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From: Michael Kelley <mikelley@microsoft.com>
To: Mark Rutland <Mark.Rutland@arm.com>
Cc: "will@kernel.org" <will@kernel.org>,
	"catalin.marinas@arm.com" <catalin.marinas@arm.com>,
	"lorenzo.pieralisi@arm.com" <lorenzo.pieralisi@arm.com>,
	"sudeep.holla@arm.com" <sudeep.holla@arm.com>,
	"linux-arm-kernel@lists.infradead.org"
	<linux-arm-kernel@lists.infradead.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"linux-hyperv@vger.kernel.org" <linux-hyperv@vger.kernel.org>,
	"linux-efi@vger.kernel.org" <linux-efi@vger.kernel.org>,
	"arnd@arndb.de" <arnd@arndb.de>,
	"wei.liu@kernel.org" <wei.liu@kernel.org>,
	"ardb@kernel.org" <ardb@kernel.org>,
	"daniel.lezcano@linaro.org" <daniel.lezcano@linaro.org>,
	KY Srinivasan <kys@microsoft.com>
Subject: RE: [PATCH v10 3/7] arm64: hyperv: Add Hyper-V clocksource/clockevent support
Date: Fri, 14 May 2021 15:35:15 +0000	[thread overview]
Message-ID: <MWHPR21MB15932B44EC1E55614B219F5ED7509@MWHPR21MB1593.namprd21.prod.outlook.com> (raw)
In-Reply-To: <20210514123711.GB30645@C02TD0UTHF1T.local>

From: Mark Rutland <mark.rutland@arm.com> Sent: Friday, May 14, 2021 5:37 AM
> 
> Hi Michael,
> 
> On Wed, May 12, 2021 at 10:37:43AM -0700, Michael Kelley wrote:
> > Add architecture specific definitions and functions needed
> > by the architecture independent Hyper-V clocksource driver.
> > Update the Hyper-V clocksource driver to be initialized
> > on ARM64.
> 
> Previously we've said that for a clocksource we must use the architected
> counter, since that's necessary for things like the VDSO to work
> correctly and efficiently.
> 
> Given that, I'm a bit confused that we're registering a per-cpu
> clocksource that is in part based on the architected counter. Likewise,
> I don't entirely follow why it's necessary to PV the clock_event_device.
> 
> Are the architected counter and timer reliable without this PV
> infrastructure? Why do we need to PV either of those?
> 
> Thanks,
> Mark.
> 

For the clocksource, we have a requirement to live migrate VMs
between Hyper-V hosts running on hardware that may have different
arch counter frequencies (it's not conformant to the ARM v8.6 1 GHz
requirement).  The Hyper-V virtualization does scaling to handle the
frequency difference.  And yes, there's a tradeoff with vDSO not
working, though we have an out-of-tree vDSO implementation that
we can use when necessary.

For clockevents, the only timer interrupt that Hyper-V provides
in a guest VM is its virtualized "STIMER" interrupt.  There's no
virtualization of the ARM arch timer in the guest.

Michael

> >
> > Signed-off-by: Michael Kelley <mikelley@microsoft.com>
> > Reviewed-by: Sunil Muthuswamy <sunilmut@microsoft.com>
> > ---
> >  arch/arm64/include/asm/mshyperv.h  | 12 ++++++++++++
> >  drivers/clocksource/hyperv_timer.c | 14 ++++++++++++++
> >  2 files changed, 26 insertions(+)
> >
> > diff --git a/arch/arm64/include/asm/mshyperv.h b/arch/arm64/include/asm/mshyperv.h
> > index c448704..b17299c 100644
> > --- a/arch/arm64/include/asm/mshyperv.h
> > +++ b/arch/arm64/include/asm/mshyperv.h
> > @@ -21,6 +21,7 @@
> >  #include <linux/types.h>
> >  #include <linux/arm-smccc.h>
> >  #include <asm/hyperv-tlfs.h>
> > +#include <clocksource/arm_arch_timer.h>
> >
> >  /*
> >   * Declare calls to get and set Hyper-V VP register values on ARM64, which
> > @@ -41,6 +42,17 @@ static inline u64 hv_get_register(unsigned int reg)
> >  	return hv_get_vpreg(reg);
> >  }
> >
> > +/* Define the interrupt ID used by STIMER0 Direct Mode interrupts. This
> > + * value can't come from ACPI tables because it is needed before the
> > + * Linux ACPI subsystem is initialized.
> > + */
> > +#define HYPERV_STIMER0_VECTOR	31
> > +
> > +static inline u64 hv_get_raw_timer(void)
> > +{
> > +	return arch_timer_read_counter();
> > +}
> > +
> >  /* SMCCC hypercall parameters */
> >  #define HV_SMCCC_FUNC_NUMBER	1
> >  #define HV_FUNC_ID	ARM_SMCCC_CALL_VAL(			\
> > diff --git a/drivers/clocksource/hyperv_timer.c b/drivers/clocksource/hyperv_timer.c
> > index 977fd05..270ad9c 100644
> > --- a/drivers/clocksource/hyperv_timer.c
> > +++ b/drivers/clocksource/hyperv_timer.c
> > @@ -569,3 +569,17 @@ void __init hv_init_clocksource(void)
> >  	hv_setup_sched_clock(read_hv_sched_clock_msr);
> >  }
> >  EXPORT_SYMBOL_GPL(hv_init_clocksource);
> > +
> > +/* Initialize everything on ARM64 */
> > +static int __init hyperv_timer_init(struct acpi_table_header *table)
> > +{
> > +	if (!hv_is_hyperv_initialized())
> > +		return -EINVAL;
> > +
> > +	hv_init_clocksource();
> > +	if (hv_stimer_alloc(true))
> > +		return -EINVAL;
> > +
> > +	return 0;
> > +}
> > +TIMER_ACPI_DECLARE(hyperv, ACPI_SIG_GTDT, hyperv_timer_init);
> > --
> > 1.8.3.1
> >

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  reply	other threads:[~2021-05-14 15:37 UTC|newest]

Thread overview: 26+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-05-12 17:37 [PATCH v10 0/7] Enable Linux guests on Hyper-V on ARM64 Michael Kelley
2021-05-12 17:37 ` [PATCH v10 1/7] asm-generic: hyperv: Fix incorrect architecture dependencies Michael Kelley
2021-05-12 17:37 ` [PATCH v10 2/7] arm64: hyperv: Add Hyper-V hypercall and register access utilities Michael Kelley
2021-05-14 12:52   ` Mark Rutland
2021-05-14 15:14     ` Michael Kelley
2021-05-17 11:44       ` Mark Rutland
2021-05-17 16:41         ` Michael Kelley
2021-05-12 17:37 ` [PATCH v10 3/7] arm64: hyperv: Add Hyper-V clocksource/clockevent support Michael Kelley
2021-05-14 12:37   ` Mark Rutland
2021-05-14 15:35     ` Michael Kelley [this message]
2021-05-17 13:08       ` Mark Rutland
2021-05-17 17:27         ` Michael Kelley
2021-05-18 17:00           ` Mark Rutland
2021-06-08 15:36             ` Michael Kelley
2021-06-10 16:45               ` Mark Rutland
2021-06-14  2:42                 ` Michael Kelley
2021-06-16 20:17                   ` Michael Kelley
2021-06-22  9:54                   ` Mark Rutland
2021-06-23  8:56                     ` Marc Zyngier
2021-06-28  2:21                       ` Michael Kelley
2021-05-12 17:37 ` [PATCH v10 4/7] arm64: hyperv: Add kexec and panic handlers Michael Kelley
2021-05-12 17:37 ` [PATCH v10 5/7] arm64: hyperv: Initialize hypervisor on boot Michael Kelley
2021-05-13 15:16   ` Wei Liu
2021-05-12 17:37 ` [PATCH v10 6/7] arm64: efi: Export screen_info Michael Kelley
2021-05-12 17:37 ` [PATCH v10 7/7] Drivers: hv: Enable Hyper-V code to be built on ARM64 Michael Kelley
2021-05-13 13:17 ` [PATCH v10 0/7] Enable Linux guests on Hyper-V " Sudeep Holla

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