Re: [PATCH v7 09/12] xen: add runtime parameter access support to hypfs

[Jan Beulich <jbeulich@xxxxxxxx>]

On 02.04.2020 17:46, Juergen Gross wrote:
> V7:
> - fine tune some parameter initializations (Jan Beulich)
> - call custom_runtime_set_var() after updating the value
> - modify alignment in Arm linker script to 4 (Jan Beulich)

I didn't ask for this to be unilaterally 4 - I don't think this
would work on Arm64, seeing that there are pointers inside the
struct. This wants to be pointer size, i.e. 4 for Arm32 but 8
for Arm64.

> --- a/docs/misc/hypfs-paths.pandoc
> +++ b/docs/misc/hypfs-paths.pandoc
> @@ -152,3 +152,12 @@ The major version of Xen.
>  #### /buildinfo/version/minor = INTEGER
>  
>  The minor version of Xen.
> +
> +#### /params/
> +
> +A directory of runtime parameters.
> +
> +#### /params/*
> +
> +The individual parameters. The description of the different parameters can be
> +found in `docs/misc/xen-command-line.pandoc`.

Is .pandoc a useful specification here, or do such extensions get
converted when rendering into different formats?

> --- a/xen/arch/x86/hvm/vmx/vmcs.c
> +++ b/xen/arch/x86/hvm/vmx/vmcs.c
> @@ -70,6 +70,30 @@ integer_param("ple_window", ple_window);
>  static bool __read_mostly opt_ept_pml = true;
>  static s8 __read_mostly opt_ept_ad = -1;
>  int8_t __read_mostly opt_ept_exec_sp = -1;
> +static char opt_ept_setting[24];
> +
> +static void update_ept_param_append(const char *str, int val)
> +{
> +    char *pos = opt_ept_setting + strlen(opt_ept_setting);
> +
> +    snprintf(pos, sizeof(opt_ept_setting) - (pos - opt_ept_setting),
> +             ",%s=%d", str, val);
> +}
> +
> +static void update_ept_param(void)
> +{
> +    snprintf(opt_ept_setting, sizeof(opt_ept_setting), "pml=%d", 
> opt_ept_pml);
> +    if ( opt_ept_ad >= 0 )
> +        update_ept_param_append("ad", opt_ept_ad);

With the new patch 1, is the if() here really still needed? Then
again, only "exec-sp" is a runtime sub-parameter anyway afaict,
and hence I'd expect only that part of the option should be
displayed (I'm sorry for not having paid attention to this
earlier).

Jan