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x86/cpu: Use SERIALIZE in sync_core() when available

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The SERIALIZE instruction gives software a way to force the processor to
complete all modifications to flags, registers and memory from previous
instructions and drain all buffered writes to memory before the next
instruction is fetched and executed. Thus, it serves the purpose of
sync_core(). Use it when available.

Suggested-by: Andy Lutomirski <luto@kernel.org>
Signed-off-by: Ricardo Neri <ricardo.neri-calderon@linux.intel.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Reviewed-by: Tony Luck <tony.luck@intel.com>
Link: https://lkml.kernel.org/r/20200807032833.17484-1-ricardo.neri-calderon@linux.intel.com
This commit is contained in:
Ricardo Neri 2020-08-06 20:28:33 -07:00 committed by Borislav Petkov
parent 9123e3a74e
commit bf9c912f9a
2 changed files with 24 additions and 8 deletions
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6
arch/x86/include/asm/special_insns.h
View file

@ -234,6 +234,12 @@ static inline void clwb(volatile void *__p)
#define nop() asm volatile ("nop")
static inline void serialize(void)
{
/* Instruction opcode for SERIALIZE; supported in binutils >= 2.35. */
asm volatile(".byte 0xf, 0x1, 0xe8" ::: "memory");
}
#endif /* __KERNEL__ */
#endif /* _ASM_X86_SPECIAL_INSNS_H */

26
arch/x86/include/asm/sync_core.h
View file

@ -5,6 +5,7 @@
#include <linux/preempt.h>
#include <asm/processor.h>
#include <asm/cpufeature.h>
#include <asm/special_insns.h>
#ifdef CONFIG_X86_32
static inline void iret_to_self(void)
@ -54,14 +55,23 @@ static inline void iret_to_self(void)
static inline void sync_core(void)
{
/*
* There are quite a few ways to do this. IRET-to-self is nice
* because it works on every CPU, at any CPL (so it's compatible
* with paravirtualization), and it never exits to a hypervisor.
* The only down sides are that it's a bit slow (it seems to be
* a bit more than 2x slower than the fastest options) and that
* it unmasks NMIs. The "push %cs" is needed because, in
* paravirtual environments, __KERNEL_CS may not be a valid CS
* value when we do IRET directly.
* The SERIALIZE instruction is the most straightforward way to
* do this but it not universally available.
*/
if (static_cpu_has(X86_FEATURE_SERIALIZE)) {
serialize();
return;
}
/*
* For all other processors, there are quite a few ways to do this.
* IRET-to-self is nice because it works on every CPU, at any CPL
* (so it's compatible with paravirtualization), and it never exits
* to a hypervisor. The only down sides are that it's a bit slow
* (it seems to be a bit more than 2x slower than the fastest
* options) and that it unmasks NMIs. The "push %cs" is needed
* because, in paravirtual environments, __KERNEL_CS may not be a
* valid CS value when we do IRET directly.
*
* In case NMI unmasking or performance ever becomes a problem,
* the next best option appears to be MOV-to-CR2 and an