linux-kernel - [PATCH] drm/i915: check to see if SIMD registers are available before using SIMD

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Message-Id: <20200430221016.3866-1-Jason@zx2c4.com>
Date:   Thu, 30 Apr 2020 16:10:16 -0600
From:   "Jason A. Donenfeld" <Jason@...c4.com>
To:     linux-kernel@...r.kernel.org, intel-gfx@...ts.freedesktop.org,
        dri-devel@...ts.freedesktop.org, bigeasy@...utronix.de,
        tglx@...utronix.de, chris@...is-wilson.co.uk
Cc:     "Jason A. Donenfeld" <Jason@...c4.com>, stable@...r.kernel.org
Subject: [PATCH] drm/i915: check to see if SIMD registers are available before using SIMD

Sometimes it's not okay to use SIMD registers, the conditions for which
have changed subtly from kernel release to kernel release. Usually the
pattern is to check for may_use_simd() and then fallback to using
something slower in the unlikely case SIMD registers aren't available.
So, this patch fixes up i915's accelerated memcpy routines to fallback
to boring memcpy if may_use_simd() is false.

Cc: stable@...r.kernel.org
Signed-off-by: Jason A. Donenfeld <Jason@...c4.com>
---
 drivers/gpu/drm/i915/i915_memcpy.c | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/drivers/gpu/drm/i915/i915_memcpy.c b/drivers/gpu/drm/i915/i915_memcpy.c
index fdd550405fd3..7c0e022586bc 100644
--- a/drivers/gpu/drm/i915/i915_memcpy.c
+++ b/drivers/gpu/drm/i915/i915_memcpy.c
@@ -24,6 +24,7 @@
 
 #include <linux/kernel.h>
 #include <asm/fpu/api.h>
+#include <asm/simd.h>
 
 #include "i915_memcpy.h"
 
@@ -38,6 +39,12 @@ static DEFINE_STATIC_KEY_FALSE(has_movntdqa);
 #ifdef CONFIG_AS_MOVNTDQA
 static void __memcpy_ntdqa(void *dst, const void *src, unsigned long len)
 {
+	if (unlikely(!may_use_simd())) {
+		memcpy(dst, src, len);
+		return;
+	}
+
+
 	kernel_fpu_begin();
 
 	while (len >= 4) {
@@ -67,6 +74,11 @@ static void __memcpy_ntdqa(void *dst, const void *src, unsigned long len)
 
 static void __memcpy_ntdqu(void *dst, const void *src, unsigned long len)
 {
+	if (unlikely(!may_use_simd())) {
+		memcpy(dst, src, len);
+		return;
+	}
+
 	kernel_fpu_begin();
 
 	while (len >= 4) {
-- 
2.26.2