x86/mm: Cleanup the control_va_addr_alignment() __setup handler

Clean up control_va_addr_alignment():

a. Make '=' required instead of optional (as documented).
b. Print a warning if an invalid option value is used.
c. Return 1 from the __setup handler when an invalid option value is
   used. This prevents the kernel from polluting init's (limited)
   environment space with the entire string.

Fixes: dfb09f9b ("x86, amd: Avoid cache aliasing penalties on AMD family 15h")
Reported-by: Igor Zhbanov <i.zhbanov@omprussia.ru>
Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lore.kernel.org/r/64644a2f-4a20-bab3-1e15-3b2cdd0defe3@omprussia.ru
Link: https://lore.kernel.org/r/20220315001045.7680-1-rdunlap@infradead.org

arch/x86/kernel/sys_x86_64.c

@@ -68,9 +68,6 @@ static int __init control_va_addr_alignment(char *str)
 	if (*str == 0)
 		return 1;
 
-	if (*str == '=')
-		str++;
-
 	if (!strcmp(str, "32"))
 		va_align.flags = ALIGN_VA_32;
 	else if (!strcmp(str, "64"))
@@ -80,11 +77,11 @@ static int __init control_va_addr_alignment(char *str)
 	else if (!strcmp(str, "on"))
 		va_align.flags = ALIGN_VA_32 | ALIGN_VA_64;
 	else
-		return 0;
+		pr_warn("invalid option value: 'align_va_addr=%s'\n", str);
 
 	return 1;
 }
-__setup("align_va_addr", control_va_addr_alignment);
+__setup("align_va_addr=", control_va_addr_alignment);
 
 SYSCALL_DEFINE6(mmap, unsigned long, addr, unsigned long, len,
 		unsigned long, prot, unsigned long, flags,