Re: [PATCH v7 07/12] xen: enable Dom0 to use SVE feature

[Jan Beulich <jbeulich@xxxxxxxx>]

On 23.05.2023 09:43, Luca Fancellu wrote:
> Add a command line parameter to allow Dom0 the use of SVE resources,
> the command line parameter sve=<integer>, sub argument of dom0=,
> controls the feature on this domain and sets the maximum SVE vector
> length for Dom0.
> 
> Add a new function, parse_signed_integer(), to parse an integer
> command line argument.
> 
> Signed-off-by: Luca Fancellu <luca.fancellu@xxxxxxx>

Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx> # !arm

> --- a/docs/misc/xen-command-line.pandoc
> +++ b/docs/misc/xen-command-line.pandoc
> @@ -777,9 +777,9 @@ Specify the bit width of the DMA heap.
>  
>  ### dom0
>      = List of [ pv | pvh, shadow=<bool>, verbose=<bool>,
> -                cpuid-faulting=<bool>, msr-relaxed=<bool> ]
> +                cpuid-faulting=<bool>, msr-relaxed=<bool> ] (x86)
>  
> -    Applicability: x86
> +    = List of [ sve=<integer> ] (Arm)

While in the text below you mention this is Arm64 only, I think the tag
here would better express this as well.

> @@ -838,6 +838,22 @@ Controls for how dom0 is constructed on x86 systems.
>  
>      If using this option is necessary to fix an issue, please report a bug.
>  
> +Enables features on dom0 on Arm systems.
> +
> +*   The `sve` integer parameter enables Arm SVE usage for Dom0 domain and 
> sets
> +    the maximum SVE vector length, the option is applicable only to AArch64
> +    guests.

Why "guests"? Does the option affect more than Dom0?

> +    A value equal to 0 disables the feature, this is the default value.
> +    Values below 0 means the feature uses the maximum SVE vector length
> +    supported by hardware, if SVE is supported.
> +    Values above 0 explicitly set the maximum SVE vector length for Dom0,
> +    allowed values are from 128 to maximum 2048, being multiple of 128.
> +    Please note that when the user explicitly specifies the value, if that 
> value
> +    is above the hardware supported maximum SVE vector length, the domain
> +    creation will fail and the system will stop, the same will occur if the
> +    option is provided with a non zero value, but the platform doesn't 
> support
> +    SVE.

Assuming this also covers the -1 case, I wonder if that isn't a little too
strict. "Maximum supported" imo can very well be 0.

Jan