linux-kernel - Re: [PATCH v2 4/7] platform/x86/intel/ifs: Implement Array BIST test

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Message-ID: <e2cd922a-0a5e-c1ef-3fe7-2347f3b062d1@intel.com>
Date:   Wed, 15 Feb 2023 09:44:39 -0800
From:   "Joseph, Jithu" <jithu.joseph@...el.com>
To:     Dave Hansen <dave.hansen@...el.com>, <hdegoede@...hat.com>,
        <markgross@...nel.org>
CC:     <tglx@...utronix.de>, <mingo@...hat.com>, <bp@...en8.de>,
        <dave.hansen@...ux.intel.com>, <x86@...nel.org>, <hpa@...or.com>,
        <gregkh@...uxfoundation.org>, <rostedt@...dmis.org>,
        <ashok.raj@...el.com>, <tony.luck@...el.com>,
        <linux-kernel@...r.kernel.org>,
        <platform-driver-x86@...r.kernel.org>, <patches@...ts.linux.dev>,
        <ravi.v.shankar@...el.com>, <thiago.macieira@...el.com>,
        <athenas.jimenez.gonzalez@...el.com>, <sohil.mehta@...el.com>
Subject: Re: [PATCH v2 4/7] platform/x86/intel/ifs: Implement Array BIST test



On 2/15/2023 8:58 AM, Dave Hansen wrote:
> On 2/14/23 15:44, Jithu Joseph wrote:
...
> 
>> +static void ifs_array_test_core(int cpu, struct device *dev)
>> +{
>> +	union ifs_array activate, status = {0};
> 
> So, 'status' here is initialized to 0.  But, 'activate'... hmmm
> 
> Here's 1 of the 4 fields getting initialized:
> 
>> +	activate.array_bitmask = ~0U;
>> +	timeout = jiffies + HZ / 2;
>> +
>> +	do {
>> +		if (time_after(jiffies, timeout)) {
>> +			timed_out = true;
>> +			break;
>> +		}
>> +
>> +		msrvals[0] = activate.data;
> 
> and then the *WHOLE* union is read here.  What *is* the uninitialized
> member behavior of a bitfield?  I actually haven't the foggiest idea
> since I never use them.  Is there some subtly C voodoo that initializes
> the other 3 fields?

Thanks for pointing the mistake Dave. I see the bug w.r.t not initializing activate to
zero.

Thanks Dave for the proposed patch . Let me get back after taking a detailed look

Jithu