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%3Ba=su...

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