x86/cpu: Uninline CR4 accessors

cpu_tlbstate is exported because various TLB-related functions need
access to it, but cpu_tlbstate is sensitive information which should
only be accessed by well-contained kernel functions and not be directly
exposed to modules.

The various CR4 accessors require cpu_tlbstate as the CR4 shadow cache
is located there.

In preparation for unexporting cpu_tlbstate, create a builtin function
for manipulating CR4 and rework the various helpers to use it.

No functional change.

 [ bp: push the export of native_write_cr4() only when CONFIG_LKTDM=m to
   the last patch in the series. ]

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Borislav Petkov <bp@suse.de>
Reviewed-by: Alexandre Chartre <alexandre.chartre@oracle.com>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20200421092558.939985695@linutronix.de

1 files changed, 22 insertions, 1 deletions

diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
index bed0cb83fe24..82042f40fc45 100644
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -387,7 +387,28 @@ set_register:
 			  bits_missing);
 	}
 }
-EXPORT_SYMBOL(native_write_cr4);
+EXPORT_SYMBOL_GPL(native_write_cr4);
+
+void cr4_update_irqsoff(unsigned long set, unsigned long clear)
+{
+	unsigned long newval, cr4 = this_cpu_read(cpu_tlbstate.cr4);
+
+	lockdep_assert_irqs_disabled();
+
+	newval = (cr4 & ~clear) | set;
+	if (newval != cr4) {
+		this_cpu_write(cpu_tlbstate.cr4, newval);
+		__write_cr4(newval);
+	}
+}
+EXPORT_SYMBOL(cr4_update_irqsoff);
+
+/* Read the CR4 shadow. */
+unsigned long cr4_read_shadow(void)
+{
+	return this_cpu_read(cpu_tlbstate.cr4);
+}
+EXPORT_SYMBOL_GPL(cr4_read_shadow);
 
 void cr4_init(void)
 {