Patch "kaiser: disabled on Xen PV" has been added to the 4.4-stable tree

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

kaiser: disabled on Xen PV

to the 4.4-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-4.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Jiri Kosina <[email protected]>
Date: Tue, 2 Jan 2018 14:19:49 +0100
Subject: kaiser: disabled on Xen PV

From: Jiri Kosina <[email protected]>

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.

---
 arch/x86/mm/kaiser.c |    5 +++++
 1 file changed, 5 insertions(+)

@@ -264,6 +264,9 @@ 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))

@@ -291,6 +294,8 @@ 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 [email protected] are

queue-4.4/kaiser-vmstat-show-nr_kaisertable-as-nr_overhead.patch queue-4.4/kaiser-add-nokaiser-boot-option-using-alternative.patch queue-4.4/kaiser-fix-unlikely-error-in-alloc_ldt_struct.patch queue-4.4/kaiser-_pgd_alloc-without-__gfp_repeat-to-avoid-stalls.patch queue-4.4/kaiser-kaiser_flush_tlb_on_return_to_user-check-pcid.patch queue-4.4/kaiser-merged-update.patch queue-4.4/kaiser-delete-kaiser_real_switch-option.patch queue-4.4/kaiser-kaiser_remove_mapping-move-along-the-pgd.patch queue-4.4/kaiser-fix-perf-crashes.patch queue-4.4/kaiser-drop-is_atomic-arg-to-kaiser_pagetable_walk.patch queue-4.4/kaiser-load_new_mm_cr3-let-switch_user_cr3-flush-user.patch queue-4.4/kaiser-enhanced-by-kernel-and-user-pcids.patch queue-4.4/kaiser-x86_cr3_pcid_noflush-and-x86_cr3_pcid_user.patch queue-4.4/kaiser-use-alternative-instead-of-x86_cr3_pcid_noflush.patch queue-4.4/kaiser-stack-map-page_size-at-thread_size-page_size.patch queue-4.4/kaiser-name-that-0x1000-kaiser_shadow_pgd_offset.patch queue-4.4/kaiser-fix-regs-to-do_nmi-ifndef-config_kaiser.patch queue-4.4/kaiser-do-not-set-_page_nx-on-pgd_none.patch queue-4.4/kaiser-tidied-up-asm-kaiser.h-somewhat.patch queue-4.4/kaiser-cleanups-while-trying-for-gold-link.patch queue-4.4/kaiser-disabled-on-xen-pv.patch queue-4.4/kaiser-tidied-up-kaiser_add-remove_mapping-slightly.patch queue-4.4/kaiser-fix-build-and-fixme-in-alloc_ldt_struct.patch queue-4.4/kaiser-kernel-address-isolation.patch queue-4.4/kaiser-enomem-if-kaiser_pagetable_walk-null.patch queue-4.4/kaiser-asm-tlbflush.h-handle-nopge-at-lower-level.patch queue-4.4/kaiser-paranoid_entry-pass-cr3-need-to-paranoid_exit.patch queue-4.4/kaiser-kaiser-depends-on-smp.patch queue-4.4/kaiser-pcid-0-for-kernel-and-128-for-user.patch