linux-kernel - Re: [patch V2 04/16] x86/tss: Fix and move VMX BUILD_BUG

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Message-ID: <CALCETrWFyBbuxqQnnQhg0h_TkBZ666iDHiCVb6-X_yXFm-v7pQ@mail.gmail.com>
Date:   Tue, 12 Nov 2019 07:37:11 -0800
From:   Andy Lutomirski <luto@...nel.org>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     LKML <linux-kernel@...r.kernel.org>, X86 ML <x86@...nel.org>,
        Linus Torvalds <torvalds@...uxfoundation.org>,
        Andy Lutomirski <luto@...nel.org>,
        Stephen Hemminger <stephen@...workplumber.org>,
        Willy Tarreau <w@....eu>, Juergen Gross <jgross@...e.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        Paolo Bonzini <pbonzini@...hat.com>
Subject: Re: [patch V2 04/16] x86/tss: Fix and move VMX BUILD_BUG_ON()

On Mon, Nov 11, 2019 at 2:35 PM Thomas Gleixner <tglx@...utronix.de> wrote:
>
> The BUILD_BUG_ON(IO_BITMAP_OFFSET - 1 == 0x67) in the VMX code is bogus in
> two aspects:
>
> 1) This wants to be in generic x86 code simply to catch issues even when
>    VMX is disabled in Kconfig.
>
> 2) The IO_BITMAP_OFFSET is not the right thing to check because it makes
>    asssumptions about the layout of tss_struct. Nothing requires that the
>    I/O bitmap is placed right after x86_tss, which is the hardware mandated
>    tss structure. It pointlessly makes restrictions on the struct
>    tss_struct layout.
>
> The proper thing to check is:
>
>     - Offset of x86_tss in tss_struct is 0
>     - Size of x86_tss == 0x68
>
> Move it to the other build time TSS checks and make it do the right thing.
>
> Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
> Cc: Paolo Bonzini <pbonzini@...hat.com>

Acked-by: Andy Lutomirski <luto@...nel.org>