linux-kernel - Re: [PATCH v5 04/10] x86, efi: Reserve UEFI 2.8 Specific Purpose Memory for dax

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Date:   Fri, 13 Sep 2019 18:39:13 +0100
From:   Ard Biesheuvel <ard.biesheuvel@...aro.org>
To:     Dan Williams <dan.j.williams@...el.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        "Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
        "the arch/x86 maintainers" <x86@...nel.org>,
        Borislav Petkov <bp@...en8.de>, Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        Darren Hart <dvhart@...radead.org>,
        Andy Shevchenko <andy@...radead.org>,
        Andy Lutomirski <luto@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        kbuild test robot <lkp@...el.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Vishal L Verma <vishal.l.verma@...el.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-efi <linux-efi@...r.kernel.org>
Subject: Re: [PATCH v5 04/10] x86, efi: Reserve UEFI 2.8 Specific Purpose
 Memory for dax

On Fri, 13 Sep 2019 at 17:39, Dan Williams <dan.j.williams@...el.com> wrote:
>
> On Fri, Sep 13, 2019 at 9:29 AM Ard Biesheuvel
> <ard.biesheuvel@...aro.org> wrote:
> >
> > On Fri, 13 Sep 2019 at 17:22, Dan Williams <dan.j.williams@...el.com> wrote:
> > >
> > > On Fri, Sep 13, 2019 at 6:00 AM Ard Biesheuvel
> > > <ard.biesheuvel@...aro.org> wrote:
...
> > > > > diff --git a/drivers/firmware/efi/efi.c b/drivers/firmware/efi/efi.c
> > > > > index 363bb9d00fa5..6d54d5c74347 100644
> > > > > --- a/drivers/firmware/efi/efi.c
> > > > > +++ b/drivers/firmware/efi/efi.c
> > > > > @@ -52,6 +52,9 @@ struct efi __read_mostly efi = {
> > > > >         .tpm_log                = EFI_INVALID_TABLE_ADDR,
> > > > >         .tpm_final_log          = EFI_INVALID_TABLE_ADDR,
> > > > >         .mem_reserve            = EFI_INVALID_TABLE_ADDR,
> > > > > +#ifdef CONFIG_EFI_SOFT_RESERVE
> > > > > +       .flags                  = 1UL << EFI_MEM_SOFT_RESERVE,
> > > > > +#endif
> > > > >  };
> > > > >  EXPORT_SYMBOL(efi);
> > > > >
> > > >
> > > > I'd prefer it if we could call this EFI_MEM_NO_SOFT_RESERVE instead,
> > > > and invert the meaning of the bit.
> > >
> > > ...but that would mean repeat occurrences of
> > > "!efi_enabled(EFI_MEM_NO_SOFT_RESERVE)", doesn't the double negative
> > > seem less readable to you?
> > >
> >
> > One the one hand, yes. On the other hand, it is the only flag whose
> > default is 'enabled' which is also less than ideal.
>
> Ok, I can get on board with "default 0" being the non exception state
> of the flags.
>

In fact, let's just add something like

static inline bool efi_soft_reserve_enabled(void)
{
    return IS_ENABLED(CONFIG_EFI_SOFT_RESERVE) &&
           !efi_enabled(EFI_MEM_NO_SOFT_RESERVE);
}

to linux/efi.h and use that in the code?