Re: [Xen-devel] [PATCH 0/2] Support consistent reads of mapped vcpu_runstate_info

[Juergen Gross <jgross@xxxxxxxx>]

On 20/05/16 16:10, Julien Grall wrote:
> Hi Juergen,
> 
> On 20/05/16 14:22, Juergen Gross wrote:
>> A guest mapping vcpu_runstate_info into its memory can't read this
>> information from another cpu but the one the data is referring to.
>> Reason is there is no reliable way for the guest to detect a concurrent
>> data update by the hypervisor.
>>
>> This patch series adds an update flag to the mapped data which can be
>> used by the guest to detect an update is occurring. As this flag is
>> modifying the current interface it has to be activated by using a
>> vm_assist hypercall, which in turn has to be made available for ARM.
>>
>> Runtime tested on x86 with a modified Linux kernel using the new
>> feature.
>> Compile tested only for ARM.
> 
> I would like to give a go on ARM. Who it be possible to provide the
> patch for Linux and how to test it?

Sure. You'll need the four attached patches (to be applied on top of
kernel 4.6). With CONFIG_PARAVIRT_TIME_ACCOUNTING set in the kernel
config, full functionality will be used (without being set the runstate
info of other cpus won't be read).

You can verify the vm_assist hypercall has worked via "xl debug-keys q"
and "xl dmesg | grep vm_assist" (value should be 00000020 on ARM).


Juergen

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