[PATCH 1/4] Add helper functions for paravirtual clocksources.

Gerd Hoffmann
2008-04-24T08:37:05Z

Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
---
arch/x86/Kconfig | 4 +
arch/x86/kernel/Makefile | 1 +
arch/x86/kernel/pvclock.c | 146 +++++++++++++++++++++++++++++++++++++++++++++
include/asm-x86/pvclock.h | 6 ++
4 files changed, 157 insertions(+), 0 deletions(-)
create mode 100644 arch/x86/kernel/pvclock.c
create mode 100644 include/asm-x86/pvclock.h

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index a22be4a..fe73d38 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -400,6 +400,10 @@ config PARAVIRT
over full virtualization. However, when run without a hypervisor
the kernel is theoretically slower and slightly larger.

+config PARAVIRT_CLOCK
+ bool
+ default n
+
endif

config MEMTEST_BOOTPARAM
diff --git a/arch/x86/kernel/Makefile b/arch/x86/kernel/Makefile
index fa19c38..ab7999c 100644
--- a/arch/x86/kernel/Makefile
+++ b/arch/x86/kernel/Makefile
@@ -83,6 +83,7 @@ obj-$(CONFIG_VMI) += vmi_32.o vmiclock_32.o
obj-$(CONFIG_KVM_GUEST) += kvm.o
obj-$(CONFIG_KVM_CLOCK) += kvmclock.o
obj-$(CONFIG_PARAVIRT) += paravirt.o paravirt_patch_$(BITS).o
+obj-$(CONFIG_PARAVIRT_CLOCK) += pvclock.o

ifdef CONFIG_INPUT_PCSPKR
obj-y += pcspeaker.o
diff --git a/arch/x86/kernel/pvclock.c b/arch/x86/kernel/pvclock.c
new file mode 100644
index 0000000..fecf17a
--- /dev/null
+++ b/arch/x86/kernel/pvclock.c
@@ -0,0 +1,146 @@
+/* paravirtual clock -- common code used by kvm/xen
+
+ This program is free software; you can redistribute it and/or modify
+ it under the terms of the GNU General Public License as published by
+ the Free Software Foundation; either version 2 of the License, or
+ (at your option) any later version.
+
+ This program is distributed in the hope that it will be useful,
+ but WITHOUT ANY WARRANTY; without even the implied warranty of
+ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ GNU General Public License for more details.
+
+ You should have received a copy of the GNU General Public License
+ along with this program; if not, write to the Free Software
+ Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
+*/
+
+#include <linux/kernel.h>
+#include <linux/percpu.h>
+#include <asm/pvclock.h>
+
+/*
+ * These are perodically updated
+ * xen: magic shared_info page
+ * kvm: gpa registered via msr
+ * and then copied here.
+ */
+struct pvclock_shadow_time {
+ u64 tsc_timestamp; /* TSC at last update of time vals. */
+ u64 system_timestamp; /* Time, in nanosecs, since boot. */
+ u32 tsc_to_nsec_mul;
+ int tsc_shift;
+ u32 version;
+};
+
+/*
+ * Scale a 64-bit delta by scaling and multiplying by a 32-bit fraction,
+ * yielding a 64-bit result.
+ */
+static inline u64 scale_delta(u64 delta, u32 mul_frac, int shift)
+{
+ u64 product;
+#ifdef __i386__
+ u32 tmp1, tmp2;
+#endif
+
+ if (shift < 0)
+ delta >>= -shift;
+ else
+ delta <<= shift;
+
+#ifdef __i386__
+ __asm__ (
+ "mul %5 ; "
+ "mov %4,%%eax ; "
+ "mov %%edx,%4 ; "
+ "mul %5 ; "
+ "xor %5,%5 ; "
+ "add %4,%%eax ; "
+ "adc %5,%%edx ; "
+ : "=A" (product), "=r" (tmp1), "=r" (tmp2)
+ : "a" ((u32)delta), "1" ((u32)(delta >> 32)), "2" (mul_frac) );
+#elif __x86_64__
+ __asm__ (
+ "mul %%rdx ; shrd $32,%%rdx,%%rax"
+ : "=a" (product) : "0" (delta), "d" ((u64)mul_frac) );
+#else
+#error implement me!
+#endif
+
+ return product;
+}
+
+static u64 pvclock_get_nsec_offset(struct pvclock_shadow_time *shadow)
+{
+ u64 delta = native_read_tsc() - shadow->tsc_timestamp;
+ return scale_delta(delta, shadow->tsc_to_nsec_mul, shadow->tsc_shift);
+}
+
+/*
+ * Reads a consistent set of time-base values from hypervisor,
+ * into a shadow data area.
+ */
+static unsigned pvclock_get_time_values(struct pvclock_shadow_time *dst,
+ struct kvm_vcpu_time_info *src)
+{
+ do {
+ dst->version = src->version;
+ rmb(); /* fetch version before data */
+ dst->tsc_timestamp = src->tsc_timestamp;
+ dst->system_timestamp = src->system_time;
+ dst->tsc_to_nsec_mul = src->tsc_to_system_mul;
+ dst->tsc_shift = src->tsc_shift;
+ rmb(); /* test version after fetching data */
+ } while ((src->version & 1) | (dst->version ^ src->version));
+
+ return dst->version;
+}
+
+/*
+ * This is our read_clock function. The host puts an tsc timestamp each time
+ * it updates a new time. Without the tsc adjustment, we can have a situation
+ * in which a vcpu starts to run earlier (smaller system_time), but probes
+ * time later (compared to another vcpu), leading to backwards time
+ */
+cycle_t pvclock_clocksource_read(struct kvm_vcpu_time_info *src)
+{
+ struct pvclock_shadow_time shadow;
+ unsigned version;
+ cycle_t ret;
+
+ do {
+ version = pvclock_get_time_values(&shadow, src);
+ barrier();
+ ret = shadow.system_timestamp + pvclock_get_nsec_offset(&shadow);
+ barrier();
+ } while (version != src->version);
+
+ return ret;
+}
+
+void pvclock_read_wallclock(struct kvm_wall_clock *wall_clock,
+ struct kvm_vcpu_time_info *vcpu_time,
+ struct timespec *ts)
+{
+ u32 version;
+ u64 delta;
+ struct timespec now;
+
+ /* get wallclock at system boot */
+ do {
+ version = wall_clock->wc_version;
+ rmb(); /* fetch version before time */
+ now.tv_sec = wall_clock->wc_sec;
+ now.tv_nsec = wall_clock->wc_nsec;
+ rmb(); /* fetch time before checking version */
+ } while ((wall_clock->wc_version & 1) || (version != wall_clock->wc_version));
+
+ delta = pvclock_clocksource_read(vcpu_time); /* time since system boot */
+ delta += now.tv_sec * (u64)NSEC_PER_SEC + now.tv_nsec;
+
+ now.tv_nsec = do_div(delta, NSEC_PER_SEC);
+ now.tv_sec = delta;
+
+ set_normalized_timespec(ts, now.tv_sec, now.tv_nsec);
+}
diff --git a/include/asm-x86/pvclock.h b/include/asm-x86/pvclock.h
new file mode 100644
index 0000000..2b9812f
--- /dev/null
+++ b/include/asm-x86/pvclock.h
@@ -0,0 +1,6 @@
+#include <linux/clocksource.h>
+#include <asm/kvm_para.h>
+cycle_t pvclock_clocksource_read(struct kvm_vcpu_time_info *src);
+void pvclock_read_wallclock(struct kvm_wall_clock *wall,
+ struct kvm_vcpu_time_info *vcpu,
+ struct timespec *ts);
--
1.5.4.1