Re: [PATCH v1 11/55] powerpc/time: add API for KVM to re-arm the host timer/decrementer

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Le 26/07/2021 à 05:49, Nicholas Piggin a écrit :
Rather than have KVM look up the host timer and fiddle with the
irq-work internal details, have the powerpc/time.c code provide a
function for KVM to re-arm the Linux timer code when exiting a
guest.

This is implementation has an improvement over existing code of
marking a decrementer interrupt as soft-pending if a timer has
expired, rather than setting DEC to a -ve value, which tended to
cause host timers to take two interrupts (first hdec to exit the
guest, then the immediate dec).

Signed-off-by: Nicholas Piggin <npiggin@xxxxxxxxx>
---
  arch/powerpc/include/asm/time.h | 16 +++-------
  arch/powerpc/kernel/time.c      | 52 +++++++++++++++++++++++++++------
  arch/powerpc/kvm/book3s_hv.c    |  7 ++---
  3 files changed, 49 insertions(+), 26 deletions(-)

diff --git a/arch/powerpc/include/asm/time.h b/arch/powerpc/include/asm/time.h
index 69b6be617772..924b2157882f 100644
--- a/arch/powerpc/include/asm/time.h
+++ b/arch/powerpc/include/asm/time.h
@@ -99,18 +99,6 @@ extern void div128_by_32(u64 dividend_high, u64 dividend_low,
  extern void secondary_cpu_time_init(void);
  extern void __init time_init(void);
-#ifdef CONFIG_PPC64
-static inline unsigned long test_irq_work_pending(void)
-{
-	unsigned long x;
-
-	asm volatile("lbz %0,%1(13)"
-		: "=r" (x)
-		: "i" (offsetof(struct paca_struct, irq_work_pending)));
-	return x;
-}
-#endif
-
  DECLARE_PER_CPU(u64, decrementers_next_tb);
static inline u64 timer_get_next_tb(void)
@@ -118,6 +106,10 @@ static inline u64 timer_get_next_tb(void)
  	return __this_cpu_read(decrementers_next_tb);
  }
+#ifdef CONFIG_KVM_BOOK3S_HV_POSSIBLE
+void timer_rearm_host_dec(u64 now);
+#endif
+
  /* Convert timebase ticks to nanoseconds */
  unsigned long long tb_to_ns(unsigned long long tb_ticks);
diff --git a/arch/powerpc/kernel/time.c b/arch/powerpc/kernel/time.c
index 72d872b49167..016828b7401b 100644
--- a/arch/powerpc/kernel/time.c
+++ b/arch/powerpc/kernel/time.c
@@ -499,6 +499,16 @@ EXPORT_SYMBOL(profile_pc);
   * 64-bit uses a byte in the PACA, 32-bit uses a per-cpu variable...
   */
  #ifdef CONFIG_PPC64
+static inline unsigned long test_irq_work_pending(void)
+{
+	unsigned long x;
+
+	asm volatile("lbz %0,%1(13)"
+		: "=r" (x)
+		: "i" (offsetof(struct paca_struct, irq_work_pending)));

Can we just use READ_ONCE() instead of hard coding the read ?


+	return x;
+}
+
  static inline void set_irq_work_pending_flag(void)
  {
  	asm volatile("stb %0,%1(13)" : :
@@ -542,13 +552,44 @@ void arch_irq_work_raise(void)
  	preempt_enable();
  }
+static void set_dec_or_work(u64 val)
+{
+	set_dec(val);
+	/* We may have raced with new irq work */
+	if (unlikely(test_irq_work_pending()))
+		set_dec(1);
+}
+
  #else  /* CONFIG_IRQ_WORK */
#define test_irq_work_pending() 0
  #define clear_irq_work_pending()
+static void set_dec_or_work(u64 val)
+{
+	set_dec(val);
+}
  #endif /* CONFIG_IRQ_WORK */
+#ifdef CONFIG_KVM_BOOK3S_HV_POSSIBLE
+void timer_rearm_host_dec(u64 now)
+{
+	u64 *next_tb = this_cpu_ptr(&decrementers_next_tb);
+
+	WARN_ON_ONCE(!arch_irqs_disabled());
+	WARN_ON_ONCE(mfmsr() & MSR_EE);
+
+	if (now >= *next_tb) {
+		local_paca->irq_happened |= PACA_IRQ_DEC;
+	} else {
+		now = *next_tb - now;
+		if (now <= decrementer_max)
+			set_dec_or_work(now);
+	}
+}
+EXPORT_SYMBOL_GPL(timer_rearm_host_dec);
+#endif
+
  /*
   * timer_interrupt - gets called when the decrementer overflows,
   * with interrupts disabled.
@@ -609,10 +650,7 @@ DEFINE_INTERRUPT_HANDLER_ASYNC(timer_interrupt)
  	} else {
  		now = *next_tb - now;
  		if (now <= decrementer_max)
-			set_dec(now);
-		/* We may have raced with new irq work */
-		if (test_irq_work_pending())
-			set_dec(1);
+			set_dec_or_work(now);
  		__this_cpu_inc(irq_stat.timer_irqs_others);
  	}
@@ -854,11 +892,7 @@ static int decrementer_set_next_event(unsigned long evt,
  				      struct clock_event_device *dev)
  {
  	__this_cpu_write(decrementers_next_tb, get_tb() + evt);
-	set_dec(evt);
-
-	/* We may have raced with new irq work */
-	if (test_irq_work_pending())
-		set_dec(1);
+	set_dec_or_work(evt);
return 0;
  }
diff --git a/arch/powerpc/kvm/book3s_hv.c b/arch/powerpc/kvm/book3s_hv.c
index 6e6cfb10e9bb..0cef578930f9 100644
--- a/arch/powerpc/kvm/book3s_hv.c
+++ b/arch/powerpc/kvm/book3s_hv.c
@@ -4018,11 +4018,8 @@ static int kvmhv_p9_guest_entry(struct kvm_vcpu *vcpu, u64 time_limit,
  	vc->entry_exit_map = 0x101;
  	vc->in_guest = 0;
- next_timer = timer_get_next_tb();
-	set_dec(next_timer - tb);
-	/* We may have raced with new irq work */
-	if (test_irq_work_pending())
-		set_dec(1);
+	timer_rearm_host_dec(tb);
+
  	mtspr(SPRN_SPRG_VDSO_WRITE, local_paca->sprg_vdso);
kvmhv_load_host_pmu();




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