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Diffstat (limited to 'arch/x86/entry/vdso/vclock_gettime.c')
-rw-r--r--arch/x86/entry/vdso/vclock_gettime.c151
1 files changed, 73 insertions, 78 deletions
diff --git a/arch/x86/entry/vdso/vclock_gettime.c b/arch/x86/entry/vdso/vclock_gettime.c
index ca94fa649251..1a50e09c945b 100644
--- a/arch/x86/entry/vdso/vclock_gettime.c
+++ b/arch/x86/entry/vdso/vclock_gettime.c
@@ -17,8 +17,10 @@
#include <asm/vvar.h>
#include <asm/unistd.h>
#include <asm/msr.h>
+#include <asm/pvclock.h>
#include <linux/math64.h>
#include <linux/time.h>
+#include <linux/kernel.h>
#define gtod (&VVAR(vsyscall_gtod_data))
@@ -36,12 +38,12 @@ static notrace cycle_t vread_hpet(void)
}
#endif
-#ifndef BUILD_VDSO32
+#ifdef CONFIG_PARAVIRT_CLOCK
+extern u8 pvclock_page
+ __attribute__((visibility("hidden")));
+#endif
-#include <linux/kernel.h>
-#include <asm/vsyscall.h>
-#include <asm/fixmap.h>
-#include <asm/pvclock.h>
+#ifndef BUILD_VDSO32
notrace static long vdso_fallback_gettime(long clock, struct timespec *ts)
{
@@ -60,75 +62,6 @@ notrace static long vdso_fallback_gtod(struct timeval *tv, struct timezone *tz)
return ret;
}
-#ifdef CONFIG_PARAVIRT_CLOCK
-
-static notrace const struct pvclock_vsyscall_time_info *get_pvti(int cpu)
-{
- const struct pvclock_vsyscall_time_info *pvti_base;
- int idx = cpu / (PAGE_SIZE/PVTI_SIZE);
- int offset = cpu % (PAGE_SIZE/PVTI_SIZE);
-
- BUG_ON(PVCLOCK_FIXMAP_BEGIN + idx > PVCLOCK_FIXMAP_END);
-
- pvti_base = (struct pvclock_vsyscall_time_info *)
- __fix_to_virt(PVCLOCK_FIXMAP_BEGIN+idx);
-
- return &pvti_base[offset];
-}
-
-static notrace cycle_t vread_pvclock(int *mode)
-{
- const struct pvclock_vsyscall_time_info *pvti;
- cycle_t ret;
- u64 last;
- u32 version;
- u8 flags;
- unsigned cpu, cpu1;
-
-
- /*
- * Note: hypervisor must guarantee that:
- * 1. cpu ID number maps 1:1 to per-CPU pvclock time info.
- * 2. that per-CPU pvclock time info is updated if the
- * underlying CPU changes.
- * 3. that version is increased whenever underlying CPU
- * changes.
- *
- */
- do {
- cpu = __getcpu() & VGETCPU_CPU_MASK;
- /* TODO: We can put vcpu id into higher bits of pvti.version.
- * This will save a couple of cycles by getting rid of
- * __getcpu() calls (Gleb).
- */
-
- pvti = get_pvti(cpu);
-
- version = __pvclock_read_cycles(&pvti->pvti, &ret, &flags);
-
- /*
- * Test we're still on the cpu as well as the version.
- * We could have been migrated just after the first
- * vgetcpu but before fetching the version, so we
- * wouldn't notice a version change.
- */
- cpu1 = __getcpu() & VGETCPU_CPU_MASK;
- } while (unlikely(cpu != cpu1 ||
- (pvti->pvti.version & 1) ||
- pvti->pvti.version != version));
-
- if (unlikely(!(flags & PVCLOCK_TSC_STABLE_BIT)))
- *mode = VCLOCK_NONE;
-
- /* refer to tsc.c read_tsc() comment for rationale */
- last = gtod->cycle_last;
-
- if (likely(ret >= last))
- return ret;
-
- return last;
-}
-#endif
#else
@@ -162,15 +95,77 @@ notrace static long vdso_fallback_gtod(struct timeval *tv, struct timezone *tz)
return ret;
}
+#endif
+
#ifdef CONFIG_PARAVIRT_CLOCK
+static notrace const struct pvclock_vsyscall_time_info *get_pvti0(void)
+{
+ return (const struct pvclock_vsyscall_time_info *)&pvclock_page;
+}
static notrace cycle_t vread_pvclock(int *mode)
{
- *mode = VCLOCK_NONE;
- return 0;
-}
-#endif
+ const struct pvclock_vcpu_time_info *pvti = &get_pvti0()->pvti;
+ cycle_t ret;
+ u64 tsc, pvti_tsc;
+ u64 last, delta, pvti_system_time;
+ u32 version, pvti_tsc_to_system_mul, pvti_tsc_shift;
+ /*
+ * Note: The kernel and hypervisor must guarantee that cpu ID
+ * number maps 1:1 to per-CPU pvclock time info.
+ *
+ * Because the hypervisor is entirely unaware of guest userspace
+ * preemption, it cannot guarantee that per-CPU pvclock time
+ * info is updated if the underlying CPU changes or that that
+ * version is increased whenever underlying CPU changes.
+ *
+ * On KVM, we are guaranteed that pvti updates for any vCPU are
+ * atomic as seen by *all* vCPUs. This is an even stronger
+ * guarantee than we get with a normal seqlock.
+ *
+ * On Xen, we don't appear to have that guarantee, but Xen still
+ * supplies a valid seqlock using the version field.
+ *
+ * We only do pvclock vdso timing at all if
+ * PVCLOCK_TSC_STABLE_BIT is set, and we interpret that bit to
+ * mean that all vCPUs have matching pvti and that the TSC is
+ * synced, so we can just look at vCPU 0's pvti.
+ */
+
+ do {
+ version = pvti->version;
+
+ smp_rmb();
+
+ if (unlikely(!(pvti->flags & PVCLOCK_TSC_STABLE_BIT))) {
+ *mode = VCLOCK_NONE;
+ return 0;
+ }
+
+ tsc = rdtsc_ordered();
+ pvti_tsc_to_system_mul = pvti->tsc_to_system_mul;
+ pvti_tsc_shift = pvti->tsc_shift;
+ pvti_system_time = pvti->system_time;
+ pvti_tsc = pvti->tsc_timestamp;
+
+ /* Make sure that the version double-check is last. */
+ smp_rmb();
+ } while (unlikely((version & 1) || version != pvti->version));
+
+ delta = tsc - pvti_tsc;
+ ret = pvti_system_time +
+ pvclock_scale_delta(delta, pvti_tsc_to_system_mul,
+ pvti_tsc_shift);
+
+ /* refer to vread_tsc() comment for rationale */
+ last = gtod->cycle_last;
+
+ if (likely(ret >= last))
+ return ret;
+
+ return last;
+}
#endif
notrace static cycle_t vread_tsc(void)