x86/asm: Get rid of __read_cr4_safe()

We use __read_cr4() vs __read_cr4_safe() inconsistently.  On
CR4-less CPUs, all CR4 bits are effectively clear, so we can make
the code simpler and more robust by making __read_cr4() always fix
up faults on 32-bit kernels.

This may fix some bugs on old 486-like CPUs, but I don't have any
easy way to test that.

Signed-off-by: Andy Lutomirski <luto@kernel.org>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: david@saggiorato.net
Link: http://lkml.kernel.org/r/ea647033d357d9ce2ad2bbde5a631045f5052fb6.1475178370.git.luto@kernel.org
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

arch/x86/kernel/paravirt.c

@@ -332,7 +332,6 @@ __visible struct pv_cpu_ops pv_cpu_ops = {
 	.read_cr0 = native_read_cr0,
 	.write_cr0 = native_write_cr0,
 	.read_cr4 = native_read_cr4,
-	.read_cr4_safe = native_read_cr4_safe,
 	.write_cr4 = native_write_cr4,
 #ifdef CONFIG_X86_64
 	.read_cr8 = native_read_cr8,

arch/x86/kernel/process_32.c

@@ -90,7 +90,7 @@ void __show_regs(struct pt_regs *regs, int all)
 	cr0 = read_cr0();
 	cr2 = read_cr2();
 	cr3 = read_cr3();
-	cr4 = __read_cr4_safe();
+	cr4 = __read_cr4();
 	printk(KERN_DEFAULT "CR0: %08lx CR2: %08lx CR3: %08lx CR4: %08lx\n",
 			cr0, cr2, cr3, cr4);
 

arch/x86/kernel/setup.c

@@ -1137,7 +1137,7 @@ void __init setup_arch(char **cmdline_p)
 	 * auditing all the early-boot CR4 manipulation would be needed to
 	 * rule it out.
 	 */
-	mmu_cr4_features = __read_cr4_safe();
+	mmu_cr4_features = __read_cr4();
 
 	memblock_set_current_limit(get_max_mapped());