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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>
Cc:     linux-kernel@vger.kernel.org, x86@kernel.org,
        linuxppc-dev@lists.ozlabs.org, linux-s390@vger.kernel.org,
        iommu@lists.linux-foundation.org, kvm@vger.kernel.org,
        linux-efi@vger.kernel.org, platform-driver-x86@vger.kernel.org,
        linux-graphics-maintainer@vmware.com,
        amd-gfx@lists.freedesktop.org, dri-devel@lists.freedesktop.org,
        kexec@lists.infradead.org, linux-fsdevel@vger.kernel.org,
        Andi Kleen <ak@linux.intel.com>,
        Tianyu Lan <Tianyu.Lan@microsoft.com>,
        Borislav Petkov <bp@alien8.de>,
        Brijesh Singh <brijesh.singh@amd.com>
Subject: Re: [PATCH 01/11] mm: Introduce a function to check for
 virtualization protection features
Message-ID: <YQFY5/cq2thyHzUe@infradead.org>
References: <cover.1627424773.git.thomas.lendacky@amd.com>
 <cbc875b1d2113225c2b44a2384d5b303d0453cf7.1627424774.git.thomas.lendacky@amd.com>
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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.