Add support for the new CLWB (cache line write back)
instruction. This instruction was announced in the document
"Intel Architecture Instruction Set Extensions Programming
Reference" with reference number 319433-022.
https://software.intel.com/sites/default/files/managed/0d/53/319433-022.pdf
The CLWB instruction is used to write back the contents of
dirtied cache lines to memory without evicting the cache lines
from the processor's cache hierarchy. This should be used in
favor of clflushopt or clflush in cases where you require the
cache line to be written to memory but plan to access the data
again in the near future.
One of the main use cases for this is with persistent memory
where CLWB can be used with PCOMMIT to ensure that data has been
accepted to memory and is durable on the DIMM.
This function shows how to properly use CLWB/CLFLUSHOPT/CLFLUSH
and PCOMMIT with appropriate fencing:
void flush_and_commit_buffer(void *vaddr, unsigned int size)
{
void *vend = vaddr + size - 1;
for (; vaddr < vend; vaddr += boot_cpu_data.x86_clflush_size)
clwb(vaddr);
/* Flush any possible final partial cacheline */
clwb(vend);
/*
* Use SFENCE to order CLWB/CLFLUSHOPT/CLFLUSH cache flushes.
* (MFENCE via mb() also works)
*/
wmb();
/* PCOMMIT and the required SFENCE for ordering */
pcommit_sfence();
}
After this function completes the data pointed to by vaddr is
has been accepted to memory and will be durable if the vaddr
points to persistent memory.
Regarding the details of how the alternatives assembly is set
up, we need one additional byte at the beginning of the CLFLUSH
so that we can flip it into a CLFLUSHOPT by changing that byte
into a 0x66 prefix. Two options are to either insert a 1 byte
ASM_NOP1, or to add a 1 byte NOP_DS_PREFIX. Both have no
functional effect with the plain CLFLUSH, but I've been told
that executing a CLFLUSH + prefix should be faster than
executing a CLFLUSH + NOP.
We had to hard code the assembly for CLWB because, lacking the
ability to assemble the CLWB instruction itself, the next
closest thing is to have an xsaveopt instruction with a 0x66
prefix. Unfortunately XSAVEOPT itself is also relatively new,
and isn't included by all the GCC versions that the kernel needs
to support.
Signed-off-by: Ross Zwisler <ross.zwisler@linux.intel.com>
Acked-by: Borislav Petkov <bp@suse.de>
Acked-by: H. Peter Anvin <hpa@linux.intel.com>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/1422377631-8986-3-git-send-email-ross.zwisler@linux.intel.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Add support for the new pcommit (persistent commit) instruction.
This instruction was announced in the document "Intel
Architecture Instruction Set Extensions Programming Reference"
with reference number 319433-022:
https://software.intel.com/sites/default/files/managed/0d/53/319433-022.pdf
The pcommit instruction ensures that data that has been flushed
from the processor's cache hierarchy with clwb, clflushopt or
clflush is accepted to memory and is durable on the DIMM. The
primary use case for this is persistent memory.
This function shows how to properly use clwb/clflushopt/clflush
and pcommit with appropriate fencing:
void flush_and_commit_buffer(void *vaddr, unsigned int size)
{
void *vend = vaddr + size - 1;
for (; vaddr < vend; vaddr += boot_cpu_data.x86_clflush_size)
clwb(vaddr);
/* Flush any possible final partial cacheline */
clwb(vend);
/*
* sfence to order clwb/clflushopt/clflush cache flushes
* mfence via mb() also works
*/
wmb();
/* pcommit and the required sfence for ordering */
pcommit_sfence();
}
After this function completes the data pointed to by vaddr is
has been accepted to memory and will be durable if the vaddr
points to persistent memory.
Pcommit must always be ordered by an mfence or sfence, so to
help simplify things we include both the pcommit and the
required sfence in the alternatives generated by
pcommit_sfence(). The other option is to keep them separated,
but on platforms that don't support pcommit this would then turn
into:
void flush_and_commit_buffer(void *vaddr, unsigned int size)
{
void *vend = vaddr + size - 1;
for (; vaddr < vend; vaddr += boot_cpu_data.x86_clflush_size)
clwb(vaddr);
/* Flush any possible final partial cacheline */
clwb(vend);
/*
* sfence to order clwb/clflushopt/clflush cache flushes
* mfence via mb() also works
*/
wmb();
nop(); /* from pcommit(), via alternatives */
/*
* sfence to order pcommit
* mfence via mb() also works
*/
wmb();
}
This is still correct, but now you've got two fences separated
by only a nop. With the commit and the fence together in
pcommit_sfence() you avoid the final unneeded fence.
Signed-off-by: Ross Zwisler <ross.zwisler@linux.intel.com>
Acked-by: Borislav Petkov <bp@suse.de>
Acked-by: H. Peter Anvin <hpa@linux.intel.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/1424367448-24254-1-git-send-email-ross.zwisler@linux.intel.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Context switches and TLB flushes can change individual bits of CR4.
CR4 reads take several cycles, so store a shadow copy of CR4 in a
per-cpu variable.
To avoid wasting a cache line, I added the CR4 shadow to
cpu_tlbstate, which is already touched in switch_mm. The heaviest
users of the cr4 shadow will be switch_mm and __switch_to_xtra, and
__switch_to_xtra is called shortly after switch_mm during context
switch, so the cacheline is likely to be hot.
Signed-off-by: Andy Lutomirski <luto@amacapital.net>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Kees Cook <keescook@chromium.org>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Vince Weaver <vince@deater.net>
Cc: "hillf.zj" <hillf.zj@alibaba-inc.com>
Cc: Valdis Kletnieks <Valdis.Kletnieks@vt.edu>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Arnaldo Carvalho de Melo <acme@kernel.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: http://lkml.kernel.org/r/3a54dd3353fffbf84804398e00dfdc5b7c1afd7d.1414190806.git.luto@amacapital.net
Signed-off-by: Ingo Molnar <mingo@kernel.org>
It being static causes over a dozen instances to be scattered
across the kernel image, with non of them ever being referenced
in any way. Making the variable extern without ever defining it
works as well - all we need is to have the compiler think the
variable is being accessed.
Signed-off-by: Jan Beulich <jbeulich@suse.com>
Link: http://lkml.kernel.org/r/51A610B802000078000D99A0@nat28.tlf.novell.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
