linux-kernel - Re: [PATCHv3 08/11] arm64: Check for selected granule support

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Date:	Thu, 15 Oct 2015 09:47:53 -0500
From:	Jeremy Linton <jeremy.linton@....com>
To:	"Suzuki K. Poulose" <Suzuki.Poulose@....com>,
	Mark Rutland <mark.rutland@....com>
Cc:	linux-arm-kernel@...ts.infradead.org, steve.capper@...aro.org,
	ard.biesheuvel@...aro.org, marc.zyngier@....com,
	catalin.marinas@....com, will.deacon@....com,
	linux-kernel@...r.kernel.org, christoffer.dall@...aro.org
Subject: Re: [PATCHv3 08/11] arm64: Check for selected granule support

On 10/15/2015 06:25 AM, Suzuki K. Poulose wrote:
> +	/*
> +	 * Check to see if the CPU supports the requested pagesize
> +	 */
> +	asm volatile("mrs %0, ID_AA64MMFR0_EL1" : "=r" (aa64mmfr0_el1));
> +	aa64mmfr0_el1 >>= ID_AA64MMFR0_TGRAN_SHIFT;
> +	if ((aa64mmfr0_el1 & 0xf) != ID_AA64MMFR0_TGRAN_SUPPORTED) {
> +		pr_efi_err(sys_table_arg, PAGE_SIZE_STR" granule not supported by the CPU\n");
> +		return EFI_UNSUPPORTED;
> +	}

This is definitely an improvement over my original hack job.

I would like to add, that I actually think this should be in a new 
function "check_kernel_compatibility" (or whatever) that is called 
before handle_kernel_image.

That is because I don't really think it belongs in handle_kernel_image 
which is focused on relocation. Plus, if you add another function, you 
can avoid the "Failed to relocate kernel" error that comes out following 
the granule not supported message. Further, checks like this in the 
future will have a place to live.

Of course you will then need a matching stubbed out function for the 
normal arm kernel as well.

Thanks,

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