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KVM: PPC: Book3S HV P9: Use large decrementer for HDEC

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On processors that don't suppress the HDEC exceptions when LPCR[HDICE]=0,
this could help reduce needless guest exits due to leftover exceptions on
entering the guest.

Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Reviewed-by: Alexey Kardashevskiy <aik@ozlabs.ru>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20211123095231.1036501-6-npiggin@gmail.com
This commit is contained in:
Nicholas Piggin 2021-11-23 19:51:43 +10:00 committed by Michael Ellerman
parent 4ebbd075bc
commit 9581991a60
3 changed files with 5 additions and 1 deletions
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2
arch/powerpc/include/asm/time.h
View file

@ -18,6 +18,8 @@
#include <asm/vdso/timebase.h>
/* time.c */
extern u64 decrementer_max;
extern unsigned long tb_ticks_per_jiffy;
extern unsigned long tb_ticks_per_usec;
extern unsigned long tb_ticks_per_sec;

1
arch/powerpc/kernel/time.c
View file

@ -88,6 +88,7 @@ static struct clocksource clocksource_timebase = {
#define DECREMENTER_DEFAULT_MAX 0x7FFFFFFF
u64 decrementer_max = DECREMENTER_DEFAULT_MAX;
EXPORT_SYMBOL_GPL(decrementer_max); /* for KVM HDEC */
static int decrementer_set_next_event(unsigned long evt,
struct clock_event_device *dev);

3
arch/powerpc/kvm/book3s_hv_p9_entry.c
View file

@ -504,7 +504,8 @@ int kvmhv_vcpu_entry_p9(struct kvm_vcpu *vcpu, u64 time_limit, unsigned long lpc
vc->tb_offset_applied = 0;
}
mtspr(SPRN_HDEC, 0x7fffffff);
/* HDEC must be at least as large as DEC, so decrementer_max fits */
mtspr(SPRN_HDEC, decrementer_max);
save_clear_guest_mmu(kvm, vcpu);
switch_mmu_to_host(kvm, host_pidr);