Re: [PATCH v4 24/46] KVM: PPC: Book3S HV P9: Use large decrementer for HDEC
From: Alexey Kardashevskiy <hidden>
Date: 2021-03-26 02:05:52
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 <redacted> Signed-off-by: Nicholas Piggin <npiggin@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);
quoted hunk ↗ jump to hunk
--- 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