linux-kernel - Re: [PATCH 4/5] efi x86: clear EFI_RUNTIME_SERVICES bit in case failures other than SetVirtualAddressMap

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Date:	Wed, 13 Aug 2014 15:27:48 +0100
From:	Matt Fleming <matt@...sole-pimps.org>
To:	Dave Young <dyoung@...hat.com>
Cc:	Matt Fleming <matt.fleming@...el.com>,
	Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will.deacon@....com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>, hpa@...or.com,
	Alessandro Zummo <a.zummo@...ertech.it>,
	Leif Lindholm <leif.lindholm@...aro.org>,
	Ard Biesheuvel <ard.biesheuvel@...aro.org>,
	Mark Salter <msalter@...hat.com>,
	Randy Dunlap <rdunlap@...radead.org>,
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	linux-efi@...r.kernel.org, rtc-linux@...glegroups.com
Subject: Re: [PATCH 4/5] efi x86: clear EFI_RUNTIME_SERVICES bit in case
 failures other than SetVirtualAddressMap

On Tue, 12 Aug, at 02:10:21PM, Dave Young wrote:
> If enter virtual mode failed due to some reason other than the efi call
> the EFI_RUNTIME_SERVICES bit in efi.flags should be cleared thus users
> of efi runtime services can check the bit and handle the case instead of
> assume efi runtime is ok.
> 
> Per Matt, if efi call SetVirtualAddressMap fails we will be not sure it's safe
> to make any assumptions about the state of the system. so kernel panics instead
> of clears EFI_RUNTIME_SERVICES bit.
> 
> Signed-off-by: Dave Young <dyoung@...hat.com>
> ---
>  arch/x86/platform/efi/efi.c | 10 ++++++++--
>  1 file changed, 8 insertions(+), 2 deletions(-)

[...]

> @@ -882,8 +886,10 @@ static void __init __efi_enter_virtual_mode(void)
>  
>  void __init efi_enter_virtual_mode(void)
>  {
> -	if (efi_enabled(EFI_PARAVIRT))
> +	if (efi_enabled(EFI_PARAVIRT)) {
> +		clear_bit(EFI_RUNTIME_SERVICES, &efi.flags);
>  		return;
> +	}

The EFI_PARAVIRT folks purposely do not set this bit, so there should be
no reason to clear it here.

-- 
Matt Fleming, Intel Open Source Technology Center
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