[PATCH v2 1/3] KVM: arm64: Reset page order in pKVM hyp_pool_init

[Vincent Donnefort]

When a VM fails to initialise after its stage-2 hyp_pool has been
initialised, that stage-2 must be torn down entirely. This requires
resetting both the refcount and the order of its pages back to 0.

Currently, reclaim_pgtable_pages() implicitly resets the page order by
allocating the entire pool with order-0 granularity. However, in the VM
initialisation error path, the addresses of the donated memory (the PGD)
are already known, making it unnecessary to iterate over all pages in
the pool.

Since the vmemmap page order is a hyp_pool-specific field, leaving a
non-zero order on hyp_pool destruction is harmless until another pool
attempts to admit the page. Instead of resetting this field during
destruction, reset it during pool initialization in hyp_pool_init().
Note that pages added to the pool outside of the initial pool range
(e.g., via guest_s2_zalloc_page()) must still have their order managed
manually.

While at it, add a WARN_ON() in the hyp_pool attach path to catch
unexpected page orders that exceed the pool's max_order.

Fixes: 256b4668cd89 ("KVM: arm64: Introduce separate hypercalls for pKVM VM reservation and initialization")
Reported-by: Sashiko <sashiko-bot at kernel.org>
Signed-off-by: Vincent Donnefort <vdonnefort at google.com>

diff --git a/arch/arm64/kvm/hyp/nvhe/mem_protect.c b/arch/arm64/kvm/hyp/nvhe/mem_protect.c
index 25f04629014e..89eb20d4fee4 100644
--- a/arch/arm64/kvm/hyp/nvhe/mem_protect.c
+++ b/arch/arm64/kvm/hyp/nvhe/mem_protect.c
@@ -322,7 +322,6 @@ void reclaim_pgtable_pages(struct pkvm_hyp_vm *vm, struct kvm_hyp_memcache *mc)
 	while (addr) {
 		page = hyp_virt_to_page(addr);
 		page->refcount = 0;
-		page->order = 0;
 		push_hyp_memcache(mc, addr, hyp_virt_to_phys);
 		WARN_ON(__pkvm_hyp_donate_host(hyp_virt_to_pfn(addr), 1));
 		addr = hyp_alloc_pages(&vm->pool, 0);
diff --git a/arch/arm64/kvm/hyp/nvhe/page_alloc.c b/arch/arm64/kvm/hyp/nvhe/page_alloc.c
index a1eb27a1a747..c3b3dc5a8ea7 100644
--- a/arch/arm64/kvm/hyp/nvhe/page_alloc.c
+++ b/arch/arm64/kvm/hyp/nvhe/page_alloc.c
@@ -97,6 +97,8 @@ static void __hyp_attach_page(struct hyp_pool *pool,
 	u8 order = p->order;
 	struct hyp_page *buddy;
 
+	WARN_ON(p->order > pool->max_order);
+
 	memset(hyp_page_to_virt(p), 0, PAGE_SIZE << p->order);
 
 	/* Skip coalescing for 'external' pages being freed into the pool. */
@@ -237,8 +239,10 @@ int hyp_pool_init(struct hyp_pool *pool, u64 pfn, unsigned int nr_pages,
 
 	/* Init the vmemmap portion */
 	p = hyp_phys_to_page(phys);
-	for (i = 0; i < nr_pages; i++)
+	for (i = 0; i < nr_pages; i++) {
 		hyp_set_page_refcounted(&p[i]);
+		p[i].order = 0;
+	}
 
 	/* Attach the unused pages to the buddy tree */
 	for (i = reserved_pages; i < nr_pages; i++)
-- 
2.54.0.746.g67dd491aae-goog