Re: [Xen-devel] [PATCH v4 15/15] docs: Describe PVHv2's VCPU hotplug procedure

[Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>]

On Tue, Nov 29, 2016 at 10:33:22AM -0500, Boris Ostrovsky wrote:
> Signed-off-by: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>

Reviewed-by: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>

> ---
> CC: George Dunlap <George.Dunlap@xxxxxxxxxxxxx>
> CC: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
> CC: Stefano Stabellini <sstabellini@xxxxxxxxxx>
> CC: Tim Deegan <tim@xxxxxxx>
> ---
> Changes in v4:
> * Updated text to reflect new interfaces.
> 
>  docs/misc/hvmlite.markdown | 13 +++++++++++++
>  1 file changed, 13 insertions(+)
> 
> diff --git a/docs/misc/hvmlite.markdown b/docs/misc/hvmlite.markdown
> index 898b8ee..71c6bc2 100644
> --- a/docs/misc/hvmlite.markdown
> +++ b/docs/misc/hvmlite.markdown
> @@ -75,3 +75,16 @@ info structure that's passed at boot time (field 
> rsdp_paddr).
>  
>  Description of paravirtualized devices will come from XenStore, just as it's
>  done for HVM guests.
> +
> +## VCPU hotplug ##
> +
> +VCPU hotplug (e.g. 'xl vcpu-set <domain> <num_vcpus>') for PVHv2 guests
> +follows ACPI model where change in domain's number of VCPUS (stored in
> +domain.avail_vcpus) results in an SCI being sent to the guest. The guest
> +then executes DSDT's PRSC method, updating MADT enable status for the
> +affected VCPU.
> +
> +This is achieved by having the toolstack issue a write to ACPI's
> +XEN_ACPI_CPU_MAP (thus updating the VCPU available map stored there),
> +followed by a write to ACPI GPE0 status register, setting XEN_GPE0_CPUHP_BIT.
> +The latter will cause an SCI to be generated.
> -- 
> 2.7.4
> 

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