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commit 6ea98b4baa1c9089d7a035ebccb993e03d1ac57f
parent 45802da05e666a81b421422d3e302930c0e24e77
Author: Linus Torvalds <torvalds@linux-foundation.org>
Date:   Wed,  6 Mar 2019 08:45:46 -0800

Merge branch 'x86-alternatives-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull x86 alternative instruction updates from Ingo Molnar:
 "Small RDTSCP opimization, enabled by the newly added ALTERNATIVE_3(),
  and other small improvements"

* 'x86-alternatives-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  x86/TSC: Use RDTSCP
  x86/alternatives: Add an ALTERNATIVE_3() macro
  x86/alternatives: Print containing function
  x86/alternatives: Add macro comments

Diffstat:
March/x86/include/asm/alternative.h | 39++++++++++++++++++++++++++++++++-------
March/x86/include/asm/msr.h | 16++++++++++++++--
March/x86/kernel/alternative.c | 4++--
3 files changed, 48 insertions(+), 11 deletions(-)

diff --git a/arch/x86/include/asm/alternative.h b/arch/x86/include/asm/alternative.h @@ -94,13 +94,12 @@ static inline int alternatives_text_reserved(void *start, void *end) #define alt_total_slen alt_end_marker"b-661b" #define alt_rlen(num) e_replacement(num)"f-"b_replacement(num)"f" -#define __OLDINSTR(oldinstr, num) \ +#define OLDINSTR(oldinstr, num) \ + "# ALT: oldnstr\n" \ "661:\n\t" oldinstr "\n662:\n" \ + "# ALT: padding\n" \ ".skip -(((" alt_rlen(num) ")-(" alt_slen ")) > 0) * " \ - "((" alt_rlen(num) ")-(" alt_slen ")),0x90\n" - -#define OLDINSTR(oldinstr, num) \ - __OLDINSTR(oldinstr, num) \ + "((" alt_rlen(num) ")-(" alt_slen ")),0x90\n" \ alt_end_marker ":\n" /* @@ -116,11 +115,23 @@ static inline int alternatives_text_reserved(void *start, void *end) * additionally longer than the first replacement alternative. */ #define OLDINSTR_2(oldinstr, num1, num2) \ + "# ALT: oldinstr2\n" \ "661:\n\t" oldinstr "\n662:\n" \ + "# ALT: padding2\n" \ ".skip -((" alt_max_short(alt_rlen(num1), alt_rlen(num2)) " - (" alt_slen ")) > 0) * " \ "(" alt_max_short(alt_rlen(num1), alt_rlen(num2)) " - (" alt_slen ")), 0x90\n" \ alt_end_marker ":\n" +#define OLDINSTR_3(oldinsn, n1, n2, n3) \ + "# ALT: oldinstr3\n" \ + "661:\n\t" oldinsn "\n662:\n" \ + "# ALT: padding3\n" \ + ".skip -((" alt_max_short(alt_max_short(alt_rlen(n1), alt_rlen(n2)), alt_rlen(n3)) \ + " - (" alt_slen ")) > 0) * " \ + "(" alt_max_short(alt_max_short(alt_rlen(n1), alt_rlen(n2)), alt_rlen(n3)) \ + " - (" alt_slen ")), 0x90\n" \ + alt_end_marker ":\n" + #define ALTINSTR_ENTRY(feature, num) \ " .long 661b - .\n" /* label */ \ " .long " b_replacement(num)"f - .\n" /* new instruction */ \ @@ -129,8 +140,9 @@ static inline int alternatives_text_reserved(void *start, void *end) " .byte " alt_rlen(num) "\n" /* replacement len */ \ " .byte " alt_pad_len "\n" /* pad len */ -#define ALTINSTR_REPLACEMENT(newinstr, feature, num) /* replacement */ \ - b_replacement(num)":\n\t" newinstr "\n" e_replacement(num) ":\n\t" +#define ALTINSTR_REPLACEMENT(newinstr, feature, num) /* replacement */ \ + "# ALT: replacement " #num "\n" \ + b_replacement(num)":\n\t" newinstr "\n" e_replacement(num) ":\n" /* alternative assembly primitive: */ #define ALTERNATIVE(oldinstr, newinstr, feature) \ @@ -153,6 +165,19 @@ static inline int alternatives_text_reserved(void *start, void *end) ALTINSTR_REPLACEMENT(newinstr2, feature2, 2) \ ".popsection\n" +#define ALTERNATIVE_3(oldinsn, newinsn1, feat1, newinsn2, feat2, newinsn3, feat3) \ + OLDINSTR_3(oldinsn, 1, 2, 3) \ + ".pushsection .altinstructions,\"a\"\n" \ + ALTINSTR_ENTRY(feat1, 1) \ + ALTINSTR_ENTRY(feat2, 2) \ + ALTINSTR_ENTRY(feat3, 3) \ + ".popsection\n" \ + ".pushsection .altinstr_replacement, \"ax\"\n" \ + ALTINSTR_REPLACEMENT(newinsn1, feat1, 1) \ + ALTINSTR_REPLACEMENT(newinsn2, feat2, 2) \ + ALTINSTR_REPLACEMENT(newinsn3, feat3, 3) \ + ".popsection\n" + /* * Alternative instructions for different CPU types or capabilities. * diff --git a/arch/x86/include/asm/msr.h b/arch/x86/include/asm/msr.h @@ -217,6 +217,8 @@ static __always_inline unsigned long long rdtsc(void) */ static __always_inline unsigned long long rdtsc_ordered(void) { + DECLARE_ARGS(val, low, high); + /* * The RDTSC instruction is not ordered relative to memory * access. The Intel SDM and the AMD APM are both vague on this @@ -227,9 +229,19 @@ static __always_inline unsigned long long rdtsc_ordered(void) * ordering guarantees as reading from a global memory location * that some other imaginary CPU is updating continuously with a * time stamp. + * + * Thus, use the preferred barrier on the respective CPU, aiming for + * RDTSCP as the default. */ - barrier_nospec(); - return rdtsc(); + asm volatile(ALTERNATIVE_3("rdtsc", + "mfence; rdtsc", X86_FEATURE_MFENCE_RDTSC, + "lfence; rdtsc", X86_FEATURE_LFENCE_RDTSC, + "rdtscp", X86_FEATURE_RDTSCP) + : EAX_EDX_RET(val, low, high) + /* RDTSCP clobbers ECX with MSR_TSC_AUX. */ + :: "ecx"); + + return EAX_EDX_VAL(val, low, high); } static inline unsigned long long native_read_pmc(int counter) diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c @@ -394,10 +394,10 @@ void __init_or_module noinline apply_alternatives(struct alt_instr *start, continue; } - DPRINTK("feat: %d*32+%d, old: (%px len: %d), repl: (%px, len: %d), pad: %d", + DPRINTK("feat: %d*32+%d, old: (%pS (%px) len: %d), repl: (%px, len: %d), pad: %d", a->cpuid >> 5, a->cpuid & 0x1f, - instr, a->instrlen, + instr, instr, a->instrlen, replacement, a->replacementlen, a->padlen); DUMP_BYTES(instr, a->instrlen, "%px: old_insn: ", instr);