mm: kfence: pass a pointer to virt_to_page()

Functions that work on a pointer to virtual memory such as virt_to_pfn()
and users of that function such as virt_to_page() are supposed to pass a
pointer to virtual memory, ideally a (void *) or other pointer.  However
since many architectures implement virt_to_pfn() as a macro, this function
becomes polymorphic and accepts both a (unsigned long) and a (void *).

If we instead implement a proper virt_to_pfn(void *addr) function the
following happens (occurred on arch/arm):

mm/kfence/core.c:558:30: warning: passing argument 1
  of 'virt_to_pfn' makes pointer from integer without a
  cast [-Wint-conversion]

In one case we can refer to __kfence_pool directly (and that is a proper
(char *) pointer) and in the other call site we use an explicit cast.

Link: https://lkml.kernel.org/r/20220630084124.691207-4-linus.walleij@linaro.orgSigned-off-by: Linus Walleij <linus.walleij@linaro.org>
Reviewed-by: Marco Elver <elver@google.com>
Cc: Alexander Potapenko <glider@google.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Jason Gunthorpe <jgg@nvidia.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm/kfence/core.c

@@ -546,7 +546,7 @@ static unsigned long kfence_init_pool(void)
 	if (!arch_kfence_init_pool())
 		return addr;
 
-	pages = virt_to_page(addr);
+	pages = virt_to_page(__kfence_pool);
 
 	/*
 	 * Set up object pages: they must have PG_slab set, to avoid freeing
@@ -660,7 +660,7 @@ static bool kfence_init_pool_late(void)
 	/* Same as above. */
 	free_size = KFENCE_POOL_SIZE - (addr - (unsigned long)__kfence_pool);
 #ifdef CONFIG_CONTIG_ALLOC
-	free_contig_range(page_to_pfn(virt_to_page(addr)), free_size / PAGE_SIZE);
+	free_contig_range(page_to_pfn(virt_to_page((void *)addr)), free_size / PAGE_SIZE);
 #else
 	free_pages_exact((void *)addr, free_size);
 #endif