linux-kernel - Re: [PATCH v2 03/15] mshyperv: Introduce numa_node_to_proximity_domain

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Message-ID: <51095880-da66-5041-e47c-6572f199f6db@intel.com>
Date:   Thu, 17 Aug 2023 17:26:21 -0700
From:   Dave Hansen <dave.hansen@...el.com>
To:     Nuno Das Neves <nunodasneves@...ux.microsoft.com>,
        linux-hyperv@...r.kernel.org, linux-kernel@...r.kernel.org,
        x86@...nel.org, linux-arm-kernel@...ts.infradead.org,
        linux-arch@...r.kernel.org
Cc:     patches@...ts.linux.dev, mikelley@...rosoft.com, kys@...rosoft.com,
        wei.liu@...nel.org, haiyangz@...rosoft.com, decui@...rosoft.com,
        apais@...ux.microsoft.com, Tianyu.Lan@...rosoft.com,
        ssengar@...ux.microsoft.com, mukeshrathor@...rosoft.com,
        stanislav.kinsburskiy@...il.com, jinankjain@...ux.microsoft.com,
        vkuznets@...hat.com, tglx@...utronix.de, mingo@...hat.com,
        bp@...en8.de, dave.hansen@...ux.intel.com, hpa@...or.com,
        will@...nel.org, catalin.marinas@....com
Subject: Re: [PATCH v2 03/15] mshyperv: Introduce
 numa_node_to_proximity_domain_info

On 8/17/23 17:17, Nuno Das Neves wrote:
>>> +	if (node != NUMA_NO_NODE) {
>>> +		proximity_domain_info.domain_id = node_to_pxm(node);
>>> +		proximity_domain_info.flags.reserved = 0;
>>> +		proximity_domain_info.flags.proximity_info_valid = 1;
>>> +		proximity_domain_info.flags.proximity_preferred = 1;
>>> +	} else {
>>> +		proximity_domain_info.as_uint64 = 0;
>>> +	}
>>> +
>>> +	return proximity_domain_info;
>>> +}
>> Pop quiz: What are the rules for the 30 bits of uninitialized data of
>> proximity_domain_info.flags in the (node != NUMA_NO_NODE) case?
>>
>> I actually don't know off the top of my head.  I generally avoid
>> bitfields, but if they were normal stack-allocated variable space,
>> they'd be garbage.
> I'm not sure what you are getting at here - all the fields are
> initialized.

Whoops, I somehow missed the reserved field initialization.  But, yeah,
a struct would be nice instead of the union here.