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Date: Wed, 28 Jul 2021 14:17:27 +0100
From: Christoph Hellwig <hch@infradead.org>
To: Tom Lendacky <thomas.lendacky@amd.com>
Subject: Re: [PATCH 01/11] mm: Introduce a function to check for
 virtualization protection features
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On Tue, Jul 27, 2021 at 05:26:04PM -0500, Tom Lendacky via iommu wrote:
> In prep for other protected virtualization technologies, introduce a
> generic helper function, prot_guest_has(), that can be used to check
> for specific protection attributes, like memory encryption. This is
> intended to eliminate having to add multiple technology-specific checks
> to the code (e.g. if (sev_active() || tdx_active())).

So common checks obviously make sense, but I really hate the stupid
multiplexer.  Having one well-documented helper per feature is much
easier to follow.

> +#define PATTR_MEM_ENCRYPT		0	/* Encrypted memory */
> +#define PATTR_HOST_MEM_ENCRYPT		1	/* Host encrypted memory */
> +#define PATTR_GUEST_MEM_ENCRYPT		2	/* Guest encrypted memory */
> +#define PATTR_GUEST_PROT_STATE		3	/* Guest encrypted state */

The kerneldoc comments on these individual helpers will give you plenty
of space to properly document what they indicate and what a (potential)
caller should do based on them.  Something the above comments completely
fail to.