From: Sergey Senozhatsky <senozhatsky@chromium.org>
To: Marc Zyngier <maz@kernel.org>
Cc: Sergey Senozhatsky <senozhatsky@chromium.org>,
Will Deacon <will@kernel.org>,
Suleiman Souhlal <suleiman@google.com>,
Joel Fernandes <joelaf@google.com>,
linux-arm-kernel@lists.infradead.org,
kvmarm@lists.cs.columbia.edu, linux-kernel@vger.kernel.org,
virtualization@lists.linux-foundation.org
Subject: Re: [PATCHv2 2/4] arm64: add guest pvstate support
Date: Wed, 21 Jul 2021 11:05:25 +0900 [thread overview]
Message-ID: <YPeA5ReGSwBvWGSa@google.com> (raw)
In-Reply-To: <877dhv35ea.wl-maz@kernel.org>
On (21/07/12 16:42), Marc Zyngier wrote:
> >
> > PV-vcpu-state is a per-CPU struct, which, for the time being,
> > holds boolean `preempted' vCPU state. During the startup,
> > given that host supports PV-state, each guest vCPU sends
> > a pointer to its per-CPU variable to the host as a payload
>
> What is the expected memory type for this memory region? What is its
> life cycle? Where is it allocated from?
Guest per-CPU area, which physical addresses is shared with the host.
> > with the SMCCC HV call, so that host can update vCPU state
> > when it puts or loads vCPU.
> >
> > This has impact on the guest's scheduler:
> >
> > [..]
> > wake_up_process()
> > try_to_wake_up()
> > select_task_rq_fair()
> > available_idle_cpu()
> > vcpu_is_preempted()
> >
> > Some sched benchmarks data is available on the github page [0].
> >
> > [0] https://github.com/sergey-senozhatsky/arm64-vcpu_is_preempted
>
> Please include these results in the cover letter. I tend to reply to
> email while offline, and I can't comment on GH.
ACK.
> > +struct vcpu_state {
>
> If this is KVM specific (which it most likely is), please name-space
> it correctly, and move it to a KVM-specific location.
ACK.
> > + bool preempted;
> > + u8 reserved[63];
>
> Why 63? Do you attach any particular meaning to a 64byte structure
> (and before you say "cache line size", please look at some of the
> cache line sizes we have to deal with...).
We do have some future plans to share some bits of the guest's context
with the host.
> This should also be versioned from day-1, one way or another.
Makes sense.
> > +};
> > +
> > #ifdef CONFIG_PARAVIRT
> > #include <linux/static_call_types.h>
> >
> > @@ -20,8 +25,22 @@ static inline u64 paravirt_steal_clock(int cpu)
> >
> > int __init pv_time_init(void);
> >
> > +bool dummy_vcpu_is_preempted(unsigned int cpu);
> > +
> > +extern struct static_key pv_vcpu_is_preempted_enabled;
> > +DECLARE_STATIC_CALL(pv_vcpu_is_preempted, dummy_vcpu_is_preempted);
> > +
> > +static inline bool paravirt_vcpu_is_preempted(unsigned int cpu)
> > +{
> > + return static_call(pv_vcpu_is_preempted)(cpu);
> > +}
> > +
> > +int __init pv_vcpu_state_init(void);
> > +
> > #else
> >
> > +#define pv_vcpu_state_init() do {} while (0)
> > +
> > #define pv_time_init() do {} while (0)
> >
> > #endif // CONFIG_PARAVIRT
> > diff --git a/arch/arm64/kernel/paravirt.c b/arch/arm64/kernel/paravirt.c
> > index 75fed4460407..d8fc46795d94 100644
> > --- a/arch/arm64/kernel/paravirt.c
> > +++ b/arch/arm64/kernel/paravirt.c
> > @@ -40,6 +40,11 @@ struct pv_time_stolen_time_region {
> >
> > static DEFINE_PER_CPU(struct pv_time_stolen_time_region, stolen_time_region);
> >
> > +static DEFINE_PER_CPU(struct vcpu_state, vcpus_states);
>
> nit: there is only one 'state' structure per CPU, so I'd prefer the
> singular form.
ACK.
> > +struct static_key pv_vcpu_is_preempted_enabled;
> > +
> > +DEFINE_STATIC_CALL(pv_vcpu_is_preempted, dummy_vcpu_is_preempted);
> > +
> > static bool steal_acc = true;
> > static int __init parse_no_stealacc(char *arg)
> > {
> > @@ -165,3 +170,92 @@ int __init pv_time_init(void)
> >
> > return 0;
> > }
> > +
> > +bool dummy_vcpu_is_preempted(unsigned int cpu)
>
> Why does this have to be global?
I think this can be moved away from the header, so then we don't need
to DECLARE_STATIC_CALL() with a dummy function.
> > +static bool has_pv_vcpu_state(void)
> > +{
> > + struct arm_smccc_res res;
> > +
> > + /* To detect the presence of PV time support we require SMCCC 1.1+ */
> > + if (arm_smccc_1_1_get_conduit() == SMCCC_CONDUIT_NONE)
> > + return false;
> > +
> > + arm_smccc_1_1_invoke(ARM_SMCCC_ARCH_FEATURES_FUNC_ID,
> > + ARM_SMCCC_HV_PV_VCPU_STATE_FEATURES,
> > + &res);
> > +
> > + if (res.a0 != SMCCC_RET_SUCCESS)
> > + return false;
> > + return true;
>
> Please move all this over the the KVM-specific discovery mechanism.
Will take a look.
> > +static int __pv_vcpu_state_hook(unsigned int cpu, int event)
> > +{
> > + struct arm_smccc_res res;
> > + struct vcpu_state *st;
> > +
> > + st = &per_cpu(vcpus_states, cpu);
> > + arm_smccc_1_1_invoke(event, virt_to_phys(st), &res);
> > + if (res.a0 != SMCCC_RET_SUCCESS)
> > + return -EINVAL;
> > + return 0;
> > +}
> > +
> > +static int vcpu_state_init(unsigned int cpu)
> > +{
> > + int ret = __pv_vcpu_state_hook(cpu, ARM_SMCCC_HV_PV_VCPU_STATE_INIT);
> > +
> > + if (ret)
> > + pr_warn("Unable to ARM_SMCCC_HV_PV_STATE_INIT\n");
>
> pr_warn_once(), please.
ACK.
next prev parent reply other threads:[~2021-07-21 2:05 UTC|newest]
Thread overview: 25+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-07-09 4:37 [PATCHv2 0/4] arm64:kvm: teach guest sched that VCPUs can be preempted Sergey Senozhatsky
2021-07-09 4:37 ` [PATCHv2 1/4] arm64: smccc: Add SMCCC pv-vcpu-state function call IDs Sergey Senozhatsky
2021-07-12 14:22 ` Marc Zyngier
2021-07-09 4:37 ` [PATCHv2 2/4] arm64: add guest pvstate support Sergey Senozhatsky
2021-07-09 7:39 ` David Edmondson
2021-07-09 7:52 ` Sergey Senozhatsky
2021-07-09 18:58 ` Joel Fernandes
2021-07-09 21:53 ` Sergey Senozhatsky
2021-07-11 16:58 ` Joel Fernandes
2021-07-12 15:42 ` Marc Zyngier
2021-07-21 2:05 ` Sergey Senozhatsky [this message]
2021-07-21 8:22 ` Marc Zyngier
2021-07-21 8:47 ` Sergey Senozhatsky
2021-07-21 10:16 ` Marc Zyngier
2021-07-09 4:37 ` [PATCHv2 3/4] arm64: do not use dummy vcpu_is_preempted() Sergey Senozhatsky
2021-07-12 15:47 ` Marc Zyngier
2021-07-21 2:06 ` Sergey Senozhatsky
2021-07-09 4:37 ` [PATCHv2 4/4] arm64: add host pv-vcpu-state support Sergey Senozhatsky
2021-07-12 16:24 ` Marc Zyngier
2021-07-20 18:44 ` Joel Fernandes
2021-07-21 8:40 ` Marc Zyngier
2021-07-21 10:38 ` Sergey Senozhatsky
2021-07-21 11:08 ` Marc Zyngier
2021-07-21 1:15 ` Sergey Senozhatsky
2021-07-21 9:10 ` Marc Zyngier
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