mm: huge_memory: don't force huge page alignment on 32 bit

commit efa7df3 ("mm: align larger anonymous mappings on THP
boundaries") caused two issues [1] [2] reported on 32 bit system or compat
userspace.

It doesn't make too much sense to force huge page alignment on 32 bit
system due to the constrained virtual address space.

[1] https://lore.kernel.org/linux-mm/[email protected]/
[2] https://lore.kernel.org/linux-mm/CAJuCfpHXLdQy1a2B6xN2d7quTYwg2OoZseYPZTRpU0eHHKD-sQ@mail.gmail.com/

Link: https://lkml.kernel.org/r/[email protected]
Fixes: efa7df3 ("mm: align larger anonymous mappings on THP boundaries")
Signed-off-by: Yang Shi <[email protected]>
Reported-by: Jiri Slaby <[email protected]>
Reported-by: Suren Baghdasaryan <[email protected]>
Tested-by: Jiri Slaby <[email protected]>
Tested-by: Suren Baghdasaryan <[email protected]>
Reviewed-by: Matthew Wilcox (Oracle) <[email protected]>
Cc: Rik van Riel <[email protected]>
Cc: Christopher Lameter <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

Author: Yang Shi

mm/huge_memory.c

@@ -37,6 +37,7 @@
 #include <linux/page_owner.h>
 #include <linux/sched/sysctl.h>
 #include <linux/memory-tiers.h>
+#include <linux/compat.h>
 
 #include <asm/tlb.h>
 #include <asm/pgalloc.h>
@@ -811,6 +812,9 @@ static unsigned long __thp_get_unmapped_area(struct file *filp,
 	loff_t off_align = round_up(off, size);
 	unsigned long len_pad, ret;
 
+	if (IS_ENABLED(CONFIG_32BIT) || in_compat_syscall())
+		return 0;
+
 	if (off_end <= off_align || (off_end - off_align) < size)
 		return 0;