linux-kernel - Re: [PATCH v4 10/10] arm64: Retrieve stolen time as paravirtualized guest

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Date:   Wed, 4 Sep 2019 17:01:11 +0100
From:   Steven Price <steven.price@....com>
To:     Andrew Jones <drjones@...hat.com>
Cc:     Marc Zyngier <maz@...nel.org>, Will Deacon <will@...nel.org>,
        linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.cs.columbia.edu,
        Catalin Marinas <catalin.marinas@....com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Radim Krčmář <rkrcmar@...hat.com>,
        Russell King <linux@...linux.org.uk>,
        James Morse <james.morse@....com>,
        Julien Thierry <julien.thierry.kdev@...il.com>,
        Suzuki K Pouloze <suzuki.poulose@....com>,
        Mark Rutland <mark.rutland@....com>, kvm@...r.kernel.org,
        linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 10/10] arm64: Retrieve stolen time as paravirtualized
 guest

On 03/09/2019 09:47, Andrew Jones wrote:
> On Fri, Aug 30, 2019 at 09:42:55AM +0100, Steven Price 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@....com>
>> ---
>>  arch/arm64/include/asm/paravirt.h |   9 +-
>>  arch/arm64/kernel/paravirt.c      | 148 ++++++++++++++++++++++++++++++
>>  arch/arm64/kernel/time.c          |   3 +
>>  include/linux/cpuhotplug.h        |   1 +
>>  4 files changed, 160 insertions(+), 1 deletion(-)
>>
>> 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..5bf3be7ccf7e 100644
>> --- a/arch/arm64/kernel/paravirt.c
>> +++ b/arch/arm64/kernel/paravirt.c
>> @@ -6,13 +6,161 @@
>>   * Author: Stefano Stabellini <stefano.stabellini@...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);
> 
> Need to also add an 'ARM64' to the
> Documentation/admin-guide/kernel-parameters.txt entry for this.

Good point, thanks for the pointer.

Steve