Re: [PATCH 1/3] xen: check required Xen features

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

On Thu, 22 Apr 2021, Juergen Gross wrote:
> Linux kernel is not supported to run on Xen versions older than 4.0.
> 
> Add tests for required Xen features always being present in Xen 4.0
> and newer.
> 
> Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
> ---
>  drivers/xen/features.c | 18 ++++++++++++++++++
>  1 file changed, 18 insertions(+)
> 
> diff --git a/drivers/xen/features.c b/drivers/xen/features.c
> index 25c053b09605..60503299c9bc 100644
> --- a/drivers/xen/features.c
> +++ b/drivers/xen/features.c
> @@ -9,13 +9,26 @@
>  #include <linux/types.h>
>  #include <linux/cache.h>
>  #include <linux/export.h>
> +#include <linux/printk.h>
>  
>  #include <asm/xen/hypercall.h>
>  
> +#include <xen/xen.h>
>  #include <xen/interface/xen.h>
>  #include <xen/interface/version.h>
>  #include <xen/features.h>
>  
> +/*
> + * Linux kernel expects at least Xen 4.0.
> + *
> + * Assume some features to be available for that reason (depending on guest
> + * mode, of course).
> + */
> +#define chk_feature(f) {                                             \
> +             if (!xen_feature(f))                                    \
> +                     pr_err("Xen: feature %s not available!\n", #f); \
> +     }

I think this could be done as a static inline function in
include/xen/features.h. That way it would be available everywhere. Also,
static inlines are better than macro when it is possible to use them in
terms of code safety.


>  u8 xen_features[XENFEAT_NR_SUBMAPS * 32] __read_mostly;
>  EXPORT_SYMBOL_GPL(xen_features);
>  
> @@ -31,4 +44,9 @@ void xen_setup_features(void)
>               for (j = 0; j < 32; j++)
>                       xen_features[i * 32 + j] = !!(fi.submap & 1<<j);
>       }
> +
> +     if (xen_pv_domain()) {
> +             chk_feature(XENFEAT_mmu_pt_update_preserve_ad);
> +             chk_feature(XENFEAT_gnttab_map_avail_bits);
> +     }
>  }
> -- 
> 2.26.2
>