[PATCH v4 24/46] KVM: PPC: Book3S HV P9: Use large decrementer for HDEC

[Alexey Kardashevskiy]

On 23/03/2021 12:02, Nicholas Piggin wrote:
> 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.
> 
> Reviewed-by: Alexey Kardashevskiy <aik at ozlabs.ru>
> Signed-off-by: Nicholas Piggin <npiggin at gmail.com>


ERROR: modpost: "decrementer_max" [arch/powerpc/kvm/kvm-hv.ko] undefined!


need this:

--- a/arch/powerpc/kernel/time.c
+++ b/arch/powerpc/kernel/time.c
@@ -89,6 +89,7 @@ static struct clocksource clocksource_timebase = {

  #define DECREMENTER_DEFAULT_MAX 0x7FFFFFFF
  u64 decrementer_max = DECREMENTER_DEFAULT_MAX;
+EXPORT_SYMBOL_GPL(decrementer_max);


> ---
>   arch/powerpc/include/asm/time.h | 2 ++
>   arch/powerpc/kvm/book3s_hv.c    | 3 ++-
>   2 files changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/powerpc/include/asm/time.h b/arch/powerpc/include/asm/time.h
> index 8dd3cdb25338..68d94711811e 100644
> --- a/arch/powerpc/include/asm/time.h
> +++ b/arch/powerpc/include/asm/time.h
> @@ -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;
> diff --git a/arch/powerpc/kvm/book3s_hv.c b/arch/powerpc/kvm/book3s_hv.c
> index 8215430e6d5e..bb30c5ab53d1 100644
> --- a/arch/powerpc/kvm/book3s_hv.c
> +++ b/arch/powerpc/kvm/book3s_hv.c
> @@ -3658,7 +3658,8 @@ static int kvmhv_load_hv_regs_and_go(struct kvm_vcpu *vcpu, u64 time_limit,
>   		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);
>   
>   	switch_mmu_to_host_radix(kvm, host_pidr);
>   
> 

-- 
Alexey