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Message-ID: <1516563099.9814.54.camel@infradead.org>
Subject: Re: [PATCH v2 5/8] x86/speculation: Add basic support for IBPB
From:   David Woodhouse <dwmw2@infradead.org>
To:     Borislav Petkov <bp@alien8.de>
Cc:     arjan@linux.intel.com, tglx@linutronix.de, karahmed@amazon.de,
        x86@kernel.org, linux-kernel@vger.kernel.org,
        tim.c.chen@linux.intel.com, peterz@infradead.org,
        pbonzini@redhat.com, ak@linux.intel.com,
        torvalds@linux-foundation.org, gregkh@linux-foundation.org
In-Reply-To: <20180121190430.ss22poeakvwzvcal@pd.tnic>
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Date:   Sun, 21 Jan 2018 19:31:39 +0000
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On Sun, 2018-01-21 at 20:04 +0100, Borislav Petkov wrote:
> On Sun, Jan 21, 2018 at 06:54:22PM +0000, David Woodhouse wrote:
> > Because we're backporting this to every stable kernel under the
> sun,
> > and they don't already require asm-goto.
>=20
> Considering the cost of the barrier, I'd simplify the whole endeavor
> *considerably* for backporting:
>=20
> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0if (boot_cpu_has(X86_FEAT=
URE_IBPB))
> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=
=C2=A0=C2=A0=C2=A0=C2=A0wrmsr(MSR_IA32_PRED_CMD, PRED_CMD_IBPB, 0);
>=20
> Problem solved.

Nope. Plenty of patch sets *did* have the bug above though, until it
was spotted.
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