Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
Message-ID: <052d7b15-1b3f-490e-fb30-538334b67a0a@intel.com>
Date:   Thu, 24 Feb 2022 09:01:42 -0800
MIME-Version: 1.0
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101
 Thunderbird/91.5.0
Content-Language: en-US
To:     "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
        tglx@linutronix.de, mingo@redhat.com, bp@alien8.de,
        luto@kernel.org, peterz@infradead.org
Cc:     sathyanarayanan.kuppuswamy@linux.intel.com, aarcange@redhat.com,
        ak@linux.intel.com, dan.j.williams@intel.com, david@redhat.com,
        hpa@zytor.com, jgross@suse.com, jmattson@google.com,
        joro@8bytes.org, jpoimboe@redhat.com, knsathya@kernel.org,
        pbonzini@redhat.com, sdeep@vmware.com, seanjc@google.com,
        tony.luck@intel.com, vkuznets@redhat.com, wanpengli@tencent.com,
        thomas.lendacky@amd.com, brijesh.singh@amd.com, x86@kernel.org,
        linux-kernel@vger.kernel.org
References: <20220224155630.52734-1-kirill.shutemov@linux.intel.com>
 <20220224155630.52734-5-kirill.shutemov@linux.intel.com>
From:   Dave Hansen <dave.hansen@intel.com>
Subject: Re: [PATCHv4 04/30] x86/tdx: Add __tdx_module_call() and
 __tdx_hypercall() helper functions
In-Reply-To: <20220224155630.52734-5-kirill.shutemov@linux.intel.com>
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 7bit
Precedence: bulk

On 2/24/22 07:56, Kirill A. Shutemov wrote:
> +	tdcall
> +
> +	/*
> +	 * TDVMCALL leaf does not suppose to fail. If it fails something
> +	 * is horribly wrong with TDX module. Stop the world.
> +	 */
> +	testq %rax, %rax
> +	jne .Lpanic

This should be:

	"A TDVMCALL is not supposed to fail."

I also wish this was mentioning something about the difference between a
failure and return code.

	/*
	 * %rax==0 indicates a failure of the TDVMCALL mechanism itself
	 * and that something has gone horribly wrong with the TDX
	 * module.
	 *
	 * The return status of the hypercall operation is separate
	 * (in %r10).  Hypercall errors are a part of normal operation
	 * and are handled by callers.
	 */

I've been confused by this exact thing multiple times over the months
that I've been looking at this code.  I think it deserves a good comment.