KVM: arm64: Reset page order in pKVM hyp_pool

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().

For 'external' pages, we can't trust the order either as they bypass
hyp_pool_init(). Since we never coalesce them, enforce order-0 to ensure
safe insertion into the pool.

This leaves no vmemmap order users outside of hyp_pool.

Fixes: 256b4668cd89 ("KVM: arm64: Introduce separate hypercalls for pKVM VM reservation and initialization")
Reported-by: Sashiko <sashiko-bot@kernel.org>
Signed-off-by: Vincent Donnefort <vdonnefort@google.com>
Reviewed-by: Fuad Tabba <tabba@google.com>
Tested-by: Fuad Tabba <tabba@google.com>
Link: https://patch.msgid.link/20260521143626.1005660-2-vdonnefort@google.com
Signed-off-by: Marc Zyngier <maz@kernel.org>

diff --git a/arch/arm64/kvm/hyp/nvhe/mem_protect.c b/arch/arm64/kvm/hyp/nvhe/mem_protect.c
index 28a471d1927cd50f908ea0dc14b8f583700d1cd8..5c1e1742db4f0d81c7ee9f8259fbcf285b4e4cae 100644 (file)
--- a/arch/arm64/kvm/hyp/nvhe/mem_protect.c
+++ b/arch/arm64/kvm/hyp/nvhe/mem_protect.c
@@ -202,7 +202,6 @@ static void *guest_s2_zalloc_page(void *mc)
        memset(addr, 0, PAGE_SIZE);
        p = hyp_virt_to_page(addr);
        p->refcount = 1;
-       p->order = 0;
 
        return addr;
 }
@@ -307,7 +306,6 @@ 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 a1eb27a1a74774a63e653ad6219edac28c1ea249..57f86aa0f82fcb830afa4be0cf9d2fd35014e990 100644 (file)
--- a/arch/arm64/kvm/hyp/nvhe/page_alloc.c
+++ b/arch/arm64/kvm/hyp/nvhe/page_alloc.c
@@ -94,13 +94,22 @@ static void __hyp_attach_page(struct hyp_pool *pool,
                              struct hyp_page *p)
 {
        phys_addr_t phys = hyp_page_to_phys(p);
-       u8 order = p->order;
        struct hyp_page *buddy;
+       bool coalesce = true;
+       u8 order = p->order;
 
-       memset(hyp_page_to_virt(p), 0, PAGE_SIZE << p->order);
+       /*
+        * 'external' pages are never coalesced and their ->order field
+        * untrusted as they bypass hyp_pool_init(). Enforce order-0.
+        */
+       if (phys < pool->range_start || phys >= pool->range_end) {
+               order = 0;
+               coalesce = false;
+       }
+
+       memset(hyp_page_to_virt(p), 0, PAGE_SIZE << order);
 
-       /* Skip coalescing for 'external' pages being freed into the pool. */
-       if (phys < pool->range_start || phys >= pool->range_end)
+       if (!coalesce)
                goto insert;
 
        /*
@@ -237,8 +246,10 @@ 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++)