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
Subject: Re: [PATCH v2 5/8] x86/speculation: Add basic support for IBPB
Date: Sun, 21 Jan 2018 20:07:06 +0000 [thread overview]
Message-ID: <1516565226.9814.63.camel@infradead.org> (raw)
In-Reply-To: <20180121195407.hbahkbmc37yrrvi4@pd.tnic>
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On Sun, 2018-01-21 at 20:54 +0100, Borislav Petkov wrote:
> On Sun, Jan 21, 2018 at 07:31:39PM +0000, David Woodhouse wrote:
> > > if (boot_cpu_has(X86_FEATURE_IBPB))
> > > wrmsr(MSR_IA32_PRED_CMD, PRED_CMD_IBPB, 0);
> > >
> > > Problem solved.
> >
> > Nope. Plenty of patch sets *did* have the bug above though, until it
> > was spotted.
>
> And that bug is...?
That bug is the *reason* we're arguing about static_cpu_has vs.
ALTERNATIVE.
A conditional branch that the CPU sees can be speculated over...
Now, Andrew is right that in a number of cases there will be another
serialising instruction before we ever hit a problematic indirect
branch. But as I just said elsewhere, I'd really like the *primitives*
to support unconditional operation.
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next prev parent reply other threads:[~2018-01-21 20:07 UTC|newest]
Thread overview: 35+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-01-21 9:49 [PATCH v2 0/8] Speculation Control feature support, IBPB David Woodhouse
2018-01-21 9:49 ` [PATCH v2 1/8] x86/cpufeatures: Add Intel feature bits for Speculation Control David Woodhouse
2018-01-21 10:17 ` Ingo Molnar
2018-01-21 9:49 ` [PATCH v2 2/8] x86/cpufeatures: Add AMD feature bits for Prediction Command David Woodhouse
2018-01-21 17:50 ` Tom Lendacky
2018-01-21 18:01 ` Andrew Cooper
2018-01-22 14:31 ` Tom Lendacky
2018-01-22 14:33 ` Andrew Cooper
2018-01-21 9:49 ` [PATCH v2 3/8] x86/msr: Add definitions for new speculation control MSRs David Woodhouse
2018-01-21 13:06 ` Jiri Slaby
2018-01-21 13:27 ` David Woodhouse
2018-01-21 9:49 ` [PATCH v2 4/8] x86/pti: Do not enable PTI on fixed Intel processors David Woodhouse
2018-01-21 13:38 ` Borislav Petkov
2018-01-21 9:49 ` [PATCH v2 5/8] x86/speculation: Add basic support for IBPB David Woodhouse
2018-01-21 10:26 ` Ingo Molnar
2018-01-21 18:06 ` Borislav Petkov
2018-01-21 18:29 ` KarimAllah Ahmed
2018-01-21 19:01 ` Borislav Petkov
2018-01-21 19:31 ` David Woodhouse
2018-01-21 19:37 ` Andrew Cooper
2018-01-21 20:04 ` David Woodhouse
2018-01-21 20:19 ` Andrew Cooper
2018-01-21 21:25 ` David Woodhouse
2018-01-21 19:53 ` Borislav Petkov
2018-01-21 18:54 ` David Woodhouse
2018-01-21 19:04 ` Borislav Petkov
2018-01-21 19:31 ` David Woodhouse
2018-01-21 19:54 ` Borislav Petkov
2018-01-21 20:07 ` David Woodhouse [this message]
2018-01-21 20:17 ` Borislav Petkov
2018-01-21 9:49 ` [PATCH v2 6/8] x86/kvm: Add IBPB support David Woodhouse
2018-01-21 18:06 ` Tom Lendacky
2018-01-21 9:49 ` [PATCH v2 7/8] x86/speculation: Use Indirect Branch Prediction Barrier in context switch David Woodhouse
2018-01-21 9:49 ` [PATCH v2 8/8] x86/mm: Only flush indirect branches when switching into non dumpable process David Woodhouse
2018-01-21 10:33 ` Ingo Molnar
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