Patch "kaiser: disabled on Xen PV" has been added to the 4.9-stable tree

Patch "kaiser: disabled on Xen PV" has been added to the 4.9-stable tree

[gregkh]

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

    kaiser: disabled on Xen PV

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:
     kaiser-disabled-on-xen-pv.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 foo@baz Wed Jan  3 20:37:21 CET 2018
From: Jiri Kosina <jkosina@suse.cz>
Date: Tue, 2 Jan 2018 14:19:49 +0100
Subject: kaiser: disabled on Xen PV

From: Jiri Kosina <jkosina@suse.cz>


Kaiser cannot be used on paravirtualized MMUs (namely reading and writing CR3).
This does not work with KAISER as the CR3 switch from and to user space PGD
would require to map the whole XEN_PV machinery into both.

More importantly, enabling KAISER on Xen PV doesn't make too much sense, as PV
guests use distinct %cr3 values for kernel and user already.

Signed-off-by: Jiri Kosina <jkosina@suse.cz>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 arch/x86/mm/kaiser.c |    5 +++++
 1 file changed, 5 insertions(+)

--- a/arch/x86/mm/kaiser.c
+++ b/arch/x86/mm/kaiser.c
@@ -263,6 +263,9 @@ void __init kaiser_check_boottime_disabl
 	char arg[5];
 	int ret;
 
+	if (boot_cpu_has(X86_FEATURE_XENPV))
+		goto silent_disable;
+
 	ret = cmdline_find_option(boot_command_line, "pti", arg, sizeof(arg));
 	if (ret > 0) {
 		if (!strncmp(arg, "on", 2))
@@ -290,6 +293,8 @@ enable:
 
 disable:
 	pr_info("Kernel/User page tables isolation: disabled\n");
+
+silent_disable:
 	kaiser_enabled = 0;
 	setup_clear_cpu_cap(X86_FEATURE_KAISER);
 }


Patches currently in stable-queue which might be from jkosina@suse.cz are

queue-4.9/kaiser-add-nokaiser-boot-option-using-alternative.patch
queue-4.9/kaiser-kaiser_flush_tlb_on_return_to_user-check-pcid.patch
queue-4.9/kaiser-drop-is_atomic-arg-to-kaiser_pagetable_walk.patch
queue-4.9/kaiser-use-alternative-instead-of-x86_cr3_pcid_noflush.patch
queue-4.9/kaiser-disabled-on-xen-pv.patch
queue-4.9/kaiser-kernel-address-isolation.patch
queue-4.9/kaiser-asm-tlbflush.h-handle-nopge-at-lower-level.patch