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More arm64 fixes: 

- 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
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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"
This commit is contained in:
Linus Torvalds 2018-07-13 11:48:34 -07:00
parent e6ef760731 2fd8eb4ad8
commit 9d2e34897d
2 changed files with 11 additions and 14 deletions
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6
arch/arm64/Makefile
View File

@ -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

19
arch/arm64/include/asm/simd.h
View File

@ -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 */