linux-kernel - Re: [PATCH V2 3/4] xen/unpopulated-alloc: Add mechanism to use Xen resource

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Message-ID: <00a9467a-3e48-9c68-1ac2-7ec2c7380d97@gmail.com>
Date:   Tue, 9 Nov 2021 20:51:54 +0200
From:   Oleksandr <olekstysh@...il.com>
To:     Boris Ostrovsky <boris.ostrovsky@...cle.com>
Cc:     xen-devel@...ts.xenproject.org, linux-kernel@...r.kernel.org,
        Oleksandr Tyshchenko <oleksandr_tyshchenko@...m.com>,
        Juergen Gross <jgross@...e.com>,
        Stefano Stabellini <sstabellini@...nel.org>,
        Julien Grall <julien@....org>
Subject: Re: [PATCH V2 3/4] xen/unpopulated-alloc: Add mechanism to use Xen
 resource


On 28.10.21 22:08, Boris Ostrovsky wrote:

Hi Boris

I am sorry for the late response.

>
> On 10/26/21 12:05 PM, Oleksandr Tyshchenko wrote:
>>   +static void unpopulated_init(void)
>> +{
>> +    static bool inited = false;
>> +    int ret;
>> +
>> +    if (inited)
>> +        return;
>> +
>> +    /*
>> +     * Try to initialize Xen resource the first and fall back to 
>> default
>> +     * resource if arch doesn't offer one.
>> +     */
>> +    ret = arch_xen_unpopulated_init(&xen_resource);
>> +    if (!ret)
>> +        target_resource = &xen_resource;
>> +    else if (ret == -ENOSYS)
>> +        target_resource = &iomem_resource;
>> +    else
>> +        pr_err("Cannot initialize Xen resource\n");
>
>
> I'd pass target_resource as a parameter to arch_xen_unpopulated_init() 
> instead. Default routine will assign it iomem_resource and you won't 
> have to deal with -ENOSYS.

That would be much better, thank you. Will do.


>
>
>
> Also, what happens in case of error? Is it fatal? I don't think your 
> changes in fill_list() will work.

The error is fatal as we don't have a suitable resource to allocate a 
region from, and yes, the fill_list() must not be called.


>
>
>
>> +
>> +    inited = true;
>
>
> I agree with Stefano in that it would be better to call this from an 
> init function, and you won't have t worry about multiple calls here.

Yes, that's good point, thank you. Will do.


>
>
>
> -boris

-- 
Regards,

Oleksandr Tyshchenko