kaiser: delete KAISER_REAL_SWITCH option

We fail to see what CONFIG_KAISER_REAL_SWITCH is for: it seems to be
left over from early development, and now just obscures tricky parts
of the code.  Delete it before adding PCIDs, or nokaiser boot option.

(Or if there is some good reason to keep the option, then it needs
a help text - and a "depends on KAISER", so that all those without
KAISER are not asked the question.)
Acked-by: Jiri Kosina <jkosina@suse.cz>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

CVE-2017-5754
Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>

arch/x86/entry/entry_64.S

@@ -1291,9 +1291,7 @@ ENTRY(nmi)
 	/* %rax is saved above, so OK to clobber here */
 	movq	%cr3, %rax
 	pushq	%rax
-#ifdef CONFIG_KAISER_REAL_SWITCH
 	andq	$(~KAISER_SHADOW_PGD_OFFSET), %rax
-#endif
 	movq	%rax, %cr3
 #endif
 	call	do_nmi
@@ -1534,9 +1532,7 @@ end_repeat_nmi:
 	/* %rax is saved above, so OK to clobber here */
 	movq	%cr3, %rax
 	pushq	%rax
-#ifdef CONFIG_KAISER_REAL_SWITCH
 	andq	$(~KAISER_SHADOW_PGD_OFFSET), %rax
-#endif
 	movq	%rax, %cr3
 #endif
 

arch/x86/include/asm/kaiser.h

@@ -21,17 +21,13 @@
 
 .macro _SWITCH_TO_KERNEL_CR3 reg
 movq %cr3, \reg
-#ifdef CONFIG_KAISER_REAL_SWITCH
 andq $(~KAISER_SHADOW_PGD_OFFSET), \reg
-#endif
 movq \reg, %cr3
 .endm
 
 .macro _SWITCH_TO_USER_CR3 reg
 movq %cr3, \reg
-#ifdef CONFIG_KAISER_REAL_SWITCH
 orq $(KAISER_SHADOW_PGD_OFFSET), \reg
-#endif
 movq \reg, %cr3
 .endm
 

security/Kconfig

@@ -41,10 +41,6 @@ config KAISER
 
 	  If you are unsure how to answer this question, answer Y.
 
-config KAISER_REAL_SWITCH
-	bool "KAISER: actually switch page tables"
-	default y
-
 config SECURITYFS
 	bool "Enable the securityfs filesystem"
 	help