From 74f0c301f5493f4dcae08f3b723432d7b79ac7c0 Mon Sep 17 00:00:00 2001
From: Dave Martin <Dave.Martin@arm.com>
Date: Thu, 30 Nov 2017 11:56:37 +0000
Subject: [PATCH] arm64: fpsimd: Fix failure to restore FPSIMD state after
 signals
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Git-commit: 9de52a755cfb6da5ee21a07e3a868bdc8fbfccb3
Patch-mainline: v4.15-rc2
References: fate#325866

The fpsimd_update_current_state() function is responsible for
loading the FPSIMD state from the user signal frame into the
current task during sigreturn.  When implementing support for SVE,
conditional code was added to this function in order to handle the
case where SVE state need to be loaded for the task and merged with
the FPSIMD data from the signal frame; however, the FPSIMD-only
case was unintentionally dropped.

As a result of this, sigreturn does not currently restore the
FPSIMD state of the task, except in the case where the system
supports SVE and the signal frame contains SVE state in addition to
FPSIMD state.

This patch fixes this bug by making the copy-in of the FPSIMD data
from the signal frame to thread_struct unconditional.

This remains a performance regression from v4.14, since the FPSIMD
state is now copied into thread_struct and then loaded back,
instead of _only_ being loaded into the CPU FPSIMD registers.
However, it is essential to call task_fpsimd_load() here anyway in
order to ensure that the SVE enable bit in CPACR_EL1 is set
correctly before returning to userspace.  This could use some
refactoring, but since sigreturn is not a fast path I have kept
this patch as a pure fix and left the refactoring for later.

Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Fixes: 8cd969d28fd2 ("arm64/sve: Signal handling support")
Reported-by: Alex Bennée <alex.bennee@linaro.org>
Tested-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Signed-off-by: Dave Martin <Dave.Martin@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Mian Yousaf Kaukab <yousaf.kaukab@suse.com>
---
 arch/arm64/kernel/fpsimd.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/arch/arm64/kernel/fpsimd.c b/arch/arm64/kernel/fpsimd.c
index 8b1a31f526ea..e8f2529c264a 100644
--- a/arch/arm64/kernel/fpsimd.c
+++ b/arch/arm64/kernel/fpsimd.c
@@ -1026,10 +1026,10 @@ void fpsimd_update_current_state(struct fpsimd_state *state)
 
 	local_bh_disable();
 
-	if (system_supports_sve() && test_thread_flag(TIF_SVE)) {
-		current->thread.fpsimd_state = *state;
+	current->thread.fpsimd_state = *state;
+	if (system_supports_sve() && test_thread_flag(TIF_SVE))
 		fpsimd_to_sve(current);
-	}
+
 	task_fpsimd_load();
 
 	if (test_and_clear_thread_flag(TIF_FOREIGN_FPSTATE)) {
-- 
2.11.0