Commit 25aa1458 authored by Nicholas Piggin's avatar Nicholas Piggin Committed by Michael Ellerman
Browse files

powerpc/time: add API for KVM to re-arm the host timer/decrementer 



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: default avatarNicholas Piggin <npiggin@gmail.com>
Signed-off-by: default avatarMichael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20211123095231.1036501-8-npiggin@gmail.com
parent 34bf08a2

arch/powerpc/include/asm/time.h

+4 −12
Original line number Diff line number Diff line
@@ -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);

arch/powerpc/kernel/time.c

+43 −9
Original line number Diff line number Diff line
@@ -498,6 +498,16 @@ 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)));

	return x;

}



static inline void set_irq_work_pending_flag(void)

{

	asm volatile("stb %0,%1(13)" : :
@@ -541,13 +551,44 @@ 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.
@@ -608,10 +649,7 @@ 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);

	}
@@ -845,11 +883,7 @@ 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;

}

arch/powerpc/kvm/book3s_hv.c

+2 −5
Original line number Diff line number Diff line
@@ -4062,11 +4062,8 @@ 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();