[patch 39/60] x86/mm/kpti: Share cpu_entry_area PMDs

[Thomas Gleixner]

From: Andy Lutomirski <luto@xxxxxxxxxx>

Share the FIX_USR_SHARED PMDs so the user space and kernel space page
tables have the same PMD page.

[ tglx: Made it use the FIX_USR_SHARED range so later additions
  	are covered automatically ]

Signed-off-by: Andy Lutomirski <luto@xxxxxxxxxx>
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
---
 arch/x86/mm/kpti.c |   18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

--- a/arch/x86/mm/kpti.c
+++ b/arch/x86/mm/kpti.c
@@ -167,6 +167,23 @@ kpti_clone_pmds(unsigned long start, uns
 }
 
 /*
+ * Clone the populated PMDs of the user shared fixmaps into the user space
+ * visible page table.
+ */
+static void __init kpti_clone_user_shared(void)
+{
+	unsigned long bot, top;
+
+	bot = __fix_to_virt(FIX_USR_SHARED_BOTTOM);
+	top = __fix_to_virt(FIX_USR_SHARED_TOP) + PAGE_SIZE;
+
+	/* Top of the user shared block must be PMD-aligned. */
+	WARN_ON(top & ~PMD_MASK);
+
+	kpti_clone_pmds(bot, top, 0);
+}
+
+/*
  * Ensure that the top level of the user page tables are entirely
  * populated.  This ensures that all processes that get forked have the
  * same entries.  This way, we do not have to ever go set up new entries in
@@ -216,4 +233,5 @@ void __init kpti_init(void)
 	pr_info("enabled\n");
 
 	kpti_init_all_pgds();
+	kpti_clone_user_shared();
 }