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[v1,08/55] KVM: PPC: Book3S HV P9: Use host timer accounting to avoid decrementer read

Message ID 20210726035036.739609-9-npiggin@gmail.com
State New
Headers show
Series [v1,01/55] KVM: PPC: Book3S HV: Remove TM emulation from POWER7/8 path | expand

Commit Message

Nicholas Piggin July 26, 2021, 3:49 a.m. UTC 
There is no need to save away the host DEC value, as it is derived
from the host timer subsystem which maintains the next timer time,
so it can be restored from there.

Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
---
 arch/powerpc/include/asm/time.h |  5 +++++
 arch/powerpc/kernel/time.c      |  1 +
 arch/powerpc/kvm/book3s_hv.c    | 14 +++++++-------
 3 files changed, 13 insertions(+), 7 deletions(-)
diff mbox series

Patch

diff --git a/arch/powerpc/include/asm/time.h b/arch/powerpc/include/asm/time.h
index 8c2c3dd4ddba..fd09b4797fd7 100644
--- a/arch/powerpc/include/asm/time.h
+++ b/arch/powerpc/include/asm/time.h
@@ -111,6 +111,11 @@  static inline unsigned long test_irq_work_pending(void)
 
 DECLARE_PER_CPU(u64, decrementers_next_tb);
 
+static inline u64 timer_get_next_tb(void)
+{
+	return __this_cpu_read(decrementers_next_tb);
+}
+
 /* 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 e45ce427bffb..01df89918aa4 100644
--- a/arch/powerpc/kernel/time.c
+++ b/arch/powerpc/kernel/time.c
@@ -108,6 +108,7 @@  struct clock_event_device decrementer_clockevent = {
 EXPORT_SYMBOL(decrementer_clockevent);
 
 DEFINE_PER_CPU(u64, decrementers_next_tb);
+EXPORT_SYMBOL_GPL(decrementers_next_tb);
 static DEFINE_PER_CPU(struct clock_event_device, decrementers);
 
 #define XSEC_PER_SEC (1024*1024)
diff --git a/arch/powerpc/kvm/book3s_hv.c b/arch/powerpc/kvm/book3s_hv.c
index 7020cbbf3aa1..82976f734bd1 100644
--- a/arch/powerpc/kvm/book3s_hv.c
+++ b/arch/powerpc/kvm/book3s_hv.c
@@ -3829,18 +3829,17 @@  static int kvmhv_p9_guest_entry(struct kvm_vcpu *vcpu, u64 time_limit,
 	struct kvmppc_vcore *vc = vcpu->arch.vcore;
 	struct p9_host_os_sprs host_os_sprs;
 	s64 dec;
-	u64 tb;
+	u64 tb, next_timer;
 	int trap, save_pmu;
 
 	WARN_ON_ONCE(vcpu->arch.ceded);
 
-	dec = mfspr(SPRN_DEC);
 	tb = mftb();
-	if (dec < 0)
+	next_timer = timer_get_next_tb();
+	if (tb >= next_timer)
 		return BOOK3S_INTERRUPT_HV_DECREMENTER;
-	local_paca->kvm_hstate.dec_expires = dec + tb;
-	if (local_paca->kvm_hstate.dec_expires < time_limit)
-		time_limit = local_paca->kvm_hstate.dec_expires;
+	if (next_timer < time_limit)
+		time_limit = next_timer;
 
 	save_p9_host_os_sprs(&host_os_sprs);
 
@@ -4019,7 +4018,8 @@  static int kvmhv_p9_guest_entry(struct kvm_vcpu *vcpu, u64 time_limit,
 	vc->entry_exit_map = 0x101;
 	vc->in_guest = 0;
 
-	set_dec(local_paca->kvm_hstate.dec_expires - mftb());
+	next_timer = timer_get_next_tb();
+	set_dec(next_timer - mftb());
 	/* We may have raced with new irq work */
 	if (test_irq_work_pending())
 		set_dec(1);