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: <e7113e249fa0fc1f259408c9f97655ec199dba5e.camel@xry111.site>
Subject: Re: A question about prefetchw detection in "x86/asm: Cleanup
 prefetch primitives"
From:   Xi Ruoyao <xry111@xry111.site>
To:     Borislav Petkov <bp@alien8.de>
Cc:     x86@kernel.org, linux-kernel@vger.kernel.org,
        Thomas Gleixner <tglx@linutronix.de>
Date:   Wed, 21 Jun 2023 21:47:36 +0800
In-Reply-To: <20230621134645.GIZJL/Rf1IdeLMQGl2@fat_crate.local>
References: <0b663d8f6802e8dbf443397718234bcb6d0811c8.camel@xry111.site>
         <20230621111346.GFZJLbavDw1JiLi34n@fat_crate.local>
         <a155ebb791d3aefce5db32658e3c519a1cfac1f6.camel@xry111.site>
         <e76180a1b82d1c29715587e94e2d6923b64bb893.camel@xry111.site>
         <20230621125749.GGZJLzzUw0rA3goV1X@fat_crate.local>
         <b50735128c5a985634468d63fef092f093f0aebc.camel@xry111.site>
         <20230621130955.GHZJL2o771lIEPURUl@fat_crate.local>
         <29beee7faf370ea892cb4e5a85ddd1f7ee132164.camel@xry111.site>
         <20230621134645.GIZJL/Rf1IdeLMQGl2@fat_crate.local>
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable
User-Agent: Evolution 3.48.3 
MIME-Version: 1.0
Precedence: bulk

On Wed, 2023-06-21 at 15:46 +0200, Borislav Petkov wrote:
> On Wed, Jun 21, 2023 at 09:19:34PM +0800, Xi Ruoyao wrote:
> > On Wed, 2023-06-21 at 15:09 +0200, Borislav Petkov wrote:
> > > On Wed, Jun 21, 2023 at 09:06:51PM +0800, Xi Ruoyao wrote:
> > > > I think it's not an issue in the kernel itself, but announcing
> > > > 3dnowprefetch in /proc/cpuinfo for an old Intel CPU w/o real
> > > > prefetchw
> > > > implementation seems problematic (to me).
> > >=20
> > > And this is a problem because?
> >=20
> > If a code generator parses /proc/cpuinfo for CPU capabilities, it
> > may
> > generates a no-op prefetchw instead of prefetcht0 as a fallback.
>=20
> Err, go back.
>=20
> That code snippet you pasted, did you see where that comes from?
>=20
> A function called init_amd().
>=20
> Now, is Intel hardware and SDM PREFETCHW text at all relevant here?

Oh s**t, I'm completely stupid :(.

--=20
Xi Ruoyao <xry111@xry111.site>
School of Aerospace Science and Technology, Xidian University