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Subject: Re: [PATCH 1/3] xen: check required Xen features
To:     Juergen Gross <jgross@suse.com>, xen-devel@lists.xenproject.org,
        linux-kernel@vger.kernel.org
Cc:     Stefano Stabellini <sstabellini@kernel.org>,
        Peter Zijlstra <peterz@infradead.org>
References: <20210422151007.2205-1-jgross@suse.com>
 <20210422151007.2205-2-jgross@suse.com>
From:   Boris Ostrovsky <boris.ostrovsky@oracle.com>
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Date:   Mon, 10 May 2021 08:11:56 -0400
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On 4/22/21 11:10 AM, Juergen Gross wrote:
>  
> +/*
> + * 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);	\
> +	}


With your changes in the subsequent patches, are we still going to function properly without those features? (i.e. maybe we should just panic)


(Also, chk_required_features() perhaps?)


-boris


> +
>  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);
> +	}
>  }