linux-kernel - Re: [PATCHv3 02/11] arm64: Handle section maps for swapper/idmap

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Date:	Wed, 14 Oct 2015 16:08:43 +0100
From:	"Suzuki K. Poulose" <Suzuki.Poulose@....com>
To:	Mark Rutland <mark.rutland@....com>
Cc:	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	catalin.marinas@....com, will.deacon@....com,
	steve.capper@...aro.org, marc.zyngier@....com,
	ard.biesheuvel@...aro.org, christoffer.dall@...aro.org
Subject: Re: [PATCHv3 02/11] arm64: Handle section maps for swapper/idmap

On 14/10/15 15:51, Mark Rutland wrote:
>>>> +/* With 4K pages, we use section maps. */

>> /*
>>   * ARM64 kernel is guaranteed to be loaded at 2M aligned
>>   * address (as per booting requirements). Hence we can use
>>   * section mapping with 4K (section size = 2M) and not with
>>   * 16K(section size = 32M) or 64K (section size = 512M).
>>   */
>
> That sounds much better. I hadn't figured out why myself, so thanks for
> the explanation :)
>
> However, there's one minor nit: the start of memory below the kernel is
> 2M aligned, but the offset means that the kernel itself is not loaded at
> a 2M aligned address.

Oh yes

>
> So how about:
>
> /*
>   * The linear mapping and the start of memory are both 2M aligned (per
>   * the arm64 booting.txt requirements). Hence we can use section mapping
>   * with 4K (section size = 2M) but not with 16K (section size = 32M) or
>   * 64K (section size = 512M).
>   */

Will add this

Thanks
Suzuki

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