Excerpts from Christophe Leroy's message of August 5, 2021 5:22 pm:
>
>
> Le 26/07/2021 à 05:49, Nicholas Piggin a écrit :
>> Rather than have KVM look up the host timer and fiddle with the
>> irq-work internal details, have the powerpc/time.c code provide a
>> function for KVM to re-arm the Linux timer code when exiting a
>> guest.
>>
>> This is implementation has an improvement over existing code of
>> marking a decrementer interrupt as soft-pending if a timer has
>> expired, rather than setting DEC to a -ve value, which tended to
>> cause host timers to take two interrupts (first hdec to exit the
>> guest, then the immediate dec).
>>
>> Signed-off-by: Nicholas Piggin <npiggin@xxxxxxxxx>
>> ---
>> arch/powerpc/include/asm/time.h | 16 +++-------
>> arch/powerpc/kernel/time.c | 52 +++++++++++++++++++++++++++------
>> arch/powerpc/kvm/book3s_hv.c | 7 ++---
>> 3 files changed, 49 insertions(+), 26 deletions(-)
>>
>> diff --git a/arch/powerpc/include/asm/time.h b/arch/powerpc/include/asm/time.h
>> index 69b6be617772..924b2157882f 100644
>> --- a/arch/powerpc/include/asm/time.h
>> +++ b/arch/powerpc/include/asm/time.h
>> @@ -99,18 +99,6 @@ extern void div128_by_32(u64 dividend_high, u64 dividend_low,
>> extern void secondary_cpu_time_init(void);
>> extern void __init time_init(void);
>>
>> -#ifdef CONFIG_PPC64
>> -static inline unsigned long test_irq_work_pending(void)
>> -{
>> - unsigned long x;
>> -
>> - asm volatile("lbz %0,%1(13)"
>> - : "=r" (x)
>> - : "i" (offsetof(struct paca_struct, irq_work_pending)));
>> - return x;
>> -}
>> -#endif
>> -
>> DECLARE_PER_CPU(u64, decrementers_next_tb);
>>
>> static inline u64 timer_get_next_tb(void)
>> @@ -118,6 +106,10 @@ static inline u64 timer_get_next_tb(void)
>> return __this_cpu_read(decrementers_next_tb);
>> }
>>
>> +#ifdef CONFIG_KVM_BOOK3S_HV_POSSIBLE
>> +void timer_rearm_host_dec(u64 now);
>> +#endif
>> +
>> /* 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 72d872b49167..016828b7401b 100644
>> --- a/arch/powerpc/kernel/time.c
>> +++ b/arch/powerpc/kernel/time.c
>> @@ -499,6 +499,16 @@ EXPORT_SYMBOL(profile_pc);
>> * 64-bit uses a byte in the PACA, 32-bit uses a per-cpu variable...
>> */
>> #ifdef CONFIG_PPC64
>> +static inline unsigned long test_irq_work_pending(void)
>> +{
>> + unsigned long x;
>> +
>> + asm volatile("lbz %0,%1(13)"
>> + : "=r" (x)
>> + : "i" (offsetof(struct paca_struct, irq_work_pending)));
>
> Can we just use READ_ONCE() instead of hard coding the read ?
Good question, probably yes. Probably calls for its own patch series,
e.g., hw_irq.h has all similar paca accesses.
Thanks,
Nick
