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From: "Kirill A. Shutemov" <kirill@shutemov.name>
To: Dave Hansen <dave.hansen@intel.com>
Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
	tglx@linutronix.de, mingo@redhat.com, bp@alien8.de,
	luto@kernel.org, peterz@infradead.org,
	sathyanarayanan.kuppuswamy@linux.intel.com, ak@linux.intel.com,
	dan.j.williams@intel.com, david@redhat.com, hpa@zytor.com,
	seanjc@google.com, thomas.lendacky@amd.com,
	elena.reshetova@intel.com, x86@kernel.org,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH 1/2] x86/tdx: Extract GET_INFO call from get_cc_mask()
Date: Sat, 29 Oct 2022 02:59:51 +0300	[thread overview]
Message-ID: <20221028235951.p2vdu7drbbf3ccg7@box.shutemov.name> (raw)
In-Reply-To: <c97e9273-60b6-2ca7-1993-05bfbf471f3f@intel.com>

On Fri, Oct 28, 2022 at 04:27:10PM -0700, Dave Hansen wrote:
> I looked at this a bit more closely.  The code is just bonkers now.  It
> can't go in like this.
> 
> tdx_parse_tdinfo() stashes two global variables.  Then, about three
> lines later in the function, it calls get_cc_mask() which just returns
> one of those variables, modulo a little masking.
> 
> Ditto for the td_attr.  It's stashed in a global variable and then read
> one time.
> 
> There is *ZERO* reason to store 'td_attr'.  There's also zero reason to
> have 'gpa_width' as a global variable.  It's only used *ONE* *TIME* from
> the scope of *ONE* *FUNCTION*.
> 
> Even the comment is bonkers:
> 
>         /*
>          * Initializes gpa_width and td_attr. Must be called before
>          * get_cc_mask() or attribute checks.
>          */
>         tdx_parse_tdinfo();
> 
> Comments are great.  But comments that are only there because the code
> is obtuse are not.  I changed it to:
> 
>         tdx_parse_tdinfo(&cc_mask);
> 
> It doesn't even need a comment now.  Why?  Because it's obvious from the
> naming and calling convention that it initializes cc_mask and what the
> ordering dependency is.  Plus, even *if* I missed the call, or screwed
> up the order, the compiler would tell me that I'm a dolt.
> 
> The whole global variable thing actually makes the code objectively
> worse in almost every possible way.

I agree. Sorry about that.

We have more code in our tree that want to check attributes. And it is
after initialization, so the code structure derived from there.

But, yes, I should have rework it before sending upstream.

> Can you please take a look through this and make sure I didn't botch
> anything:
> 
> > https://git.kernel.org/pub/scm/linux/kernel/git/daveh/devel.git/log/?h=tdxbadve
> 
> The end result is about 50 lines less than what was there before.  Most
> of it is comment removal but the code is simpler too.
> 
> Acks and Tested-by's would be appreciated.

Looks good and works fine:

Acked-and-Tested-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>

-- 
  Kiryl Shutsemau / Kirill A. Shutemov

  reply	other threads:[~2022-10-29  0:00 UTC|newest]

Thread overview: 23+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-10-28 14:12 [PATCH 0/2] x86/tdx: Enforce no #VE on private memory accesses Kirill A. Shutemov
2022-10-28 14:12 ` [PATCH 1/2] x86/tdx: Extract GET_INFO call from get_cc_mask() Kirill A. Shutemov
2022-10-28 15:43   ` Dave Hansen
2022-10-28 23:27   ` Dave Hansen
2022-10-28 23:59     ` Kirill A. Shutemov [this message]
2022-10-31  4:12       ` Kirill A. Shutemov
2022-10-31 16:42         ` Dave Hansen
2022-10-31 19:19           ` Kirill A. Shutemov
2022-10-31 19:27         ` Andi Kleen
2022-10-31 19:44           ` Dave Hansen
2022-10-31 22:10             ` Kirill A. Shutemov
2022-10-28 14:12 ` [PATCH 2/2] x86/tdx: Do not allow #VE due to EPT violation on the private memory Kirill A. Shutemov
2022-10-28 15:41   ` Dave Hansen
2022-10-31  4:07   ` Guorui Yu
2022-10-31  4:33     ` Kirill A. Shutemov
2022-10-31 14:22     ` Dave Hansen
2022-11-04 22:36       ` Erdem Aktas
2022-11-04 22:50         ` Dave Hansen
2022-11-07 22:53           ` Erdem Aktas
2022-11-07 23:30             ` Dave Hansen
2022-11-07  5:10       ` Guorui Yu
2022-11-07 13:31         ` Dave Hansen
2022-11-07 13:43           ` Guorui Yu

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