x86/tlb: Uninline __get_current_cr3_fast()

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.

In preparation for unexporting cpu_tlbstate move __get_current_cr3_fast()
into the x86 TLB management code.

No functional change.

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>
Acked-by: Andy Lutomirski <luto@kernel.org>
Link: https://lkml.kernel.org/r/20200421092558.848064318@linutronix.de

1 files changed, 20 insertions, 0 deletions

diff --git a/arch/x86/mm/tlb.c b/arch/x86/mm/tlb.c
index 66f96f21a7b6..ea6f98a7ec06 100644
--- a/arch/x86/mm/tlb.c
+++ b/arch/x86/mm/tlb.c
@@ -844,6 +844,26 @@ void flush_tlb_kernel_range(unsigned long start, unsigned long end)
 }
 
 /*
+ * This can be used from process context to figure out what the value of
+ * CR3 is without needing to do a (slow) __read_cr3().
+ *
+ * It's intended to be used for code like KVM that sneakily changes CR3
+ * and needs to restore it.  It needs to be used very carefully.
+ */
+unsigned long __get_current_cr3_fast(void)
+{
+	unsigned long cr3 = build_cr3(this_cpu_read(cpu_tlbstate.loaded_mm)->pgd,
+		this_cpu_read(cpu_tlbstate.loaded_mm_asid));
+
+	/* For now, be very restrictive about when this can be called. */
+	VM_WARN_ON(in_nmi() || preemptible());
+
+	VM_BUG_ON(cr3 != __read_cr3());
+	return cr3;
+}
+EXPORT_SYMBOL_GPL(__get_current_cr3_fast);
+
+/*
  * arch_tlbbatch_flush() performs a full TLB flush regardless of the active mm.
  * This means that the 'struct flush_tlb_info' that describes which mappings to
  * flush is actually fixed. We therefore set a single fixed struct and use it in