Patch "powerpc/kernel: Fix FP and vector register restoration" has been added to the 4.9-stable tree

Patch "powerpc/kernel: Fix FP and vector register restoration" 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

    powerpc/kernel: Fix FP and vector register restoration

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-kernel-fix-fp-and-vector-register-restoration.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 1195892c091a15cc862f4e202482a36adc924e12 Mon Sep 17 00:00:00 2001
From: Breno Leitao <leitao@debian.org>
Date: Fri, 2 Jun 2017 18:43:30 -0300
Subject: powerpc/kernel: Fix FP and vector register restoration

From: Breno Leitao <leitao@debian.org>

commit 1195892c091a15cc862f4e202482a36adc924e12 upstream.

Currently tsk->thread->load_vec and load_fp are not initialized during
task creation, which can lead to garbage values in these variables (non-zero
values).

These variables will be checked later in restore_math() to validate if the
FP and vector registers are being utilized. Since these values might be
non-zero, the restore_math() will continue to save the FP and vectors even if
they were never utilized by the userspace application. load_fp and load_vec
counters will then overflow (they wrap at 255) and the FP and Altivec will be
finally disabled, but before that condition is reached (counter overflow)
several context switches will have restored FP and vector registers without
need, causing a performance degradation.

Fixes: 70fe3d980f5f ("powerpc: Restore FPU/VEC/VSX if previously used")
Signed-off-by: Breno Leitao <leitao@debian.org>
Signed-off-by: Gustavo Romero <gusbromero@gmail.com>
Acked-by: Anton Blanchard <anton@samba.org>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 arch/powerpc/kernel/process.c |    2 ++
 1 file changed, 2 insertions(+)

--- a/arch/powerpc/kernel/process.c
+++ b/arch/powerpc/kernel/process.c
@@ -1659,6 +1659,7 @@ void start_thread(struct pt_regs *regs,
 #ifdef CONFIG_VSX
 	current->thread.used_vsr = 0;
 #endif
+	current->thread.load_fp = 0;
 	memset(&current->thread.fp_state, 0, sizeof(current->thread.fp_state));
 	current->thread.fp_save_area = NULL;
 #ifdef CONFIG_ALTIVEC
@@ -1667,6 +1668,7 @@ void start_thread(struct pt_regs *regs,
 	current->thread.vr_save_area = NULL;
 	current->thread.vrsave = 0;
 	current->thread.used_vr = 0;
+	current->thread.load_vec = 0;
 #endif /* CONFIG_ALTIVEC */
 #ifdef CONFIG_SPE
 	memset(current->thread.evr, 0, sizeof(current->thread.evr));


Patches currently in stable-queue which might be from leitao@debian.org are

queue-4.9/powerpc-kernel-fix-fp-and-vector-register-restoration.patch
queue-4.9/powerpc-kernel-initialize-load_tm-on-task-creation.patch