kaiser: add "nokaiser" boot option, using ALTERNATIVE

Added "nokaiser" boot option: an early param like "noinvpcid".
Most places now check int kaiser_enabled (#defined 0 when not
CONFIG_KAISER) instead of #ifdef CONFIG_KAISER; but entry_64.S
and entry_64_compat.S are using the ALTERNATIVE technique, which
patches in the preferred instructions at runtime.  That technique
is tied to x86 cpu features, so X86_FEATURE_KAISER is fabricated.

Prior to "nokaiser", Kaiser #defined _PAGE_GLOBAL 0: revert that,
but be careful with both _PAGE_GLOBAL and CR4.PGE: setting them when
nokaiser like when !CONFIG_KAISER, but not setting either when kaiser -
neither matters on its own, but it's hard to be sure that _PAGE_GLOBAL
won't get set in some obscure corner, or something add PGE into CR4.
By omitting _PAGE_GLOBAL from __supported_pte_mask when kaiser_enabled,
all page table setup which uses pte_pfn() masks it out of the ptes.

It's slightly shameful that the same declaration versus definition of
kaiser_enabled appears in not one, not two, but in three header files
(asm/kaiser.h, asm/pgtable.h, asm/tlbflush.h).  I felt safer that way,
than with #including any of those in any of the others; and did not
feel it worth an asm/kaiser_enabled.h - kernel/cpu/common.c includes
them all, so we shall hear about it if they get out of synch.

Cleanups while in the area: removed the silly #ifdef CONFIG_KAISER
from kaiser.c; removed the unused native_get_normal_pgd(); removed
the spurious reg clutter from SWITCH_*_CR3 macro stubs; corrected some
comments.  But more interestingly, set CR4.PSE in secondary_startup_64:
the manual is clear that it does not matter whether it's 0 or 1 when
4-level-pts are enabled, but I was distracted to find cr4 different on
BSP and auxiliaries - BSP alone was adding PSE, in probe_page_size_mask().

Signed-off-by: Hugh Dickins <hughd@google.com>
Acked-by: Jiri Kosina <jkosina@suse.cz>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

3 files changed, 31 insertions, 4 deletions

diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
index 46ad2faca9ab..86db04f0ec78 100644
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -178,6 +178,20 @@ static int __init x86_pcid_setup(char *s)
 	return 1;
 }
 __setup("nopcid", x86_pcid_setup);
+
+static int __init x86_nokaiser_setup(char *s)
+{
+	/* nokaiser doesn't accept parameters */
+	if (s)
+		return -EINVAL;
+#ifdef CONFIG_KAISER
+	kaiser_enabled = 0;
+	setup_clear_cpu_cap(X86_FEATURE_KAISER);
+	pr_info("nokaiser: KAISER feature disabled\n");
+#endif
+	return 0;
+}
+early_param("nokaiser", x86_nokaiser_setup);
 #endif
 
 static int __init x86_noinvpcid_setup(char *s)
@@ -324,7 +338,7 @@ static __always_inline void setup_smap(struct cpuinfo_x86 *c)
 static void setup_pcid(struct cpuinfo_x86 *c)
 {
 	if (cpu_has(c, X86_FEATURE_PCID)) {
-		if (cpu_has(c, X86_FEATURE_PGE)) {
+		if (cpu_has(c, X86_FEATURE_PGE) || kaiser_enabled) {
 			cr4_set_bits(X86_CR4_PCIDE);
 			/*
 			 * INVPCID has two "groups" of types:
@@ -747,6 +761,10 @@ void get_cpu_cap(struct cpuinfo_x86 *c)
 		c->x86_power = cpuid_edx(0x80000007);
 
 	init_scattered_cpuid_features(c);
+#ifdef CONFIG_KAISER
+	if (kaiser_enabled)
+		set_cpu_cap(c, X86_FEATURE_KAISER);
+#endif
 }
 
 static void identify_cpu_without_cpuid(struct cpuinfo_x86 *c)
@@ -1406,6 +1424,14 @@ void cpu_init(void)
 	 * try to read it.
 	 */
 	cr4_init_shadow();
+	if (!kaiser_enabled) {
+		/*
+		 * secondary_startup_64() deferred setting PGE in cr4:
+		 * probe_page_size_mask() sets it on the boot cpu,
+		 * but it needs to be set on each secondary cpu.
+		 */
+		cr4_set_bits(X86_CR4_PGE);
+	}
 
 	/*
 	 * Load microcode on this cpu if a valid microcode is available.
diff --git a/arch/x86/kernel/espfix_64.c b/arch/x86/kernel/espfix_64.c
index 54de4c70cbd6..b02cb2ec6726 100644
--- a/arch/x86/kernel/espfix_64.c
+++ b/arch/x86/kernel/espfix_64.c
@@ -132,9 +132,10 @@ void __init init_espfix_bsp(void)
 	 * area to ensure it is mapped into the shadow user page
 	 * tables.
 	 */
-	if (IS_ENABLED(CONFIG_KAISER))
+	if (kaiser_enabled) {
 		set_pgd(native_get_shadow_pgd(pgd_p),
 			__pgd(_KERNPG_TABLE | __pa((pud_t *)espfix_pud_page)));
+	}
 
 	/* Randomize the locations */
 	init_espfix_random();
diff --git a/arch/x86/kernel/head_64.S b/arch/x86/kernel/head_64.S
index abbbcfbb5e26..9af949ce8a69 100644
--- a/arch/x86/kernel/head_64.S
+++ b/arch/x86/kernel/head_64.S
@@ -183,8 +183,8 @@ ENTRY(secondary_startup_64)
 	movq	$(init_level4_pgt - __START_KERNEL_map), %rax
 1:
 
-	/* Enable PAE mode and PGE */
-	movl	$(X86_CR4_PAE | X86_CR4_PGE), %ecx
+	/* Enable PAE and PSE, but defer PGE until kaiser_enabled is decided */
+	movl	$(X86_CR4_PAE | X86_CR4_PSE), %ecx
 	movq	%rcx, %cr4
 
 	/* Setup early boot stage 4 level pagetables. */