drop the "spare page" functionality.
> Changes from v2:
>   * {alloc,free}_delegated_page() moved from previous patch to this one.
>   * alloc_delegated_page() now takes a gfp_t flags parameter.
>   * Fix the reference counting of guestmem pages to avoid leaking memory.
>   * Several misc code improvements and extra comments.
> ---
>   arch/arm64/include/asm/kvm_rme.h |   6 +
>   arch/arm64/kvm/mmu.c             |   8 +-
>   arch/arm64/kvm/rme.c             | 446 +++++++++++++++++++++++++++++++
>   3 files changed, 457 insertions(+), 3 deletions(-)
> 

Reviewed-by: Gavin Shan <gshan@redhat.com>