Merge tag 'arm64-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux

Pull arm64 fixes from Will Deacon:
 "Catalin's out enjoying the sunshine, so I'm sending the fixes for a
  couple of weeks (although there hopefully won't be any more!).

  We've got a revert of a previous fix because it broke the build with
  some distro toolchains and a preemption fix when detemining whether or
  not the SIMD unit is in use.

  Summary:

   - Revert back to the 'linux' target for LD, as 'elf' breaks some
     distributions

   - Fix preemption race when testing whether the vector unit is in use
     or not"

* tag 'arm64-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux:
  arm64: neon: Fix function may_use_simd() return error status
  Revert "arm64: Use aarch64elf and aarch64elfb emulation mode variants"

arch/arm64/Makefile

@@ -60,13 +60,15 @@ ifeq ($(CONFIG_CPU_BIG_ENDIAN), y)
 KBUILD_CPPFLAGS	+= -mbig-endian
 CHECKFLAGS	+= -D__AARCH64EB__
 AS		+= -EB
-LDFLAGS		+= -EB -maarch64elfb
+# We must use the linux target here, since distributions don't tend to package
+# the ELF linker scripts with binutils, and this results in a build failure.
+LDFLAGS		+= -EB -maarch64linuxb
 UTS_MACHINE	:= aarch64_be
 else
 KBUILD_CPPFLAGS	+= -mlittle-endian
 CHECKFLAGS	+= -D__AARCH64EL__
 AS		+= -EL
-LDFLAGS		+= -EL -maarch64elf
+LDFLAGS		+= -EL -maarch64linux # See comment above
 UTS_MACHINE	:= aarch64
 endif
 

arch/arm64/include/asm/simd.h

@@ -29,20 +29,15 @@ DECLARE_PER_CPU(bool, kernel_neon_busy);
 static __must_check inline bool may_use_simd(void)
 {
 	/*
-	 * The raw_cpu_read() is racy if called with preemption enabled.
-	 * This is not a bug: kernel_neon_busy is only set when
-	 * preemption is disabled, so we cannot migrate to another CPU
-	 * while it is set, nor can we migrate to a CPU where it is set.
-	 * So, if we find it clear on some CPU then we're guaranteed to
-	 * find it clear on any CPU we could migrate to.
-	 *
-	 * If we are in between kernel_neon_begin()...kernel_neon_end(),
-	 * the flag will be set, but preemption is also disabled, so we
-	 * can't migrate to another CPU and spuriously see it become
-	 * false.
+	 * kernel_neon_busy is only set while preemption is disabled,
+	 * and is clear whenever preemption is enabled. Since
+	 * this_cpu_read() is atomic w.r.t. preemption, kernel_neon_busy
+	 * cannot change under our feet -- if it's set we cannot be
+	 * migrated, and if it's clear we cannot be migrated to a CPU
+	 * where it is set.
 	 */
 	return !in_irq() && !irqs_disabled() && !in_nmi() &&
-		!raw_cpu_read(kernel_neon_busy);
+		!this_cpu_read(kernel_neon_busy);
 }
 
 #else /* ! CONFIG_KERNEL_MODE_NEON */