From: Borislav Petkov <bp@alien8.de>
To: Andy Lutomirski <luto@kernel.org>, Thomas Gleixner <tglx@linutronix.de>
Cc: x86@kernel.org, One Thousand Gnomes <gnomes@lxorguk.ukuu.org.uk>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
Brian Gerst <brgerst@gmail.com>,
Matthew Whitehead <tedheadster@gmail.com>
Subject: Re: [RFC PATCH 3/6] x86/cpu: Re-apply forced caps every time cpu caps are re-read
Date: Tue, 6 Dec 2016 09:57:26 +0100 [thread overview]
Message-ID: <20161206085726.b6jaxmtjse5oa2od@pd.tnic> (raw)
In-Reply-To: <e04d96bf465d5153aa29fb885fc038c254c441f1.1480985979.git.luto@kernel.org>
On Mon, Dec 05, 2016 at 05:01:12PM -0800, Andy Lutomirski wrote:
> Calling get_cpu_cap() will reset a bunch of CPU features. This will
> cause the system to lose track of force-set and force-cleared
> featueres in the words that are reset until the end of CPU
> initialization. This can cause X86_FEATURE_FPU, for example, to
> change back and forth during boot and potentially confuse CPU setup.
>
> To minimize the chance of confusion, re-apply forced caps every time
> get_cpu_cap() is called.
>
> Signed-off-by: Andy Lutomirski <luto@kernel.org>
> ---
> arch/x86/kernel/cpu/common.c | 7 +++++++
> 1 file changed, 7 insertions(+)
>
> diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
> index 347ae0a19380..24e1e4004d42 100644
> --- a/arch/x86/kernel/cpu/common.c
> +++ b/arch/x86/kernel/cpu/common.c
> @@ -758,6 +758,13 @@ void get_cpu_cap(struct cpuinfo_x86 *c)
> c->x86_capability[CPUID_8000_000A_EDX] = cpuid_edx(0x8000000a);
>
> init_scattered_cpuid_features(c);
> +
> + /*
> + * Clear/Set all flags overridden by options, after probe.
> + * This needs to happen each time we re-probe, which may happen
> + * several times during CPU initialization.
> + */
> + apply_forced_caps(c);
I guess...
Although I have to say all that early capabilities detection has grown
a lot of cruft during the years and is nuts. And calling get_cpu_cap()
multiple times is simply plain wrong.
What we should do is read CPUID *once*, filter out caps and set our
internal representation bits and be done with it.
Stuff like setup_pku() which *sets* CPUID bits will then have to run
*before* we do the detection and that's it.
But I guess that's future work.
--
Regards/Gruss,
Boris.
Good mailing practices for 400: avoid top-posting and trim the reply.
next prev parent reply other threads:[~2016-12-06 8:57 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-12-06 1:01 [RFC PATCH 0/6] CPUID and FPU fixes Andy Lutomirski
2016-12-06 1:01 ` [RFC PATCH 1/6] x86/CPU: Add X86_FEATURE_CPUID Andy Lutomirski
2016-12-06 8:08 ` Borislav Petkov
2016-12-06 1:01 ` [RFC PATCH 2/6] x86/cpu: Factor out application of forced cpu caps Andy Lutomirski
2016-12-06 8:32 ` Borislav Petkov
2016-12-06 1:01 ` [RFC PATCH 3/6] x86/cpu: Re-apply forced caps every time cpu caps are re-read Andy Lutomirski
2016-12-06 8:57 ` Borislav Petkov [this message]
2016-12-06 1:01 ` [RFC PATCH 4/6] x86/fpu: Fix "x86/fpu: Legacy x87 FPU detected" message Andy Lutomirski
2016-12-06 9:24 ` Borislav Petkov
2016-12-06 17:59 ` Andy Lutomirski
2016-12-06 18:04 ` Borislav Petkov
2016-12-06 1:01 ` [RFC PATCH 5/6] x86/fpu: Fix CPUID-less FPU detection Andy Lutomirski
2016-12-06 9:40 ` Borislav Petkov
2016-12-06 17:52 ` Andy Lutomirski
2016-12-07 9:42 ` Borislav Petkov
2016-12-06 1:01 ` [RFC PATCH 6/6] x86/fpu: Fix the "Giving up, no FPU found" test Andy Lutomirski
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