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

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Message-ID: <20161019113200.GE31476@codeblueprint.co.uk>
Date:   Wed, 19 Oct 2016 12:32:00 +0100
From:   Matt Fleming <matt@...eblueprint.co.uk>
To:     Alex Thorlton <athorlton@....com>
Cc:     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

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);