linux-kernel - Re: [PATCH] x86/platform/UV: Fix support for EFI_OLD

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Message-ID: <20161019125626.GA6249@gmail.com>
Date:   Wed, 19 Oct 2016 14:56:26 +0200
From:   Ingo Molnar <mingo@...nel.org>
To:     Matt Fleming <matt@...eblueprint.co.uk>
Cc:     Alex Thorlton <athorlton@....com>, linux-kernel@...r.kernel.org,
        Mike Travis <travis@....com>, Russ Anderson <rja@....com>,
        Dimitri Sivanich <sivanich@....com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        Masahiro Yamada <yamada.masahiro@...ionext.com>,
        x86@...nel.org, Ard Biesheuvel <ard.biesheuvel@...aro.org>
Subject: Re: [PATCH] x86/platform/UV: Fix support for EFI_OLD_MEMMAP after
 BIOS callback updates


* Matt Fleming <matt@...eblueprint.co.uk> wrote:

> On Tue, 18 Oct, at 07:47:38AM, Alex Thorlton wrote:
> > Some time ago, we brought our UV BIOS callback code up to speed with the
> > new EFI memory mapping scheme, in commit:
> > 
> >     d1be84a232e3 ("x86/uv: Update uv_bios_call() to use efi_call_virt_pointer()")
> > 
> > By leveraging some changes that I made to a few of the EFI runtime
> > callback mechanisms, in commit:
> > 
> >     80e75596079f ("efi: Convert efi_call_virt() to efi_call_virt_pointer()")
> > 
> > This got everything running smoothly on UV, with the new EFI mapping
> > code.  However, this left one, small loose end, in that EFI_OLD_MEMMAP
> > (a.k.a. efi=old_map) will no longer work on UV, on kernels that include
> > the aforementioned changes.
> > 
> > At the time this was not a major issue (in fact, it still really isn't),
> > but there's no reason that EFI_OLD_MEMMAP *shouldn't* work on our
> > systems.  This commit adds a check into uv_bios_call, to see if we have
> > the EFI_OLD_MEMMAP bit set in efi.flags.  If it is set, we fall back to
> > using our old callback method, which uses efi_call directly on the __va
> > of our function pointer.
> > 
> > Signed-off-by: Alex Thorlton <athorlton@....com>
> > Cc: Mike Travis <travis@....com>
> > Cc: Russ Anderson <rja@....com>
> > Cc: Dimitri Sivanich <sivanich@....com>
> > Cc: Thomas Gleixner <tglx@...utronix.de>
> > Cc: Ingo Molnar <mingo@...hat.com>
> > Cc: "H. Peter Anvin" <hpa@...or.com>
> > Cc: Matt Fleming <matt@...eblueprint.co.uk>
> > Cc: Masahiro Yamada <yamada.masahiro@...ionext.com>
> > Cc: x86@...nel.org
> > ---
> >  arch/x86/platform/uv/bios_uv.c | 10 +++++++++-
> >  1 file changed, 9 insertions(+), 1 deletion(-)
> > 
> > diff --git a/arch/x86/platform/uv/bios_uv.c b/arch/x86/platform/uv/bios_uv.c
> > index b4d5e95..12b6e52 100644
> > --- a/arch/x86/platform/uv/bios_uv.c
> > +++ b/arch/x86/platform/uv/bios_uv.c
> > @@ -40,7 +40,15 @@ s64 uv_bios_call(enum uv_bios_cmd which, u64 a1, u64 a2, u64 a3, u64 a4, u64 a5)
> >  		 */
> >  		return BIOS_STATUS_UNIMPLEMENTED;
> >  
> > -	ret = efi_call_virt_pointer(tab, function, (u64)which, a1, a2, a3, a4, a5);
> > +	/*
> > +	 * If EFI_OLD_MEMMAP is set, we need to fall back to using our old EFI
> > +	 * callback method, which uses efi_call directly, with the kernel page tables.
> > +	 */
> > +	if (!test_bit(EFI_OLD_MEMMAP, &efi.flags))
> > +		ret = efi_call_virt_pointer(tab, function, (u64)which, a1, a2, a3, a4, a5);
> > +	else
> > +		ret = efi_call((void *)__va(tab->function), (u64)which, a1, a2, a3, a4, a5);
> > +
> >  	return ret;
> >  }
> >  EXPORT_SYMBOL_GPL(uv_bios_call);
> 
> Could you please invert the conditional? I had to read it 3 times to
> make sure it was correct given the comment that precedes it. E.g. this
> is preferable,
> 
> 	if (efi_enabled(EFI_OLD_MEMMAP))
> 		ret = efi_call((void *)__va(tab->function), (u64)which, a1, a2, a3, a4, a5);
> 	else
> 		ret = efi_call_virt_pointer(tab, function, (u64)which, a1, a2, a3, a4, a5);

Also, does 'which' have to be explicitly type-cast to u64? Doesn't the compiler DTRT?

Thanks,

	Ingo