arm64: vdso: remove aarch32_vdso_pages[]

The aarch32_vdso_pages[] array is unnecessarily confusing. We only ever
use the C_VECTORS and C_SIGPAGE slots, and the other slots are unused
despite having corresponding mappings (sharing pages with the AArch64
vDSO).

Let's make this clearer by using separate variables for the vectors page
and the sigreturn page. A subsequent patch will clean up the C_* naming
and conflation of pages with mappings.

Note that since both the vectors page and sig page are single
pages, and the mapping is a single page long, their pages array do not
need to be NULL-terminated (and this was not the case with the existing
code for the sig page as it was the last entry in the aarch32_vdso_pages
array).

There should be no functional change as a result of this patch.

Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Vincenzo Frascino <vincenzo.frascino@arm.com>
Cc: Will Deacon <will@kernel.org>
Link: https://lore.kernel.org/r/20200428164921.41641-2-mark.rutland@arm.com
Signed-off-by: Will Deacon <will@kernel.org>

arch/arm64/kernel/vdso.c

@@ -206,11 +206,16 @@ static int aarch32_vdso_mremap(const struct vm_special_mapping *sm,
 #define C_SIGPAGE	1
 #define C_PAGES		(C_SIGPAGE + 1)
 #endif /* CONFIG_COMPAT_VDSO */
-static struct page *aarch32_vdso_pages[C_PAGES] __ro_after_init;
+
+static struct page *aarch32_vectors_page __ro_after_init;
+#ifndef CONFIG_COMPAT_VDSO
+static struct page *aarch32_sig_page __ro_after_init;
+#endif
+
 static struct vm_special_mapping aarch32_vdso_spec[C_PAGES] = {
 	{
 		.name	= "[vectors]", /* ABI */
-		.pages	= &aarch32_vdso_pages[C_VECTORS],
+		.pages	= &aarch32_vectors_page,
 	},
 #ifdef CONFIG_COMPAT_VDSO
 	{
@@ -223,7 +228,7 @@ static struct vm_special_mapping aarch32_vdso_spec[C_PAGES] = {
 #else
 	{
 		.name	= "[sigpage]", /* ABI */
-		.pages	= &aarch32_vdso_pages[C_SIGPAGE],
+		.pages	= &aarch32_sig_page,
 	},
 #endif /* CONFIG_COMPAT_VDSO */
 };
@@ -243,8 +248,8 @@ static int aarch32_alloc_kuser_vdso_page(void)
 
 	memcpy((void *)(vdso_page + 0x1000 - kuser_sz), __kuser_helper_start,
 	       kuser_sz);
-	aarch32_vdso_pages[C_VECTORS] = virt_to_page(vdso_page);
-	flush_dcache_page(aarch32_vdso_pages[C_VECTORS]);
+	aarch32_vectors_page = virt_to_page(vdso_page);
+	flush_dcache_page(aarch32_vectors_page);
 	return 0;
 }
 
@@ -275,8 +280,8 @@ static int __aarch32_alloc_vdso_pages(void)
 		return -ENOMEM;
 
 	memcpy((void *)sigpage, __aarch32_sigret_code_start, sigret_sz);
-	aarch32_vdso_pages[C_SIGPAGE] = virt_to_page(sigpage);
-	flush_dcache_page(aarch32_vdso_pages[C_SIGPAGE]);
+	aarch32_sig_page = virt_to_page(sigpage);
+	flush_dcache_page(aarch32_sig_page);
 
 	ret = aarch32_alloc_kuser_vdso_page();
 	if (ret)