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

From: Boris Ostrovsky <boris.ostrovsky@oracle.com>
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>
Subject: Re: [PATCH 1/3] xen: check required Xen features
Date: Mon, 10 May 2021 08:11:56 -0400	[thread overview]
Message-ID: <4282bb6f-1d19-4d00-d468-f5d4c7fb0f90@oracle.com> (raw)
In-Reply-To: <20210422151007.2205-2-jgross@suse.com>

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);
> +	}
>  }