RDPID is a new instruction that reads MSR_TSC_AUX quickly. This should be considerably faster than reading the GDT. Add a cpufeature for it and use it from __vdso_getcpu when available.
Signed-off-by: Andy Lutomirski <[email protected]> --- I don't have a Cannonlake CPU (or whatever CPU I'd need for this). Could someone who has such a beast give this a try? Boris, could you double-check me? You're a lot more familiar with CPUID stuff and the instruction tables than I am, and I can't fall back to a real disassembler because the instruction is too new. Also, it's time for someone to do UMIP. I'll see if I can convince someone in KVM land to emulate it to make it easier to test. arch/x86/include/asm/cpufeatures.h | 1 + arch/x86/include/asm/special_insns.h | 8 ++++++++ arch/x86/include/asm/vgtod.h | 7 ++++++- 3 files changed, 15 insertions(+), 1 deletion(-) diff --git a/arch/x86/include/asm/cpufeatures.h b/arch/x86/include/asm/cpufeatures.h index 7bfb6b70c745..beaf2fb601ee 100644 --- a/arch/x86/include/asm/cpufeatures.h +++ b/arch/x86/include/asm/cpufeatures.h @@ -279,6 +279,7 @@ /* Intel-defined CPU features, CPUID level 0x00000007:0 (ecx), word 16 */ #define X86_FEATURE_PKU (16*32+ 3) /* Protection Keys for Userspace */ #define X86_FEATURE_OSPKE (16*32+ 4) /* OS Protection Keys Enable */ +#define X86_FEATURE_RDPID (16*32+ 22) /* RDPID instruction */ /* * BUG word(s) diff --git a/arch/x86/include/asm/special_insns.h b/arch/x86/include/asm/special_insns.h index d96d04377765..de64c404dc74 100644 --- a/arch/x86/include/asm/special_insns.h +++ b/arch/x86/include/asm/special_insns.h @@ -301,6 +301,14 @@ static inline void pcommit_sfence(void) #define nop() asm volatile ("nop") +/* Read MSR_TSC_AUX using RDPID. */ +static inline unsigned int rdpid(void) +{ + unsigned int pid; + + asm (".byte 0xf3,0x0f,0xc7,0xf8" : "=a" (pid)); /* RDPID %eax/rax */ + return pid; +} #endif /* __KERNEL__ */ diff --git a/arch/x86/include/asm/vgtod.h b/arch/x86/include/asm/vgtod.h index e728699db774..3a01996db58f 100644 --- a/arch/x86/include/asm/vgtod.h +++ b/arch/x86/include/asm/vgtod.h @@ -89,8 +89,13 @@ static inline unsigned int __getcpu(void) * works on all CPUs. This is volatile so that it orders * correctly wrt barrier() and to keep gcc from cleverly * hoisting it out of the calling function. + * + * If RDPID is available, use it. */ - asm volatile ("lsl %1,%0" : "=r" (p) : "r" (__PER_CPU_SEG)); + alternative_io ("lsl %[p],%[seg]", + ".byte 0xf3,0x0f,0xc7,0xf8", /* RDPID %eax/rax */ + X86_FEATURE_RDPID, + [p] "=a" (p), [seg] "r" (__PER_CPU_SEG)); return p; } -- 2.5.5
