ANDROID: ARM64: virtio_balloon: Disable balloon with warning if granule too large

If the reporting granule is larger than guest page size, we cannot
safely relinquish memory to the hypervisor.

Bug: 381400679
Bug: 357781595
Change-Id: I84461c21e44209021afe617ed2796108c5c43718
Signed-off-by: Keir Fraser <keirf@google.com>

drivers/virt/coco/pkvm-guest/arm-pkvm-guest.c

@@ -114,6 +114,12 @@ static int mmio_guard_ioremap_hook(phys_addr_t phys, size_t size,
 
 static bool mem_relinquish_available;
 
+bool page_relinquish_disallowed(void)
+{
+	return mem_relinquish_available && (pkvm_granule > PAGE_SIZE);
+}
+EXPORT_SYMBOL_GPL(page_relinquish_disallowed);
+
 void page_relinquish(struct page *page)
 {
 	phys_addr_t phys, end;

drivers/virtio/virtio_balloon.c

@@ -1182,6 +1182,9 @@ static int virtballoon_restore(struct virtio_device *vdev)
 
 static int virtballoon_validate(struct virtio_device *vdev)
 {
+	if (WARN_ON(page_relinquish_disallowed()))
+		return -EINVAL;
+
 	/*
 	 * Inform the hypervisor that our pages are poisoned or
 	 * initialized. If we cannot do that then we should disable

include/linux/mem_relinquish.h

@@ -11,10 +11,12 @@ struct page;
 
 #ifdef CONFIG_MEMORY_RELINQUISH
 
+bool page_relinquish_disallowed(void);
 void page_relinquish(struct page *page);
 
 #else	/* !CONFIG_MEMORY_RELINQUISH */
 
+static inline bool page_relinquish_disallowed(void) { return false; }
 static inline void page_relinquish(struct page *page) { }
 
 #endif	/* CONFIG_MEMORY_RELINQUISH */