linux-kernel - Re: [PATCH 2/2] efi/esrt: mark ESRT memory region as nomap

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Date:   Sat, 24 Feb 2018 15:22:57 +0800
From:   Dave Young <dyoung@...hat.com>
To:     Tyler Baicar <tbaicar@...eaurora.org>
Cc:     ard.biesheuvel@...aro.org, linux-efi@...r.kernel.org,
        linux-kernel@...r.kernel.org, jhugo@...eaurora.org,
        sgoel@...eaurora.org, takahiro.akashi@...aro.org,
        timur@...eaurora.org
Subject: Re: [PATCH 2/2] efi/esrt: mark ESRT memory region as nomap

On 02/23/18 at 12:42pm, Tyler Baicar wrote:
> The ESRT memory region is being exposed as System RAM in /proc/iomem
> which is wrong because it cannot be overwritten. This memory is needed
> for kexec kernels in order to properly initialize ESRT, so if it is
> overwritten it will cause ESRT failures in the kexec kernel. Mark this
> region as nomap so that it is not overwritten.
> 
> Signed-off-by: Tyler Baicar <tbaicar@...eaurora.org>
> Tested-by: Jeffrey Hugo <jhugo@...eaurora.org>
> ---
>  drivers/firmware/efi/esrt.c | 8 ++++++++
>  1 file changed, 8 insertions(+)
> 
> diff --git a/drivers/firmware/efi/esrt.c b/drivers/firmware/efi/esrt.c
> index 504f3c3..f5f79c7 100644
> --- a/drivers/firmware/efi/esrt.c
> +++ b/drivers/firmware/efi/esrt.c
> @@ -335,6 +335,14 @@ void __init efi_esrt_init(void)
>  	pr_info("Reserving ESRT space from %pa to %pa.\n", &esrt_data, &end);
>  	efi_mem_reserve(esrt_data, esrt_data_size);
>  
> +	/*
> +	 * Mark the ESRT memory region as nomap to avoid it being exposed as
> +	 * System RAM in /proc/iomem. Otherwise this block can be overwritten
> +	 * which will then cause failures in kexec'd kernels since the ESRT
> +	 * information is no longer there.
> +	 */
> +	memblock_mark_nomap(esrt_data, esrt_data_size);
> +

On my X86 machine, esrt region was marked as reserved /proc/iomem,
this issue could be a arm64 only problem, it is better to handle this in
arm init code.


>  	pr_debug("esrt-init: loaded.\n");
>  err_memunmap:
>  	early_memunmap(va, size);
> -- 
> Qualcomm Datacenter Technologies, Inc. as an affiliate of Qualcomm Technologies, Inc.
> Qualcomm Technologies, Inc. is a member of the Code Aurora Forum,
> a Linux Foundation Collaborative Project.
> 
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Thanks
Dave