MFC 310048,310101,310239

310048
    hyperv: Implement "enlightened" time counter, which is rdtsc based.

    Reviewed by:    kib
    Sponsored by:   Microsoft
    Differential Revision:  https://reviews.freebsd.org/D8763

310101
    hyperv: Allow userland to ro-mmap reference TSC page

    This paves way to implement VDSO for the enlightened time counter.

    Reviewed by:    kib
    Sponsored by:   Microsoft
    Differential Revision:  https://reviews.freebsd.org/D8768

310239
    hyperv: Implement userspace gettimeofday(2) with Hyper-V reference TSC

    This 6 times gettimeofday performance, as measured by
    tools/tools/syscall_timing

    Reviewed by:    kib
    Sponsored by:   Microsoft
    Differential Revision:  https://reviews.freebsd.org/D8789

1 files changed, 73 insertions, 0 deletions

diff --git a/lib/libc/x86/sys/__vdso_gettc.c b/lib/libc/x86/sys/__vdso_gettc.c
index 743b3ad..5097ad5 100644
--- a/lib/libc/x86/sys/__vdso_gettc.c
+++ b/lib/libc/x86/sys/__vdso_gettc.c
@@ -45,6 +45,10 @@ __FBSDID("$FreeBSD$");
 #include <machine/cpufunc.h>
 #include <machine/specialreg.h>
 #include <dev/acpica/acpi_hpet.h>
+#ifdef __amd64__
+#include <machine/atomic.h>
+#include <dev/hyperv/hyperv.h>
+#endif
 #include "libc_private.h"
 
 static void
@@ -144,6 +148,67 @@ __vdso_init_hpet(uint32_t u)
 	_close(fd);
 }
 
+#ifdef __amd64__
+
+#define HYPERV_REFTSC_DEVPATH	"/dev/" HYPERV_REFTSC_DEVNAME
+
+/*
+ * NOTE:
+ * We use 'NULL' for this variable to indicate that initialization
+ * is required.  And if this variable is 'MAP_FAILED', then Hyper-V
+ * reference TSC can not be used, e.g. in misconfigured jail.
+ */
+static struct hyperv_reftsc *hyperv_ref_tsc;
+
+static void
+__vdso_init_hyperv_tsc(void)
+{
+	int fd;
+
+	fd = _open(HYPERV_REFTSC_DEVPATH, O_RDONLY);
+	if (fd < 0) {
+		/* Prevent the caller from re-entering. */
+		hyperv_ref_tsc = MAP_FAILED;
+		return;
+	}
+	hyperv_ref_tsc = mmap(NULL, sizeof(*hyperv_ref_tsc), PROT_READ,
+	    MAP_SHARED, fd, 0);
+	_close(fd);
+}
+
+static int
+__vdso_hyperv_tsc(struct hyperv_reftsc *tsc_ref, u_int *tc)
+{
+	uint64_t disc, ret, tsc, scale;
+	uint32_t seq;
+	int64_t ofs;
+
+	while ((seq = atomic_load_acq_int(&tsc_ref->tsc_seq)) != 0) {
+		scale = tsc_ref->tsc_scale;
+		ofs = tsc_ref->tsc_ofs;
+
+		lfence_mb();
+		tsc = rdtsc();
+
+		/* ret = ((tsc * scale) >> 64) + ofs */
+		__asm__ __volatile__ ("mulq %3" :
+		    "=d" (ret), "=a" (disc) :
+		    "a" (tsc), "r" (scale));
+		ret += ofs;
+
+		atomic_thread_fence_acq();
+		if (tsc_ref->tsc_seq == seq) {
+			*tc = ret;
+			return (0);
+		}
+
+		/* Sequence changed; re-sync. */
+	}
+	return (ENOSYS);
+}
+
+#endif	/* __amd64__ */
+
 #pragma weak __vdso_gettc
 int
 __vdso_gettc(const struct vdso_timehands *th, u_int *tc)
@@ -165,6 +230,14 @@ __vdso_gettc(const struct vdso_timehands *th, u_int *tc)
 			return (ENOSYS);
 		*tc = *(volatile uint32_t *)(hpet_dev_map + HPET_MAIN_COUNTER);
 		return (0);
+#ifdef __amd64__
+	case VDSO_TH_ALGO_X86_HVTSC:
+		if (hyperv_ref_tsc == NULL)
+			__vdso_init_hyperv_tsc();
+		if (hyperv_ref_tsc == MAP_FAILED)
+			return (ENOSYS);
+		return (__vdso_hyperv_tsc(hyperv_ref_tsc, tc));
+#endif
 	default:
 		return (ENOSYS);
 	}