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, 11 insertions, 0 deletions

diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c
index 9da70b279dad..f2eab49d044e 100644
--- a/arch/x86/kernel/process.c
+++ b/arch/x86/kernel/process.c
@@ -612,6 +612,17 @@ void speculation_ctrl_update_current(void)
 	preempt_enable();
 }
 
+static inline void cr4_toggle_bits_irqsoff(unsigned long mask)
+{
+	unsigned long newval, cr4 = this_cpu_read(cpu_tlbstate.cr4);
+
+	newval = cr4 ^ mask;
+	if (newval != cr4) {
+		this_cpu_write(cpu_tlbstate.cr4, newval);
+		__write_cr4(newval);
+	}
+}
+
 void __switch_to_xtra(struct task_struct *prev_p, struct task_struct *next_p)
 {
 	unsigned long tifp, tifn;