linux-kernel - Re: [PATCH 1/1] x86/platform/x86: Fix count of CHas on multi-pci-segment arches

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Message-ID: <CAHp75VcgF11Y5RHFriu+fcuyzRdtGzcVWX5OK5yfOwhoKXS+Eg@mail.gmail.com>
Date:   Tue, 13 Mar 2018 19:46:49 +0200
From:   Andy Shevchenko <andy.shevchenko@...il.com>
To:     "Liang, Kan" <kan.liang@...ux.intel.com>
Cc:     "Kroening, Gary" <gary.kroening@....com>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "hpa@...or.com" <hpa@...or.com>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "peterz@...radead.org" <peterz@...radead.org>,
        "Travis, Mike" <mike.travis@....com>,
        "Banman, Andrew" <abanman@....com>,
        "Sivanich, Dimitri" <dimitri.sivanich@....com>,
        "Anderson, Russ" <russ.anderson@....com>,
        "x86@...nel.org" <x86@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/1] x86/platform/x86: Fix count of CHas on
 multi-pci-segment arches

>>>> +       pci_read_config_dword(dev, SKX_CAPID6, &val);
>>>> +       return bitmap_weight((unsigned long *)&val, SKX_CHA_BIT_WIDTH);
>>>
>>>
>>> UB is here.
>>> Fix is simple, use unsigned long and drop this ugly casting.
>>>
>
> Just noticed that we have to do casting anyway.

No.

> pci_read_config_dword uses u32.
> bitmap_weight uses unsigned long.

...which would lead to UB.

So,

unsigned long bits;
u32 value;

...(..., &value);
bits = value;
...(&bits, ...);

-- 
With Best Regards,
Andy Shevchenko