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

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Date:   Mon, 10 May 2021 15:21:51 +0200
From:   Juergen Gross <jgross@...e.com>
To:     Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        xen-devel@...ts.xenproject.org, linux-kernel@...r.kernel.org
Cc:     Stefano Stabellini <sstabellini@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH 1/3] xen: check required Xen features

On 10.05.21 14:11, Boris Ostrovsky wrote:
> 
> 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)

Depends on the use case.

XENFEAT_gnttab_map_avail_bits is relevant for driver domains using
user space backends only. In case it is not available "interesting"
things might happen.

XENFEAT_mmu_pt_update_preserve_ad not being present would result in
a subsequent mmu-update function using that feature returning -ENOSYS,
so this wouldn't be unrecognized.

So panic() might be a good idea in case the features are not available.

> (Also, chk_required_features() perhaps?)

Fine with me.


Juergen

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