Commit 9581991a authored by Nicholas Piggin's avatar Nicholas Piggin Committed by Michael Ellerman
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KVM: PPC: Book3S HV P9: Use large decrementer for HDEC 



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: default avatarNicholas Piggin <npiggin@gmail.com>
Reviewed-by: default avatarAlexey Kardashevskiy <aik@ozlabs.ru>
Signed-off-by: default avatarMichael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20211123095231.1036501-6-npiggin@gmail.com
parent 4ebbd075

arch/powerpc/include/asm/time.h

+2 −0
Original line number Diff line number Diff line
@@ -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;

arch/powerpc/kernel/time.c

+1 −0
Original line number Diff line number Diff line
@@ -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);

arch/powerpc/kvm/book3s_hv_p9_entry.c

+2 −1
Original line number Diff line number Diff line
@@ -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);