linux-kernel - Re: [PATCH v4 01/17] x86/common: Align cpu_caps_cleared and cpu_caps

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Message-ID: <d1f6f2f1-60c9-9dc8-0ad5-14cf94e83487@redhat.com>
Date:   Mon, 4 Mar 2019 11:48:18 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Fenghua Yu <fenghua.yu@...el.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        H Peter Anvin <hpa@...or.com>,
        Dave Hansen <dave.hansen@...el.com>,
        Ashok Raj <ashok.raj@...el.com>,
        Ravi V Shankar <ravi.v.shankar@...el.com>,
        Xiaoyao Li <xiaoyao.li@...el.com>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        x86 <x86@...nel.org>, kvm@...r.kernel.org
Subject: Re: [PATCH v4 01/17] x86/common: Align cpu_caps_cleared and
 cpu_caps_set to unsigned long

On 04/03/19 11:17, Peter Zijlstra wrote:
> On Mon, Mar 04, 2019 at 09:33:16AM +0100, Paolo Bonzini wrote:
>> Why not instead change set_bit/clear_bit to use btsl/btrl instead of
>> btsq/btrq?
> 
> At least one of the faulty users (wireless) is in generic code and needs
> fixing regardless.
> 
> For better or worse; the bitmap stuff is defined to work on unsigned
> long. Using it on smaller types already relies on small endian; but
> further enabling just makes it worse I feel. Better have the rules be
> uniform.

True that.  On the other hand btsl/btrl is also one byte smaller if no 
operand is %r8-%r15.

In any case, /me wonders if we should have a macro like

#define DECLARE_LE_BITMAP(name,bits) \
        u32 name[DIV_ROUND_UP(bits, 32)] __aligned(sizeof(unsigned long))

Paolo