Patch "powerpc/64s: Support disabling RFI flush with no_rfi_flush and nopti" 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

    powerpc/64s: Support disabling RFI flush with no_rfi_flush and nopti

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:
     powerpc-64s-support-disabling-rfi-flush-with-no_rfi_flush-and-nopti.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 bc9c9304a45480797e13a8e1df96ffcf44fb62fe Mon Sep 17 00:00:00 2001
From: Michael Ellerman <mpe@ellerman.id.au>
Date: Wed, 10 Jan 2018 03:07:15 +1100
Subject: powerpc/64s: Support disabling RFI flush with no_rfi_flush and nopti

From: Michael Ellerman <mpe@ellerman.id.au>

commit bc9c9304a45480797e13a8e1df96ffcf44fb62fe upstream.

Because there may be some performance overhead of the RFI flush, add
kernel command line options to disable it.

We add a sensibly named 'no_rfi_flush' option, but we also hijack the
x86 option 'nopti'. The RFI flush is not the same as KPTI, but if we
see 'nopti' we can guess that the user is trying to avoid any overhead
of Meltdown mitigations, and it means we don't have to educate every
one about a different command line option.

Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 arch/powerpc/kernel/setup_64.c |   24 +++++++++++++++++++++++-
 1 file changed, 23 insertions(+), 1 deletion(-)

--- a/arch/powerpc/kernel/setup_64.c
+++ b/arch/powerpc/kernel/setup_64.c
@@ -682,8 +682,29 @@ early_initcall(disable_hardlockup_detect
 #ifdef CONFIG_PPC_BOOK3S_64
 static enum l1d_flush_type enabled_flush_types;
 static void *l1d_flush_fallback_area;
+static bool no_rfi_flush;
 bool rfi_flush;
 
+static int __init handle_no_rfi_flush(char *p)
+{
+	pr_info("rfi-flush: disabled on command line.");
+	no_rfi_flush = true;
+	return 0;
+}
+early_param("no_rfi_flush", handle_no_rfi_flush);
+
+/*
+ * The RFI flush is not KPTI, but because users will see doco that says to use
+ * nopti we hijack that option here to also disable the RFI flush.
+ */
+static int __init handle_no_pti(char *p)
+{
+	pr_info("rfi-flush: disabling due to 'nopti' on command line.\n");
+	handle_no_rfi_flush(NULL);
+	return 0;
+}
+early_param("nopti", handle_no_pti);
+
 static void do_nothing(void *unused)
 {
 	/*
@@ -754,7 +775,8 @@ void __init setup_rfi_flush(enum l1d_flu
 
 	enabled_flush_types = types;
 
-	rfi_flush_enable(enable);
+	if (!no_rfi_flush)
+		rfi_flush_enable(enable);
 }
 #endif /* CONFIG_PPC_BOOK3S_64 */
 #endif


Patches currently in stable-queue which might be from mpe@ellerman.id.au are

queue-4.9/powerpc-64-add-macros-for-annotating-the-destination-of-rfid-hrfid.patch
queue-4.9/powerpc-pseries-add-h_get_cpu_characteristics-flags-wrapper.patch
queue-4.9/powerpc-64s-allow-control-of-rfi-flush-via-debugfs.patch
queue-4.9/powerpc-powernv-check-device-tree-for-rfi-flush-settings.patch
queue-4.9/powerpc-64s-convert-slb_miss_common-to-use-rfi_to_user-kernel.patch
queue-4.9/powerpc-64s-support-disabling-rfi-flush-with-no_rfi_flush-and-nopti.patch
queue-4.9/powerpc-64-convert-the-syscall-exit-path-to-use-rfi_to_user-kernel.patch
queue-4.9/powerpc-64s-add-support-for-rfi-flush-of-l1-d-cache.patch
queue-4.9/powerpc-pseries-query-hypervisor-for-rfi-flush-settings.patch
queue-4.9/powerpc-64-convert-fast_exception_return-to-use-rfi_to_user-kernel.patch
queue-4.9/powerpc-64s-wire-up-cpu_show_meltdown.patch