linux-kernel - Re: [PATCH 3/6] efi/libstub: Introduce ExitBootServices helper

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Message-ID: <20160822164100.GB11327@gmail.com>
Date:   Mon, 22 Aug 2016 18:41:00 +0200
From:   Ingo Molnar <mingo@...nel.org>
To:     Matt Fleming <matt@...eblueprint.co.uk>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        "H . Peter Anvin" <hpa@...or.com>,
        Jeffrey Hugo <jhugo@...eaurora.org>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        linux-kernel@...r.kernel.org, linux-efi@...r.kernel.org,
        Leif Lindholm <leif.lindholm@...aro.org>,
        Mark Rutland <mark.rutland@....com>, stable@...r.kernel.org
Subject: Re: [PATCH 3/6] efi/libstub: Introduce ExitBootServices helper


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

> From: Jeffrey Hugo <jhugo@...eaurora.org>
> 
> The spec allows ExitBootServices to fail with EFI_INVALID_PARAMETER if a
> race condition has occurred where the EFI has updated the memory map after
> the stub grabbed a reference to the map.  The spec defines a retry
> proceedure with specific requirements to handle this scenario.
> 
> This scenario was previously observed on x86 - commit d3768d885c6c ("x86,
> efi: retry ExitBootServices() on failure") but the current fix is not spec
> compliant and the scenario is now observed on the Qualcomm Technologies
> QDF2432 via the FDT stub which does not handle the error and thus causes
> boot failures.

It's unclear what this 'scenario' is. How does the user notice?

> Add a helper to the stub library that correctly adhears to the spec in the
> case of EFI_INVALID_PARAMETER from ExitBootServices and can be universally
> used across all stub implementations.

s/'adheres to'

> +		status = efi_call_early(exit_boot_services, handle,
> +					*map->key_ptr);

Please don't add spurious linebreaks in such a case - just keep it a bit longer 
than col80.

> +	if (status != EFI_SUCCESS)
> +		/* exit_boot_services() was called, thus cannot free*/
> +		goto fail;

Non-standard comment format and comment placement.

Thanks,

	Ingo