[PATCH v2 2/4] Revert "KVM: arm64: vgic-its: Don't save collections the table cannot hold"

[Fuad Tabba]

This reverts commit 9b10fb74e4b661543d188701bd4d024fc5c18f58.

Freeing the collections when GITS_BASER<coll> changes removes the state
this check rejected: vgic_its_cmd_handle_mapi(),
vgic_its_cmd_handle_mapc() and vgic_its_restore_cte() all validate the
ID against the current table before allocating, and the table can no
longer change under the list. What remains is a collection whose entry
is not backed by a memslot, which the write fails on anyway, so the
check costs a save userspace should be able to issue reliably and buys
nothing.

The reverted commit credited the check with bounding the walk as well.
It stays bounded without it: collection IDs are unique and each is below
the table's capacity, so the list cannot be longer than the table.

Suggested-by: Marc Zyngier <maz at kernel.org>
Link: https://lore.kernel.org/all/87ecg9owwa.wl-maz@kernel.org/
Signed-off-by: Fuad Tabba <fuad.tabba at linux.dev>
---
 arch/arm64/kvm/vgic/vgic-its.c | 3 ---
 1 file changed, 3 deletions(-)

diff --git a/arch/arm64/kvm/vgic/vgic-its.c b/arch/arm64/kvm/vgic/vgic-its.c
index d5ede640812c4..f702ac31b8b1b 100644
--- a/arch/arm64/kvm/vgic/vgic-its.c
+++ b/arch/arm64/kvm/vgic/vgic-its.c
@@ -2537,9 +2537,6 @@ static int vgic_its_save_collection_table(struct vgic_its *its)
 	max_size = GITS_BASER_NR_PAGES(baser) * SZ_64K;
 
 	list_for_each_entry(collection, &its->collection_list, coll_list) {
-		if (!vgic_its_check_id(its, baser, collection->collection_id, NULL))
-			return -EINVAL;
-
 		ret = vgic_its_save_cte(its, collection, gpa);
 		if (ret)
 			return ret;
-- 
2.39.5