From: "Woodhouse, David" <dwmw@amazon.co.uk>
To: Andrew Cooper <andrew.cooper3@citrix.com>,
Andi Kleen <ak@linux.intel.com>,
Tom Lendacky <thomas.lendacky@amd.com>
Cc: Paul Turner <pjt@google.com>, LKML <linux-kernel@vger.kernel.org>,
"Linus Torvalds" <torvalds@linux-foundation.org>,
Greg Kroah-Hartman <gregkh@linux-foundation.org>,
Tim Chen <tim.c.chen@linux.intel.com>,
"Dave Hansen" <dave.hansen@intel.com>, <tglx@linutronix.de>,
Kees Cook <keescook@google.com>, Rik van Riel <riel@redhat.com>,
Peter Zijlstra <peterz@infradead.org>,
Andy Lutomirski <luto@amacapital.net>,
Jiri Kosina <jikos@kernel.org>, <gnomes@lxorguk.ukuu.org.uk>,
Thomas Lendacky <Thomas.Lendacky@amd.com>
Subject: Re: [PATCH v5 02/12] x86/retpoline: Add initial retpoline support
Date: Sat, 6 Jan 2018 21:21:20 +0000 [thread overview]
Message-ID: <1515273680.29312.272.camel@amazon.co.uk> (raw)
In-Reply-To: <0c150bb9-f5eb-2bf2-1f64-84c1b315868b@citrix.com>
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On Sat, 2018-01-06 at 21:16 +0000, Andrew Cooper wrote:
> On 06/01/18 11:49, David Woodhouse wrote:
> > diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
> > index 372ba3f..40e6e54 100644
> > --- a/arch/x86/kernel/cpu/common.c
> > +++ b/arch/x86/kernel/cpu/common.c
> > @@ -904,6 +904,11 @@ static void __init early_identify_cpu(struct cpuinfo_x86 *c)
> >
> > setup_force_cpu_bug(X86_BUG_SPECTRE_V1);
> > setup_force_cpu_bug(X86_BUG_SPECTRE_V2);
> > +#ifdef CONFIG_RETPOLINE
> > + setup_force_cpu_cap(X86_FEATURE_RETPOLINE);
> > + if (c->x86_vendor == X86_VENDOR_AMD)
> > + setup_force_cpu_cap(X86_FEATURE_RETPOLINE_AMD);
>
> This isn't safe. It needs to be dependant on finding that LFENCEs are
> actually dispatch serialising.
>
> In particular, when virtualised, you'll most likely be saddled with the
> hypervisors choice of setting, in which case you need to use retpoline
> as a fallback.
Thanks. I was about to rebase on top of tip/x86/pti which has Tom's
patches to make lfence serialising — which seem to say that if the MSR
isn't available, it *will* be serialising.
I think I'll just refrain from setting X86_FEATURE_RETPOLINE_AMD for
now, and let Tom turn that on in his own time.
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next prev parent reply other threads:[~2018-01-06 21:22 UTC|newest]
Thread overview: 36+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-01-06 11:49 [PATCH v5 00/12] Retpoline: Avoid speculative indirect calls in kernel David Woodhouse
2018-01-06 11:49 ` [PATCH v5 01/12] x86/spectre: Add X86_BUG_SPECTRE_V[12] David Woodhouse
2018-01-06 21:05 ` [tip:x86/pti] x86/cpufeatures: " tip-bot for David Woodhouse
2018-01-06 11:49 ` [PATCH v5 02/12] x86/retpoline: Add initial retpoline support David Woodhouse
2018-01-06 17:32 ` David Woodhouse
2018-01-06 18:05 ` [PATCH v5.1 " David Woodhouse
2018-01-06 18:35 ` [PATCH v5 " Eric Biggers
2018-01-06 19:17 ` David Woodhouse
2018-01-06 21:16 ` Andrew Cooper
2018-01-06 21:21 ` Woodhouse, David [this message]
2018-01-07 1:44 ` Tom Lendacky
2018-01-06 21:23 ` Thomas Gleixner
2018-01-06 21:34 ` Andrew Cooper
2018-01-06 21:49 ` Woodhouse, David
2018-01-06 11:49 ` [PATCH v5 03/12] x86/retpoline/crypto: Convert crypto assembler indirect jumps David Woodhouse
2018-01-06 11:49 ` [PATCH v5 04/12] x86/retpoline/entry: Convert entry " David Woodhouse
2018-01-06 11:49 ` [PATCH v5 05/12] x86/retpoline/ftrace: Convert ftrace " David Woodhouse
2018-01-06 18:13 ` Linus Torvalds
2018-01-06 19:53 ` Thomas Gleixner
2018-01-07 1:27 ` Linus Torvalds
2018-01-06 11:49 ` [PATCH v5 06/12] x86/retpoline/hyperv: Convert " David Woodhouse
2018-01-06 11:49 ` [PATCH v5 07/12] x86/retpoline/xen: Convert Xen hypercall " David Woodhouse
2018-01-06 11:49 ` [PATCH v5 08/12] x86/retpoline/checksum32: Convert assembler " David Woodhouse
2018-01-06 11:49 ` [PATCH v5 09/12] x86/retpoline/irq32: " David Woodhouse
2018-01-06 11:49 ` [PATCH v5 10/12] x86/retpoline: Add boot time option to disable retpoline David Woodhouse
2018-01-06 11:49 ` [PATCH v5 11/12] x86/retpoline: Exclude objtool with retpoline David Woodhouse
2018-01-06 11:49 ` [PATCH v5 12/12] retpoline/modpost: Quieten MODVERSION retpoline build David Woodhouse
2018-01-07 0:10 ` [RFC PATCH 13/12] Retpoline vs. CONFIG_TRIM_UNUSED_SYMBOLS David Woodhouse
2018-01-07 8:03 ` David Woodhouse
2018-01-07 15:09 ` Lu, Hongjiu
2018-01-07 17:32 ` David Woodhouse
2018-01-07 17:57 ` Lu, Hongjiu
2018-01-07 18:18 ` Thomas Gleixner
2018-01-07 18:32 ` Lu, Hongjiu
2018-01-07 20:57 ` David Woodhouse
2018-01-07 22:16 ` David Woodhouse
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