[PATCH 2/6] x86/cpu: drop wp_works_ok member of struct cpuinfo_x86

From: Mathias Krause <minipli@googlemail.com>
To: Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@redhat.com>, "H. Peter Anvin" <hpa@zytor.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
	Borislav Petkov <bp@alien8.de>,
	"David S. Miller" <davem@davemloft.net>,
	Jesper Nilsson <jesper.nilsson@axis.com>,
	Mikael Starvik <starvik@axis.com>,
	Geert Uytterhoeven <geert@linux-m68k.org>,
	x86@kernel.org, linux-kernel@vger.kernel.org,
	Mathias Krause <minipli@googlemail.com>,
	"H. Peter Anvin" <hpa@linux.intel.com>,
	Arnd Hannemann <hannemann@nets.rwth-aachen.de>,
	Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
Subject: [PATCH 2/6] x86/cpu: drop wp_works_ok member of struct cpuinfo_x86
Date: Sun, 12 Feb 2017 22:12:08 +0100	[thread overview]
Message-ID: <1486933932-585-3-git-send-email-minipli@googlemail.com> (raw)
In-Reply-To: <1486933932-585-1-git-send-email-minipli@googlemail.com>

Remove the wp_works_ok member of struct cpuinfo_x86. It's an
optimization back from Linux v0.99 times where we had no fixup support
yet and did the CR0.WP test via special code in the page fault handler.
The < 0 test was an optimization to not do the special casing for each
NULL ptr access violation but just for the first one doing the WP test.
Today it serves no real purpose as the test no longer needs special code
in the page fault handler and the only call side -- mem_init() -- calls
it just once, anyway. However, Xen pre-initializes it to 1, to skip the
test.

Doing the test again for Xen should be no issue at all, as even the
commit introducing skipping the test (commit d560bc61575e ("x86, xen:
Suppress WP test on Xen")) mentioned it being ban aid only. And, in
fact, testing the patch on Xen showed nothing breaks.

The pre-fixup times are long gone and with the removal of the fallback
handling code in commit a5c2a893dbd4 ("x86, 386 removal: Remove
CONFIG_X86_WP_WORKS_OK") the kernel requires a working CR0.WP anyway.
So just get rid of the "optimization" and do the test unconditionally.

Cc: Borislav Petkov <bp@alien8.de>
Cc: H. Peter Anvin <hpa@linux.intel.com>
Cc: Arnd Hannemann <hannemann@nets.rwth-aachen.de>
Cc: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
Signed-off-by: Mathias Krause <minipli@googlemail.com>
---
 arch/x86/include/asm/processor.h |    4 +---
 arch/x86/kernel/cpu/proc.c       |    5 ++---
 arch/x86/kernel/setup.c          |   11 ++++-------
 arch/x86/mm/init_32.c            |    9 +++++----
 arch/x86/xen/enlighten.c         |    1 -
 5 files changed, 12 insertions(+), 18 deletions(-)

diff --git a/arch/x86/include/asm/processor.h b/arch/x86/include/asm/processor.h
index bf7cb1e00ce7..7b15b29e8a66 100644
--- a/arch/x86/include/asm/processor.h
+++ b/arch/x86/include/asm/processor.h
@@ -89,9 +89,7 @@ struct cpuinfo_x86 {
 	__u8			x86_vendor;	/* CPU vendor */
 	__u8			x86_model;
 	__u8			x86_mask;
-#ifdef CONFIG_X86_32
-	char			wp_works_ok;	/* It doesn't on 386's */
-#else
+#ifdef CONFIG_X86_64
 	/* Number of 4K pages in DTLB/ITLB combined(in pages): */
 	int			x86_tlbsize;
 #endif
diff --git a/arch/x86/kernel/cpu/proc.c b/arch/x86/kernel/cpu/proc.c
index 18ca99f2798b..6df621ae62a7 100644
--- a/arch/x86/kernel/cpu/proc.c
+++ b/arch/x86/kernel/cpu/proc.c
@@ -31,14 +31,13 @@ static void show_cpuinfo_misc(struct seq_file *m, struct cpuinfo_x86 *c)
 		   "fpu\t\t: %s\n"
 		   "fpu_exception\t: %s\n"
 		   "cpuid level\t: %d\n"
-		   "wp\t\t: %s\n",
+		   "wp\t\t: yes\n",
 		   static_cpu_has_bug(X86_BUG_FDIV) ? "yes" : "no",
 		   static_cpu_has_bug(X86_BUG_F00F) ? "yes" : "no",
 		   static_cpu_has_bug(X86_BUG_COMA) ? "yes" : "no",
 		   static_cpu_has(X86_FEATURE_FPU) ? "yes" : "no",
 		   static_cpu_has(X86_FEATURE_FPU) ? "yes" : "no",
-		   c->cpuid_level,
-		   c->wp_works_ok ? "yes" : "no");
+		   c->cpuid_level);
 }
 #else
 static void show_cpuinfo_misc(struct seq_file *m, struct cpuinfo_x86 *c)
diff --git a/arch/x86/kernel/setup.c b/arch/x86/kernel/setup.c
index 4cfba947d774..ffc2791ab256 100644
--- a/arch/x86/kernel/setup.c
+++ b/arch/x86/kernel/setup.c
@@ -173,14 +173,11 @@ int default_check_phys_apicid_present(int phys_apicid)
 
 
 #ifdef CONFIG_X86_32
-/* cpu data as detected by the assembly code in head.S */
-struct cpuinfo_x86 new_cpu_data = {
-	.wp_works_ok = -1,
-};
+/* cpu data as detected by the assembly code in head_32.S */
+struct cpuinfo_x86 new_cpu_data;
+
 /* common cpu data for all cpus */
-struct cpuinfo_x86 boot_cpu_data __read_mostly = {
-	.wp_works_ok = -1,
-};
+struct cpuinfo_x86 boot_cpu_data __read_mostly;
 EXPORT_SYMBOL(boot_cpu_data);
 
 unsigned int def_to_bigsmp;
diff --git a/arch/x86/mm/init_32.c b/arch/x86/mm/init_32.c
index 928d657de829..e0fd0c8b9ad1 100644
--- a/arch/x86/mm/init_32.c
+++ b/arch/x86/mm/init_32.c
@@ -716,15 +716,17 @@ void __init paging_init(void)
  */
 static void __init test_wp_bit(void)
 {
+	int wp_works_ok;
+
 	printk(KERN_INFO
   "Checking if this processor honours the WP bit even in supervisor mode...");
 
 	/* Any page-aligned address will do, the test is non-destructive */
 	__set_fixmap(FIX_WP_TEST, __pa(&swapper_pg_dir), PAGE_KERNEL_RO);
-	boot_cpu_data.wp_works_ok = do_test_wp_bit();
+	wp_works_ok = do_test_wp_bit();
 	clear_fixmap(FIX_WP_TEST);
 
-	if (!boot_cpu_data.wp_works_ok) {
+	if (!wp_works_ok) {
 		printk(KERN_CONT "No.\n");
 		panic("Linux doesn't support CPUs with broken WP.");
 	} else {
@@ -811,8 +813,7 @@ void __init mem_init(void)
 	BUG_ON(VMALLOC_START				>= VMALLOC_END);
 	BUG_ON((unsigned long)high_memory		> VMALLOC_START);
 
-	if (boot_cpu_data.wp_works_ok < 0)
-		test_wp_bit();
+	test_wp_bit();
 }
 
 #ifdef CONFIG_MEMORY_HOTPLUG
diff --git a/arch/x86/xen/enlighten.c b/arch/x86/xen/enlighten.c
index 51ef95232725..f37b297bdedc 100644
--- a/arch/x86/xen/enlighten.c
+++ b/arch/x86/xen/enlighten.c
@@ -1682,7 +1682,6 @@ asmlinkage __visible void __init xen_start_kernel(void)
 	/* set up basic CPUID stuff */
 	cpu_detect(&new_cpu_data);
 	set_cpu_cap(&new_cpu_data, X86_FEATURE_FPU);
-	new_cpu_data.wp_works_ok = 1;
 	new_cpu_data.x86_capability[CPUID_1_EDX] = cpuid_edx(1);
 #endif
 
-- 
1.7.10.4
