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From: David Woodhouse <dwmw2@infradead.org>
To: Borislav Petkov <bp@alien8.de>, Tom Lendacky <thomas.lendacky@amd.com>
Cc: x86-ml <x86@kernel.org>,
	linux-tip-commits@vger.kernel.org, hpa@zytor.com,
	 gregkh@linuxfoundation.org, tglx@linutronix.de,
	linux-kernel@vger.kernel.org,  mingo@kernel.org
Subject: Re: [PATCH] x86/cpufeatures: Cleanup AMD speculation feature bits
Date: Fri, 26 Jan 2018 21:59:44 +0000	[thread overview]
Message-ID: <1517003984.30244.299.camel@infradead.org> (raw)
In-Reply-To: <20180126215209.vqdxh5p672tcdst6@pd.tnic>

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On Fri, 2018-01-26 at 22:52 +0100, Borislav Petkov wrote:
> On Fri, Jan 26, 2018 at 03:06:20PM -0600, Tom Lendacky wrote:
> > 
> > So I like the idea of AMD_IBRS/AMD_IBPB/AMD_STIBP and then use the magic
> > quotes as appropriate.  We could probably use the magic quotes on
> > AMD_STIBP and set X86_FEATURE_STIBP when we see X86_FEATURE_AMD_STIBP.
> Like this?
> 
> We set the respective Intel features when we detect the AMD ones so that
> we get correct /proc/cpuinfo strings. The respective AMD ones are not
> shown.
> 
> +
> +	if (cpu_has(c, X86_FEATURE_AMD_IBRS))
> +		set_cpu_cap(c, X86_FEATURE_IBRS);

No, there is no X86_FEATURE_IBRS; that was going to be the "we are
using IBRS" soft feature, analogous to X86_FEATURE_RETPOLINE and
X86_FEATURE_IBPB, actually used for the alternatives.

Intel doesn't *have* a feature bit for only IBRS. They have the bit
which indicates that *both* the SPEC_CTRL (with IBRS) and PRED_CMD
(with IBPB) registers are present.

If we wanted to do this kind of thing, we'd do it the other way round.
Turn the *Intel* feature into both 'IBRS' and 'IBPB' CPU-visible
features, and have those defined in the AMD word. Then use virtual bits
with "" for the software features, since we don't want *those* to
appear in /proc/cpuinfo.

I'll take a look at this in the morning.

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  reply	other threads:[~2018-01-26 21:59 UTC|newest]

Thread overview: 36+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-01-25 16:14 [PATCH v5 0/7] Basic Speculation Control feature support David Woodhouse
2018-01-25 16:14 ` [PATCH v5 1/7] x86/cpufeatures: Add CPUID_7_EDX CPUID leaf David Woodhouse
2018-01-26 14:59   ` [tip:x86/pti] " tip-bot for David Woodhouse
2018-01-25 16:14 ` [PATCH v5 2/7] x86/cpufeatures: Add Intel feature bits for Speculation Control David Woodhouse
2018-01-26 15:00   ` [tip:x86/pti] " tip-bot for David Woodhouse
2018-01-25 16:14 ` [PATCH v5 3/7] x86/cpufeatures: Add AMD " David Woodhouse
2018-01-25 21:30   ` Borislav Petkov
2018-01-25 21:37     ` Thomas Gleixner
2018-01-25 21:41     ` Borislav Petkov
2018-01-26 15:00   ` [tip:x86/pti] " tip-bot for David Woodhouse
2018-01-26 18:41     ` [PATCH] x86/cpufeatures: Cleanup AMD speculation feature bits Borislav Petkov
2018-01-26 18:45       ` David Woodhouse
2018-01-26 18:49         ` Borislav Petkov
2018-01-26 21:06           ` Tom Lendacky
2018-01-26 21:52             ` Borislav Petkov
2018-01-26 21:59               ` David Woodhouse [this message]
2018-01-26 22:10                 ` Borislav Petkov
2018-01-26 23:14                   ` Tom Lendacky
2018-01-27  8:49                     ` David Woodhouse
2018-01-27  9:27                     ` David Woodhouse
2018-01-27  9:37                       ` Borislav Petkov
2018-01-27 10:32                         ` David Woodhouse
2018-01-27 13:18                           ` Borislav Petkov
2018-01-25 16:14 ` [PATCH v5 4/7] x86/msr: Add definitions for new speculation control MSRs David Woodhouse
2018-01-26 15:00   ` [tip:x86/pti] " tip-bot for David Woodhouse
2018-01-25 16:14 ` [PATCH v5 5/7] x86/pti: Do not enable PTI on processors which are not vulnerable to Meltdown David Woodhouse
2018-01-25 18:10   ` Dave Hansen
2018-01-25 19:53     ` Dave Hansen
2018-01-25 22:00   ` Borislav Petkov
2018-01-26 15:01   ` [tip:x86/pti] x86/pti: Do not enable PTI on CPUs " tip-bot for David Woodhouse
2018-01-25 16:14 ` [PATCH v5 6/7] x86/cpufeature: Blacklist SPEC_CTRL/PRED_CMD on early Spectre v2 microcodes David Woodhouse
2018-01-26 15:01   ` [tip:x86/pti] " tip-bot for David Woodhouse
2018-01-25 16:14 ` [PATCH v5 7/7] x86/speculation: Add basic IBPB (Indirect Branch Prediction Barrier) support David Woodhouse
2018-01-26 15:02   ` [tip:x86/pti] " tip-bot for David Woodhouse
2018-01-26 16:18     ` David Woodhouse
2018-01-26 21:36   ` [PATCH v5 7/7] " Tim Chen

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