svn commit: r346996 - head/sys/arm64/arm64

[Andrew Turner]

Author: andrew
Date: Wed May  1 17:12:49 2019
New Revision: 346996
URL: https://svnweb.freebsd.org/changeset/base/346996

Log:
  Restore x18 in efi_arch_leave.
  
  Some UEFI implementations trash this register and, as we use it as a
  platform register, the kernel doesn't save it before calling into the UEFI
  runtime services. As we have a copy in tpidr_el1 restore from there when
  exiting the EFI environment.
  
  PR:		237234, 237055
  Reviewed by:	manu
  Tested On:	Ampere eMAG
  MFC after:	2 weeks
  Sponsored by:	DARPA, AFRL
  Sponsored by:	Ampere Computing (hardware)
  Differential Revision:	https://reviews.freebsd.org/D20127

Modified:
  head/sys/arm64/arm64/efirt_machdep.c

Modified: head/sys/arm64/arm64/efirt_machdep.c
==============================================================================
--- head/sys/arm64/arm64/efirt_machdep.c	Wed May  1 15:28:23 2019	(r346995)
+++ head/sys/arm64/arm64/efirt_machdep.c	Wed May  1 17:12:49 2019	(r346996)
@@ -259,6 +259,16 @@ efi_arch_leave(void)
 {
 	struct thread *td;
 
+	/*
+	 * Restore the pcpu pointer. Some UEFI implementations trash it and
+	 * we don't store it before calling into them. To fix this we need
+	 * to restore it after returning to the kernel context. As reading
+	 * curthread will access x18 we need to restore it before loading
+	 * the thread pointer.
+	 */
+	__asm __volatile(
+	    "mrs x18, tpidr_el1	\n"
+	);
 	td = curthread;
 	__asm __volatile(
 	    "msr ttbr0_el1, %0	\n"