Patch "x86/mm/64: Fix reboot interaction with CR4.PCIDE" has been added to the 4.9-stable tree

[<gregkh@linuxfoundation.org>]

This is a note to let you know that I've just added the patch titled

    x86/mm/64: Fix reboot interaction with CR4.PCIDE

to the 4.9-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     x86-mm-64-fix-reboot-interaction-with-cr4.pcide.patch
and it can be found in the queue-4.9 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@vger.kernel.org> know about it.


>From 924c6b900cfdf376b07bccfd80e62b21914f8a5a Mon Sep 17 00:00:00 2001
From: Andy Lutomirski <luto@kernel.org>
Date: Sun, 8 Oct 2017 21:53:05 -0700
Subject: x86/mm/64: Fix reboot interaction with CR4.PCIDE

From: Andy Lutomirski <luto@kernel.org>

commit 924c6b900cfdf376b07bccfd80e62b21914f8a5a upstream.

Trying to reboot via real mode fails with PCID on: long mode cannot
be exited while CR4.PCIDE is set.  (No, I have no idea why, but the
SDM and actual CPUs are in agreement here.)  The result is a GPF and
a hang instead of a reboot.

I didn't catch this in testing because neither my computer nor my VM
reboots this way.  I can trigger it with reboot=bios, though.

Fixes: 660da7c9228f ("x86/mm: Enable CR4.PCIDE on supported systems")
Reported-and-tested-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Signed-off-by: Andy Lutomirski <luto@kernel.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Borislav Petkov <bp@alien8.de>
Link: https://lkml.kernel.org/r/f1e7d965998018450a7a70c2823873686a8b21c0.1507524746.git.luto@kernel.org
Cc: Hugh Dickins <hughd@google.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 arch/x86/kernel/reboot.c |    4 ++++
 1 file changed, 4 insertions(+)

--- a/arch/x86/kernel/reboot.c
+++ b/arch/x86/kernel/reboot.c
@@ -106,6 +106,10 @@ void __noreturn machine_real_restart(uns
 	load_cr3(initial_page_table);
 #else
 	write_cr3(real_mode_header->trampoline_pgd);
+
+	/* Exiting long mode will fail if CR4.PCIDE is set. */
+	if (static_cpu_has(X86_FEATURE_PCID))
+		cr4_clear_bits(X86_CR4_PCIDE);
 #endif
 
 	/* Jump to the identity-mapped low memory code */


Patches currently in stable-queue which might be from luto@kernel.org are

queue-4.9/x86-vm86-32-switch-to-flush_tlb_mm_range-in-mark_screen_rdonly.patch
queue-4.9/x86-mm-add-the-nopcid-boot-option-to-turn-off-pcid.patch
queue-4.9/x86-mm-enable-cr4.pcide-on-supported-systems.patch
queue-4.9/x86-mm-remove-the-up-asm-tlbflush.h-code-always-use-the-formerly-smp-code.patch
queue-4.9/x86-mm-reimplement-flush_tlb_page-using-flush_tlb_mm_range.patch
queue-4.9/x86-mm-make-flush_tlb_mm_range-more-predictable.patch
queue-4.9/x86-mm-remove-flush_tlb-and-flush_tlb_current_task.patch
queue-4.9/x86-mm-disable-pcid-on-32-bit-kernels.patch
queue-4.9/x86-mm-64-fix-reboot-interaction-with-cr4.pcide.patch