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From: "Jürgen Groß" <jgross@suse.com>
To: Marc Zyngier <maz@kernel.org>, Steven Price <steven.price@arm.com>
Cc: kvm@vger.kernel.org, Catalin Marinas <catalin.marinas@arm.com>,
	linux-doc@vger.kernel.org, Russell King <linux@armlinux.org.uk>,
	linux-kernel@vger.kernel.org, Paolo Bonzini <pbonzini@redhat.com>,
	Will Deacon <will@kernel.org>,
	kvmarm@lists.cs.columbia.edu,
	linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH v6 10/10] arm64: Retrieve stolen time as paravirtualized guest
Date: Mon, 21 Oct 2019 07:01:21 +0200
Message-ID: <237a3457-bcb3-c9b7-11ef-241b7ccc370e@suse.com> (raw)
In-Reply-To: <86a79wzdhk.wl-maz@kernel.org>

On 19.10.19 22:28, Marc Zyngier wrote:
> On Fri, 11 Oct 2019 13:59:30 +0100,
> Steven Price <steven.price@arm.com> wrote:
>>
>> Enable paravirtualization features when running under a hypervisor
>> supporting the PV_TIME_ST hypercall.
>>
>> For each (v)CPU, we ask the hypervisor for the location of a shared
>> page which the hypervisor will use to report stolen time to us. We set
>> pv_time_ops to the stolen time function which simply reads the stolen
>> value from the shared page for a VCPU. We guarantee single-copy
>> atomicity using READ_ONCE which means we can also read the stolen
>> time for another VCPU than the currently running one while it is
>> potentially being updated by the hypervisor.
>>
>> Signed-off-by: Steven Price <steven.price@arm.com>
>> ---
>>   .../admin-guide/kernel-parameters.txt         |   6 +-
>>   arch/arm64/include/asm/paravirt.h             |   9 +-
>>   arch/arm64/kernel/paravirt.c                  | 148 ++++++++++++++++++
>>   arch/arm64/kernel/time.c                      |   3 +
>>   include/linux/cpuhotplug.h                    |   1 +
>>   5 files changed, 163 insertions(+), 4 deletions(-)
>>
>> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
>> index c7ac2f3ac99f..346b1c7a4afb 100644
>> --- a/Documentation/admin-guide/kernel-parameters.txt
>> +++ b/Documentation/admin-guide/kernel-parameters.txt
>> @@ -3083,9 +3083,9 @@
>>   			[X86,PV_OPS] Disable paravirtualized VMware scheduler
>>   			clock and use the default one.
>>   
>> -	no-steal-acc	[X86,KVM] Disable paravirtualized steal time accounting.
>> -			steal time is computed, but won't influence scheduler
>> -			behaviour
>> +	no-steal-acc	[X86,KVM,ARM64] Disable paravirtualized steal time
>> +			accounting. steal time is computed, but won't
>> +			influence scheduler behaviour
>>   
>>   	nolapic		[X86-32,APIC] Do not enable or use the local APIC.
>>   
>> diff --git a/arch/arm64/include/asm/paravirt.h b/arch/arm64/include/asm/paravirt.h
>> index 799d9dd6f7cc..125c26c42902 100644
>> --- a/arch/arm64/include/asm/paravirt.h
>> +++ b/arch/arm64/include/asm/paravirt.h
>> @@ -21,6 +21,13 @@ static inline u64 paravirt_steal_clock(int cpu)
>>   {
>>   	return pv_ops.time.steal_clock(cpu);
>>   }
>> -#endif
>> +
>> +int __init kvm_guest_init(void);
>> +
>> +#else
>> +
>> +#define kvm_guest_init()
>> +
>> +#endif // CONFIG_PARAVIRT
>>   
>>   #endif
>> diff --git a/arch/arm64/kernel/paravirt.c b/arch/arm64/kernel/paravirt.c
>> index 4cfed91fe256..de73dbec238c 100644
>> --- a/arch/arm64/kernel/paravirt.c
>> +++ b/arch/arm64/kernel/paravirt.c
>> @@ -6,13 +6,161 @@
>>    * Author: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
>>    */
>>   
>> +#define pr_fmt(fmt) "kvmarm-pv: " fmt
>> +
>> +#include <linux/arm-smccc.h>
>> +#include <linux/cpuhotplug.h>
>>   #include <linux/export.h>
>> +#include <linux/io.h>
>>   #include <linux/jump_label.h>
>> +#include <linux/printk.h>
>> +#include <linux/psci.h>
>> +#include <linux/reboot.h>
>> +#include <linux/slab.h>
>>   #include <linux/types.h>
>> +
>>   #include <asm/paravirt.h>
>> +#include <asm/pvclock-abi.h>
>> +#include <asm/smp_plat.h>
>>   
>>   struct static_key paravirt_steal_enabled;
>>   struct static_key paravirt_steal_rq_enabled;
>>   
>>   struct paravirt_patch_template pv_ops;
>>   EXPORT_SYMBOL_GPL(pv_ops);
>> +
>> +struct kvmarm_stolen_time_region {
>> +	struct pvclock_vcpu_stolen_time *kaddr;
>> +};
>> +
>> +static DEFINE_PER_CPU(struct kvmarm_stolen_time_region, stolen_time_region);
>> +
>> +static bool steal_acc = true;
>> +static int __init parse_no_stealacc(char *arg)
>> +{
>> +	steal_acc = false;
>> +	return 0;
>> +}
>> +
>> +early_param("no-steal-acc", parse_no_stealacc);
>> +
>> +/* return stolen time in ns by asking the hypervisor */
>> +static u64 kvm_steal_clock(int cpu)
> 
> This isn't KVM specific.
> 
>> +{
>> +	struct kvmarm_stolen_time_region *reg;
>> +
>> +	reg = per_cpu_ptr(&stolen_time_region, cpu);
>> +	if (!reg->kaddr) {
>> +		pr_warn_once("stolen time enabled but not configured for cpu %d\n",
>> +			     cpu);
>> +		return 0;
>> +	}
>> +
>> +	return le64_to_cpu(READ_ONCE(reg->kaddr->stolen_time));
>> +}
>> +
>> +static int disable_stolen_time_current_cpu(void)
>> +{
>> +	struct kvmarm_stolen_time_region *reg;
>> +
>> +	reg = this_cpu_ptr(&stolen_time_region);
>> +	if (!reg->kaddr)
>> +		return 0;
>> +
>> +	memunmap(reg->kaddr);
>> +	memset(reg, 0, sizeof(*reg));
>> +
>> +	return 0;
>> +}
>> +
>> +static int stolen_time_dying_cpu(unsigned int cpu)
>> +{
>> +	return disable_stolen_time_current_cpu();
>> +}
> 
> You can merge these two functions, as there is no other caller.
> 
>> +
>> +static int init_stolen_time_cpu(unsigned int cpu)
>> +{
>> +	struct kvmarm_stolen_time_region *reg;
>> +	struct arm_smccc_res res;
>> +
>> +	reg = this_cpu_ptr(&stolen_time_region);
>> +
>> +	arm_smccc_1_1_invoke(ARM_SMCCC_HV_PV_TIME_ST, &res);
>> +
>> +	if ((long)res.a0 < 0)
>> +		return -EINVAL;
> 
> I'd rather you check an actual error code, just in case the memory map
> starts growing to a point where we have 64bit (I)PAs...
> 
>> +
>> +	reg->kaddr = memremap(res.a0,
>> +			      sizeof(struct pvclock_vcpu_stolen_time),
>> +			      MEMREMAP_WB);
>> +
>> +	if (!reg->kaddr) {
>> +		pr_warn("Failed to map stolen time data structure\n");
>> +		return -ENOMEM;
>> +	}
>> +
>> +	if (le32_to_cpu(reg->kaddr->revision) != 0 ||
>> +	    le32_to_cpu(reg->kaddr->attributes) != 0) {
>> +		pr_warn("Unexpected revision or attributes in stolen time data\n");
> 
> WARN_ONCE instead? You probably don't want to scream for each and
> every CPU that boots...
> 
>> +		return -ENXIO;
>> +	}
>> +
>> +	return 0;
>> +}
>> +
>> +static int kvm_arm_init_stolen_time(void)
>> +{
>> +	int ret;
>> +
>> +	ret = cpuhp_setup_state(CPUHP_AP_ARM_KVMPV_STARTING,
>> +				"hypervisor/kvmarm/pv:starting",
>> +				init_stolen_time_cpu, stolen_time_dying_cpu);
>> +	if (ret < 0)
>> +		return ret;
>> +	return 0;
>> +}
>> +
>> +static bool has_kvm_steal_clock(void)
> 
> This is not KVM specific either.
> 
>> +{
>> +	struct arm_smccc_res res;
>> +
>> +	/* To detect the presence of PV time support we require SMCCC 1.1+ */
>> +	if (psci_ops.smccc_version < SMCCC_VERSION_1_1)
>> +		return false;
>> +
>> +	arm_smccc_1_1_invoke(ARM_SMCCC_ARCH_FEATURES_FUNC_ID,
>> +			     ARM_SMCCC_HV_PV_TIME_FEATURES, &res);
>> +
>> +	if (res.a0 != SMCCC_RET_SUCCESS)
>> +		return false;
>> +
>> +	arm_smccc_1_1_invoke(ARM_SMCCC_HV_PV_TIME_FEATURES,
>> +			     ARM_SMCCC_HV_PV_TIME_ST, &res);
>> +
>> +	if (res.a0 != SMCCC_RET_SUCCESS)
>> +		return false;
>> +
>> +	return true;
> 
> 	return (res.a0 == SMCCC_RET_SUCCESS);
> 
>> +}
>> +
>> +int __init kvm_guest_init(void)
> 
> How about something like pv_time_init() instead? In the guest, this is
> no way KVM specific, and I still hope for this to work on things like
> Xen/HyperV/VMware (yeah, I'm foolishly optimistic). All the references
> to KVM should go, and be replaced by something more generic (after
> all, you're only implementing the spec, so feel free to call it
> den0057_* if you really want).

Xen guests already have the needed functionality. On ARM this just needs
to be hooked up.


Juergen
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Thread overview: 24+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-10-11 12:59 [PATCH v6 00/10] arm64: Stolen time support Steven Price
2019-10-11 12:59 ` [PATCH v6 01/10] KVM: arm64: Document PV-time interface Steven Price
2019-10-11 12:59 ` [PATCH v6 02/10] KVM: arm/arm64: Factor out hypercall handling from PSCI code Steven Price
2019-10-11 12:59 ` [PATCH v6 03/10] KVM: arm64: Implement PV_TIME_FEATURES call Steven Price
2019-10-11 12:59 ` [PATCH v6 04/10] KVM: Implement kvm_put_guest() Steven Price
2019-10-11 12:59 ` [PATCH v6 05/10] KVM: arm64: Support stolen time reporting via shared structure Steven Price
2019-10-19 11:12   ` Marc Zyngier
2019-10-21 10:21     ` Steven Price
2019-10-21 10:40       ` Marc Zyngier
2019-10-21 11:24         ` Steven Price
2019-10-11 12:59 ` [PATCH v6 06/10] KVM: Allow kvm_device_ops to be const Steven Price
2019-10-11 12:59 ` [PATCH v6 07/10] KVM: arm64: Provide VCPU attributes for stolen time Steven Price
2019-10-19 11:28   ` Marc Zyngier
2019-10-21 11:00     ` Steven Price
2019-10-11 12:59 ` [PATCH v6 08/10] arm/arm64: Provide a wrapper for SMCCC 1.1 calls Steven Price
2019-10-21 11:42   ` Marc Zyngier
2019-10-21 13:43     ` Steven Price
2019-10-21 14:05       ` Marc Zyngier
2019-10-11 12:59 ` [PATCH v6 09/10] arm/arm64: Make use of the SMCCC 1.1 wrapper Steven Price
2019-10-11 12:59 ` [PATCH v6 10/10] arm64: Retrieve stolen time as paravirtualized guest Steven Price
2019-10-19 20:28   ` Marc Zyngier
2019-10-21  5:01     ` Jürgen Groß [this message]
2019-10-21  7:55       ` Marc Zyngier
2019-10-21 12:14     ` Steven Price

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