There are a number of situations where the mandatory barriers rmb() and
wmb() are used to order memory/memory operations in the device drivers
and those barriers are much heavier than they actually need to be. For
example in the case of PowerPC wmb() calls the heavy-weight sync
instruction when for coherent memory operations all that is really needed
is an lsync or eieio instruction.
This commit adds a coherent only version of the mandatory memory barriers
rmb() and wmb(). In most cases this should result in the barrier being the
same as the SMP barriers for the SMP case, however in some cases we use a
barrier that is somewhere in between rmb() and smp_rmb(). For example on
ARM the rmb barriers break down as follows:
Barrier Call Explanation
--------- -------- ----------------------------------
rmb() dsb() Data synchronization barrier - system
dma_rmb() dmb(osh) data memory barrier - outer sharable
smp_rmb() dmb(ish) data memory barrier - inner sharable
These new barriers are not as safe as the standard rmb() and wmb().
Specifically they do not guarantee ordering between coherent and incoherent
memories. The primary use case for these would be to enforce ordering of
reads and writes when accessing coherent memory that is shared between the
CPU and a device.
It may also be noted that there is no dma_mb(). Most architectures don't
provide a good mechanism for performing a coherent only full barrier without
resorting to the same mechanism used in mb(). As such there isn't much to
be gained in trying to define such a function.
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
Cc: Michael Ellerman <michael@ellerman.id.au>
Cc: Michael Neuling <mikey@neuling.org>
Cc: Russell King <linux@arm.linux.org.uk>
Cc: Geert Uytterhoeven <geert@linux-m68k.org>
Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
Cc: Tony Luck <tony.luck@intel.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: David Miller <davem@davemloft.net>
Acked-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Acked-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Alexander Duyck <alexander.h.duyck@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Strings library contributed to glibc but re-licensed under GPLv2)
- Optimised crypto algorithms making use of the ARMv8 crypto extensions
(together with kernel API for using FPSIMD instructions in interrupt
context)
- Ftrace support
- CPU topology parsing from DT
- ESR_EL1 (Exception Syndrome Register) exposed to user space signal
handlers for SIGSEGV/SIGBUS (useful to emulation tools like Qemu)
- 1GB section linear mapping if applicable
- Barriers usage clean-up
- Default pgprot clean-up
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Merge tag 'arm64-upstream' of git://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux into next
Pull arm64 updates from Catalin Marinas:
- Optimised assembly string/memory routines (based on the AArch64
Cortex Strings library contributed to glibc but re-licensed under
GPLv2)
- Optimised crypto algorithms making use of the ARMv8 crypto extensions
(together with kernel API for using FPSIMD instructions in interrupt
context)
- Ftrace support
- CPU topology parsing from DT
- ESR_EL1 (Exception Syndrome Register) exposed to user space signal
handlers for SIGSEGV/SIGBUS (useful to emulation tools like Qemu)
- 1GB section linear mapping if applicable
- Barriers usage clean-up
- Default pgprot clean-up
Conflicts as per Catalin.
* tag 'arm64-upstream' of git://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux: (57 commits)
arm64: kernel: initialize broadcast hrtimer based clock event device
arm64: ftrace: Add system call tracepoint
arm64: ftrace: Add CALLER_ADDRx macros
arm64: ftrace: Add dynamic ftrace support
arm64: Add ftrace support
ftrace: Add arm64 support to recordmcount
arm64: Add 'notrace' attribute to unwind_frame() for ftrace
arm64: add __ASSEMBLY__ in asm/insn.h
arm64: Fix linker script entry point
arm64: lib: Implement optimized string length routines
arm64: lib: Implement optimized string compare routines
arm64: lib: Implement optimized memcmp routine
arm64: lib: Implement optimized memset routine
arm64: lib: Implement optimized memmove routine
arm64: lib: Implement optimized memcpy routine
arm64: defconfig: enable a few more common/useful options in defconfig
ftrace: Make CALLER_ADDRx macros more generic
arm64: Fix deadlock scenario with smp_send_stop()
arm64: Fix machine_shutdown() definition
arm64: Support arch_irq_work_raise() via self IPIs
...
The recently introduced acquire/release accessors refer to smp_mb()
in the !CONFIG_SMP case. This is confusing when reading the code, so use
barrier() directly when we know we're UP.
Acked-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Now that all callers of the barrier macros are updated to pass the
mandatory options, update the macros so the option is actually used.
Acked-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
When calling our low-level barrier macros directly, we can often suffice
with more relaxed behaviour than the default "all accesses, full system"
option.
This patch updates the users of dsb() to specify the option which they
actually require.
Acked-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
AARGH64 uses ll/sc primitives that do not imply any barriers for the
normal atomics, therefore smp_mb__{before,after} should be a full
barrier.
Since AARGH64 doesn't use asm-generic/barrier.h, add the required
definitions to its asm/barrier.h.
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Acked-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Link: http://lkml.kernel.org/n/tip-8p5iclqgy78al33kck3ht7nr@git.kernel.org
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Chen Gang <gang.chen@asianux.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Russell King <rmk+kernel@arm.linux.org.uk>
Cc: Will Deacon <will.deacon@arm.com>
Cc: linux-arm-kernel@lists.infradead.org
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Commit 8adbf57fc4 ("irqchip: gic: use dmb ishst instead of dsb when
raising a softirq") added an explicit dmb(...) call to the GIC driver.
This patch adds a simple dmb() macro to arm64, which expands to a DMB SY
instruction.
Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
The dsb instruction takes an option specifying both the target access
types and shareability domain.
This patch allows such an option to be passed to the dsb macro,
resulting in potentially more efficient code. Currently the option is
ignored until all callers are updated (unlike ARM, the option is
mandated by the assembler).
Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
A number of situations currently require the heavyweight smp_mb(),
even though there is no need to order prior stores against later
loads. Many architectures have much cheaper ways to handle these
situations, but the Linux kernel currently has no portable way
to make use of them.
This commit therefore supplies smp_load_acquire() and
smp_store_release() to remedy this situation. The new
smp_load_acquire() primitive orders the specified load against
any subsequent reads or writes, while the new smp_store_release()
primitive orders the specifed store against any prior reads or
writes. These primitives allow array-based circular FIFOs to be
implemented without an smp_mb(), and also allow a theoretical
hole in rcu_assign_pointer() to be closed at no additional
expense on most architectures.
In addition, the RCU experience transitioning from explicit
smp_read_barrier_depends() and smp_wmb() to rcu_dereference()
and rcu_assign_pointer(), respectively resulted in substantial
improvements in readability. It therefore seems likely that
replacing other explicit barriers with smp_load_acquire() and
smp_store_release() will provide similar benefits. It appears
that roughly half of the explicit barriers in core kernel code
might be so replaced.
[Changelog by PaulMck]
Reviewed-by: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Acked-by: Will Deacon <will.deacon@arm.com>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
Cc: Michael Ellerman <michael@ellerman.id.au>
Cc: Michael Neuling <mikey@neuling.org>
Cc: Russell King <linux@arm.linux.org.uk>
Cc: Geert Uytterhoeven <geert@linux-m68k.org>
Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
Cc: Victor Kaplansky <VICTORK@il.ibm.com>
Cc: Tony Luck <tony.luck@intel.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Link: http://lkml.kernel.org/r/20131213150640.908486364@infradead.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
This patch introduces a few AArch64-specific header files together with
Kbuild entries for generic headers.
Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Acked-by: Tony Lindgren <tony@atomide.com>
Acked-by: Nicolas Pitre <nico@linaro.org>
Acked-by: Olof Johansson <olof@lixom.net>
Acked-by: Santosh Shilimkar <santosh.shilimkar@ti.com>
Acked-by: Arnd Bergmann <arnd@arndb.de>
