mips: vdso: prefer do_mmap() to mmap_region()

Patch series "mm: update mips to use do_mmap(), make mmap_region()
internal".

Currently the only user of mmap_region() outside of the memory management
code is the MIPS VDSO implementation.

This uses mmap_region() to map a 'delay slot emulation page' at the top of
the stack which is read-only and executable.

This mapping requires that an already-acquired mmap write lock is utilised
and that uffd and populate logic is ignored. This rules out vm_mmap(),
however do_mmap() fits the bill.

Adapt this code to use do_mmap() and then once done, make mmap_region()
internal and userland testable, and avoid any other uses of mmap_region(),
which is absolutely and strictly an internal mm function which bypasses a
great number of checks and logic.


This patch (of 2):

mmap_region() is an internal memory management implementation detail that
is not intended to be used outside of the memory management subsystem.

Map the delay slot emulation page using do_mmap() which makes use of the
already-held mmap write lock and bypasses unneeded populate and
userfaultfd logic.

This should have the precise same behaviour as the existing logic.

Link: https://lkml.kernel.org/r/cover.1735819274.git.lorenzo.stoakes@oracle.com
Link: https://lkml.kernel.org/r/ef076e381570f709e5c2c142dc030ec5b3309a0e.1735819274.git.lorenzo.stoakes@oracle.com
Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Reviewed-by: Liam R. Howlett <Liam.Howlett@Oracle.com>
Cc: Jann Horn <jannh@google.com>
Cc: Thomas Bogendoerfer <tsbogend@alpha.franken.de>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

arch/mips/kernel/vdso.c

@@ -11,6 +11,7 @@
 #include <linux/ioport.h>
 #include <linux/kernel.h>
 #include <linux/mm.h>
+#include <linux/mman.h>
 #include <linux/random.h>
 #include <linux/sched.h>
 #include <linux/slab.h>
@@ -97,11 +98,12 @@ int arch_setup_additional_pages(struct linux_binprm *bprm, int uses_interp)
 		return -EINTR;
 
 	if (IS_ENABLED(CONFIG_MIPS_FP_SUPPORT)) {
+		unsigned long unused;
+
 		/* Map delay slot emulation page */
-		base = mmap_region(NULL, STACK_TOP, PAGE_SIZE,
-				VM_READ | VM_EXEC |
-				VM_MAYREAD | VM_MAYWRITE | VM_MAYEXEC,
-				0, NULL);
+		base = do_mmap(NULL, STACK_TOP, PAGE_SIZE, PROT_READ | PROT_EXEC,
+			       MAP_ANONYMOUS | MAP_PRIVATE | MAP_FIXED, 0, 0, &unused,
+			       NULL);
 		if (IS_ERR_VALUE(base)) {
 			ret = base;
 			goto out;