[patch 35/60] x86/espfix: Ensure that ESPFIX is visible in user PGD

[Thomas Gleixner]

From: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>

Clone the ESPFIX alias mapping area so the entry/exit code has access to it
even with the user space page tables.

[ tglx: Remove the per cpu user mapped oddity ]

Signed-off-by: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>

---
 arch/x86/kernel/espfix_64.c |   16 ++++++++++++++++
 1 file changed, 16 insertions(+)

--- a/arch/x86/kernel/espfix_64.c
+++ b/arch/x86/kernel/espfix_64.c
@@ -129,6 +129,22 @@ void __init init_espfix_bsp(void)
 	p4d = p4d_alloc(&init_mm, pgd, ESPFIX_BASE_ADDR);
 	p4d_populate(&init_mm, p4d, espfix_pud_page);
 
+	/*
+	 * Just copy the top-level PGD that is mapping the espfix area to
+	 * ensure it is mapped into the user page tables.
+	 *
+	 * For 5-level paging, the espfix pgd was populated when
+	 * kpti_init() pre-populated all the pgd entries.  The above
+	 * p4d_alloc() would never do anything and the p4d_populate() would
+	 * be done to a p4d already mapped in the userspace pgd.
+	 */
+#ifdef CONFIG_KERNEL_PAGE_TABLE_ISOLATION
+	if (CONFIG_PGTABLE_LEVELS <= 4) {
+		set_pgd(kernel_to_user_pgdp(pgd),
+			__pgd(_KERNPG_TABLE | (p4d_pfn(*p4d) << PAGE_SHIFT)));
+	}
+#endif
+
 	/* Randomize the locations */
 	init_espfix_random();