Re: [PATCH V11 11/17] RISC-V: paravirt: pvqspinlock: Add paravirt qspinlock skeleton

[Guo Ren <guoren@kernel.org>]

On Fri, Sep 15, 2023 at 1:42 PM Leonardo Bras <leobras@redhat.com> wrote:
>
> On Sun, Sep 10, 2023 at 04:29:05AM -0400, guoren@kernel.org wrote:
> > From: Guo Ren <guoren@linux.alibaba.com>
> >
> > Using static_call to switch between:
> >   native_queued_spin_lock_slowpath()    __pv_queued_spin_lock_slowpath()
> >   native_queued_spin_unlock()           __pv_queued_spin_unlock()
> >
> > Finish the pv_wait implementation, but pv_kick needs the SBI
> > definition of the next patches.
> >
> > Signed-off-by: Guo Ren <guoren@linux.alibaba.com>
> > Signed-off-by: Guo Ren <guoren@kernel.org>
> > ---
> >  arch/riscv/include/asm/Kbuild               |  1 -
> >  arch/riscv/include/asm/qspinlock.h          | 35 +++++++++++++
> >  arch/riscv/include/asm/qspinlock_paravirt.h | 29 +++++++++++
> >  arch/riscv/include/asm/spinlock.h           |  2 +-
> >  arch/riscv/kernel/qspinlock_paravirt.c      | 57 +++++++++++++++++++++
> >  arch/riscv/kernel/setup.c                   |  4 ++
> >  6 files changed, 126 insertions(+), 2 deletions(-)
> >  create mode 100644 arch/riscv/include/asm/qspinlock.h
> >  create mode 100644 arch/riscv/include/asm/qspinlock_paravirt.h
> >  create mode 100644 arch/riscv/kernel/qspinlock_paravirt.c
> >
> > diff --git a/arch/riscv/include/asm/Kbuild b/arch/riscv/include/asm/Kbuild
> > index a0dc85e4a754..b89cb3b73c13 100644
> > --- a/arch/riscv/include/asm/Kbuild
> > +++ b/arch/riscv/include/asm/Kbuild
> > @@ -7,6 +7,5 @@ generic-y += parport.h
> >  generic-y += spinlock_types.h
> >  generic-y += qrwlock.h
> >  generic-y += qrwlock_types.h
> > -generic-y += qspinlock.h
> >  generic-y += user.h
> >  generic-y += vmlinux.lds.h
> > diff --git a/arch/riscv/include/asm/qspinlock.h b/arch/riscv/include/asm/qspinlock.h
> > new file mode 100644
> > index 000000000000..7d4f416c908c
> > --- /dev/null
> > +++ b/arch/riscv/include/asm/qspinlock.h
> > @@ -0,0 +1,35 @@
> > +/* SPDX-License-Identifier: GPL-2.0 */
> > +/*
> > + * Copyright (c), 2023 Alibaba Cloud
> > + * Authors:
> > + *   Guo Ren <guoren@linux.alibaba.com>
> > + */
> > +
> > +#ifndef _ASM_RISCV_QSPINLOCK_H
> > +#define _ASM_RISCV_QSPINLOCK_H
> > +
> > +#ifdef CONFIG_PARAVIRT_SPINLOCKS
> > +#include <asm/qspinlock_paravirt.h>
> > +
> > +/* How long a lock should spin before we consider blocking */
> > +#define SPIN_THRESHOLD               (1 << 15)
> > +
> > +void native_queued_spin_lock_slowpath(struct qspinlock *lock, u32 val);
> > +void __pv_init_lock_hash(void);
> > +void __pv_queued_spin_lock_slowpath(struct qspinlock *lock, u32 val);
> > +
> > +static inline void queued_spin_lock_slowpath(struct qspinlock *lock, u32 val)
> > +{
> > +     static_call(pv_queued_spin_lock_slowpath)(lock, val);
> > +}
> > +
> > +#define queued_spin_unlock   queued_spin_unlock
> > +static inline void queued_spin_unlock(struct qspinlock *lock)
> > +{
> > +     static_call(pv_queued_spin_unlock)(lock);
> > +}
> > +#endif /* CONFIG_PARAVIRT_SPINLOCKS */
> > +
> > +#include <asm-generic/qspinlock.h>
> > +
> > +#endif /* _ASM_RISCV_QSPINLOCK_H */
> > diff --git a/arch/riscv/include/asm/qspinlock_paravirt.h b/arch/riscv/include/asm/qspinlock_paravirt.h
> > new file mode 100644
> > index 000000000000..9681e851f69d
> > --- /dev/null
> > +++ b/arch/riscv/include/asm/qspinlock_paravirt.h
> > @@ -0,0 +1,29 @@
> > +/* SPDX-License-Identifier: GPL-2.0 */
> > +/*
> > + * Copyright (c), 2023 Alibaba Cloud
> > + * Authors:
> > + *   Guo Ren <guoren@linux.alibaba.com>
> > + */
> > +
> > +#ifndef _ASM_RISCV_QSPINLOCK_PARAVIRT_H
> > +#define _ASM_RISCV_QSPINLOCK_PARAVIRT_H
> > +
> > +void pv_wait(u8 *ptr, u8 val);
> > +void pv_kick(int cpu);
> > +
> > +void dummy_queued_spin_lock_slowpath(struct qspinlock *lock, u32 val);
> > +void dummy_queued_spin_unlock(struct qspinlock *lock);
> > +
> > +DECLARE_STATIC_CALL(pv_queued_spin_lock_slowpath, dummy_queued_spin_lock_slowpath);
> > +DECLARE_STATIC_CALL(pv_queued_spin_unlock, dummy_queued_spin_unlock);
> > +
> > +void __init pv_qspinlock_init(void);
> > +
> > +static inline bool pv_is_native_spin_unlock(void)
> > +{
> > +     return false;
> > +}
> > +
> > +void __pv_queued_spin_unlock(struct qspinlock *lock);
> > +
> > +#endif /* _ASM_RISCV_QSPINLOCK_PARAVIRT_H */
> > diff --git a/arch/riscv/include/asm/spinlock.h b/arch/riscv/include/asm/spinlock.h
> > index 6b38d6616f14..ed4253f491fe 100644
> > --- a/arch/riscv/include/asm/spinlock.h
> > +++ b/arch/riscv/include/asm/spinlock.h
> > @@ -39,7 +39,7 @@ static inline bool virt_spin_lock(struct qspinlock *lock)
> >  #undef arch_spin_trylock
> >  #undef arch_spin_unlock
> >
> > -#include <asm-generic/qspinlock.h>
> > +#include <asm/qspinlock.h>
> >  #include <linux/jump_label.h>
> >
> >  #undef arch_spin_is_locked
> > diff --git a/arch/riscv/kernel/qspinlock_paravirt.c b/arch/riscv/kernel/qspinlock_paravirt.c
> > new file mode 100644
> > index 000000000000..85ff5a3ec234
> > --- /dev/null
> > +++ b/arch/riscv/kernel/qspinlock_paravirt.c
> > @@ -0,0 +1,57 @@
> > +// SPDX-License-Identifier: GPL-2.0
> > +/*
> > + * Copyright (c), 2023 Alibaba Cloud
> > + * Authors:
> > + *   Guo Ren <guoren@linux.alibaba.com>
> > + */
> > +
> > +#include <linux/static_call.h>
> > +#include <asm/qspinlock_paravirt.h>
> > +#include <asm/sbi.h>
> > +
> > +void pv_kick(int cpu)
> > +{
> > +     return;
> > +}
> > +
> > +void pv_wait(u8 *ptr, u8 val)
> > +{
> > +     unsigned long flags;
> > +
> > +     if (in_nmi())
> > +             return;
> > +
> > +     local_irq_save(flags);
> > +     if (READ_ONCE(*ptr) != val)
> > +             goto out;
> > +
> > +     /* wait_for_interrupt(); */
> > +out:
> > +     local_irq_restore(flags);
> > +}
> > +
> > +static void native_queued_spin_unlock(struct qspinlock *lock)
> > +{
> > +     smp_store_release(&lock->locked, 0);
> > +}
> > +
> > +DEFINE_STATIC_CALL(pv_queued_spin_lock_slowpath, native_queued_spin_lock_slowpath);
> > +EXPORT_STATIC_CALL(pv_queued_spin_lock_slowpath);
> > +
> > +DEFINE_STATIC_CALL(pv_queued_spin_unlock, native_queued_spin_unlock);
> > +EXPORT_STATIC_CALL(pv_queued_spin_unlock);
> > +
> > +void __init pv_qspinlock_init(void)
> > +{
> > +     if (num_possible_cpus() == 1)
> > +             return;
> > +
> > +     if(sbi_get_firmware_id() != SBI_EXT_BASE_IMPL_ID_KVM)
>
> Checks like this seem to be very common on this patchset.
> For someone not much familiar with this, it can be hard to
> understand.
>
> I mean, on patch 8/17 you introduce those IDs, which look to be
> incremental ( ID == N includes stuff from ID < N ), but I am not sure as I
> couln't find much documentation on that.
It's from sbi spec:
https://github.com/riscv-non-isa/riscv-sbi-doc/releases

0 Berkeley Boot Loader (BBL)
1 OpenSBI
2 Xvisor
3 KVM
4 RustSBI
5 Diosix
6 Coffer
7 Xen Project
8 PolarFire Hart Software Service

>
> Then above you test for the id being different than
> SBI_EXT_BASE_IMPL_ID_KVM, but if they are actually incremental and a new
> version lands, the new version will also return early because it passes the
> test.
>
> I am no sure if above is right, but it's all I could understand without
> documentation.
>
> Well, my point is: this seems hard to understand & review, so it would be
> nice to have a macro like this to be used instead:
>
> #define sbi_fw_implements_kvm() \
>         (sbi_get_firmware_id() >= SBI_EXT_BASE_IMPL_ID_KVM)
No, it's not correct. It must be:
(sbi_get_firmware_id() == SBI_EXT_BASE_IMPL_ID_KVM)

>
> if(!sbi_fw_implements_kvm())
I'm okay with sbi_fw_implements_kvm().

>         return;
>
> What do you think?
>
> Other than that, LGTM.
>
> Thanks!
> Leo
>
> > +             return;
> > +
> > +     pr_info("PV qspinlocks enabled\n");
> > +     __pv_init_lock_hash();
> > +
> > +     static_call_update(pv_queued_spin_lock_slowpath, __pv_queued_spin_lock_slowpath);
> > +     static_call_update(pv_queued_spin_unlock, __pv_queued_spin_unlock);
> > +}
> > diff --git a/arch/riscv/kernel/setup.c b/arch/riscv/kernel/setup.c
> > index c57d15b05160..88690751f2ee 100644
> > --- a/arch/riscv/kernel/setup.c
> > +++ b/arch/riscv/kernel/setup.c
> > @@ -321,6 +321,10 @@ static void __init riscv_spinlock_init(void)
> >  #ifdef CONFIG_QUEUED_SPINLOCKS
> >       virt_spin_lock_init();
> >  #endif
> > +
> > +#ifdef CONFIG_PARAVIRT_SPINLOCKS
> > +     pv_qspinlock_init();
> > +#endif
> >  }
> >
> >  extern void __init init_rt_signal_env(void);
> > --
> > 2.36.1
> >
>


-- 
Best Regards
 Guo Ren