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From:   Linus Torvalds <torvalds@linux-foundation.org>
Date:   Tue, 27 Jun 2023 13:26:18 -0700
Message-ID: <CAHk-=wi9Uwo3-uwB4rT=wK2VKhGq3yEp_U-b2kruogCT=13Mjg@mail.gmail.com>
Subject: Re: [GIT PULL] x86/misc for 6.5
To:     Borislav Petkov <bp@alien8.de>,
        Noah Goldstein <goldstein.w.n@gmail.com>,
        Dave Hansen <dave.hansen@linux.intel.com>
Cc:     x86-ml <x86@kernel.org>, lkml <linux-kernel@vger.kernel.org>
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On Tue, 27 Jun 2023 at 13:11, Linus Torvalds
<torvalds@linux-foundation.org> wrote:
>
> Finally: did I already mention that this is completely untested?

Oh, this part is buggy:

+               asm("addq %1,%0\n\t"
+                   "adcq $0,%0"
+                   :"=r" (temp64): "r" (temp64_2));

and it needs to show that 'temp64' is an input too.

Dummy me.

The trivial fix is just to make the "=r" be a "+r".

In fact, I should have used "+r" inside update_csum_40b(), but at
least there I did add the proper input constraint, so that one isn't
actively buggy.

And again: I noticed this by looking at the patch one more time. No
actual *testing* has happened. It might still be buggy garbage even
with that "+r". It's just a bit *less* buggy garbage.

I will now go back to my cave and continue pulling stuff, I just had
to do something else for a while. Some people relax with a nice drink
by the pool, I relax by playing around with inline asm.

                Linus