diff --git a/xen/arch/x86/cpu/common.c b/xen/arch/x86/cpu/common.c
index 4be86e1f7b..d045ed6b41 100644
--- a/xen/arch/x86/cpu/common.c
+++ b/xen/arch/x86/cpu/common.c
@@ -19,6 +19,7 @@
 #include <asm/random.h>
 #include <asm/setup.h>
 #include <asm/shstk.h>
+#include <asm/time.h>
 #include <asm/xstate.h>
 
 #include <public/sysctl.h>
@@ -444,6 +445,39 @@ void __init early_cpu_init(bool verbose)
 
 	if (!(c->vendor & (X86_VENDOR_AMD | X86_VENDOR_HYGON)))
 		park_offline_cpus = opt_mce;
+
+	/*
+	 * If nominal freq isn't available, use highest, thus causing NOW()
+	 * output to move more slowly.  See preset_tsc_scale().
+	 */
+	if (c->cpuid_level >= 0x15) {
+		cpuid(0x15, &eax, &ebx, &ecx, &edx);
+
+		if (ecx && ebx && eax)
+			preset_tsc_scale(DIV_ROUND_UP(ecx * 1UL * ebx, eax));
+		else if (c->cpuid_level >= 0x16) {
+			/* Assume CPU base freq ≈ TSC freq. */
+			cpuid(0x16, &eax, &ebx, &ecx, &edx);
+			if (eax)
+				preset_tsc_scale(eax * 1000000UL);
+			else if (ebx)
+				preset_tsc_scale(ebx * 1000000UL);
+		}
+	} else if (c->vendor & (X86_VENDOR_AMD | X86_VENDOR_HYGON)) {
+		unsigned int nom_mhz = 0, hi_mhz = 0;
+
+		amd_process_freq(c, NULL, &nom_mhz, &hi_mhz);
+		if (nom_mhz)
+			preset_tsc_scale(nom_mhz * 1000000UL);
+		else if (hi_mhz)
+			preset_tsc_scale(hi_mhz * 1000000UL);
+	} else if (c->vendor & X86_VENDOR_INTEL) {
+		unsigned int hi_mhz = 0;
+
+		intel_process_freq(c, NULL, &hi_mhz);
+		if (hi_mhz)
+			preset_tsc_scale(hi_mhz * 1000000UL);
+	}
 }
 
 void reset_cpuinfo(struct cpuinfo_x86 *c, bool keep_basic)
diff --git a/xen/arch/x86/cpu/intel.c b/xen/arch/x86/cpu/intel.c
index 5c07140695..1006126bc3 100644
--- a/xen/arch/x86/cpu/intel.c
+++ b/xen/arch/x86/cpu/intel.c
@@ -476,8 +476,8 @@ static int num_cpu_cores(struct cpuinfo_x86 *c)
 		return 1;
 }
 
-static void intel_process_freq(const struct cpuinfo_x86 *c,
-                               unsigned int *min_mhz, unsigned int *max_mhz)
+void intel_process_freq(const struct cpuinfo_x86 *c,
+                        unsigned int *min_mhz, unsigned int *max_mhz)
 {
     uint64_t msrval;
     uint8_t max_ratio, min_ratio;
diff --git a/xen/arch/x86/include/asm/processor.h b/xen/arch/x86/include/asm/processor.h
index 4b200428be..4b17e13a97 100644
--- a/xen/arch/x86/include/asm/processor.h
+++ b/xen/arch/x86/include/asm/processor.h
@@ -417,6 +417,9 @@ static inline uint8_t get_cpu_family(uint32_t raw, uint8_t *model,
     return fam;
 }
 
+void intel_process_freq(const struct cpuinfo_x86 *c,
+                        unsigned int *min_mhz, unsigned int *max_mhz);
+
 #ifdef CONFIG_INTEL
 extern int8_t opt_tsx;
 extern bool rtm_disabled;
diff --git a/xen/arch/x86/include/asm/time.h b/xen/arch/x86/include/asm/time.h
index ed763ebc1b..6c8f0fe58c 100644
--- a/xen/arch/x86/include/asm/time.h
+++ b/xen/arch/x86/include/asm/time.h
@@ -23,6 +23,7 @@ mktime (unsigned int year, unsigned int mon,
 int time_suspend(void);
 int time_resume(void);
 
+void preset_tsc_scale(unsigned long freq);
 void init_percpu_time(void);
 void time_latch_stamps(void);
 
diff --git a/xen/arch/x86/time.c b/xen/arch/x86/time.c
index f35555f185..f37fddc61e 100644
--- a/xen/arch/x86/time.c
+++ b/xen/arch/x86/time.c
@@ -1713,6 +1713,9 @@ s_time_t get_s_time_fixed(uint64_t at_tsc)
     const struct cpu_time *t = &this_cpu(cpu_time);
     uint64_t tsc, delta;
 
+    /* scale_delta() degenerates when the scale wasn't set yet. */
+    ASSERT(t->tsc_scale.mul_frac);
+
     if ( at_tsc )
         tsc = at_tsc;
     else
@@ -1728,6 +1731,20 @@ s_time_t get_s_time_fixed(uint64_t at_tsc)
 
 s_time_t get_s_time(void)
 {
+    /*
+     * Before the TSC scale is set, avoid returning constant 0 (or whatever
+     * this_cpu(cpu_time).stamp.local_stime is set to).  While the returned
+     * value is in no way representing time, it at least increases
+     * monotonically, thus avoiding e.g. waiting loops to degenerate to
+     * entirely infinite ones.
+     */
+    if ( unlikely(!this_cpu(cpu_time).tsc_scale.mul_frac) )
+    {
+        static s_time_t counter;
+
+        return arch_fetch_and_add(&counter, 1);
+    }
+
     return get_s_time_fixed(0);
 }
 
@@ -2681,6 +2698,22 @@ int __init init_xen_time(void)
     return 0;
 }
 
+/* BSP-only function to pre-set an approximate TSC scale. */
+void __init preset_tsc_scale(unsigned long freq)
+{
+    struct cpu_time *t = &this_cpu(cpu_time);
+
+    /*
+     * The incoming frequency is only approximate (nominal).  Increase it by
+     * 1% to make NOW() output rather a little too slow than too fast, thus
+     * avoiding a possible backwards jump once the final scale is set.
+     */
+    freq += DIV_ROUND_UP(freq, 100);
+
+    set_time_scale(&t->tsc_scale, freq);
+    t->stamp.local_tsc = boot_tsc_stamp;
+    NOW_good = true;
+}
 
 /* Early init function. */
 void __init early_time_init(void)
@@ -2698,6 +2731,9 @@ void __init early_time_init(void)
                    "TSC ADJUST set to %lx on boot CPU - clearing\n", tmp);
             wrmsrl(MSR_IA32_TSC_ADJUST, 0);
             boot_tsc_stamp -= tmp;
+
+            if ( t->stamp.local_tsc )
+                t->stamp.local_tsc -= tmp;
         }
     }