From: "H. Peter Anvin" <hpa@zytor.com>
To: Ingo Molnar <mingo@kernel.org>, Borislav Petkov <bp@alien8.de>
Cc: Mike Galbraith <umgwanakikbuti@gmail.com>,
Ingo Molnar <mingo@elte.hu>, LKML <linux-kernel@vger.kernel.org>,
Thomas Gleixner <tglx@linutronix.de>,
Andy Lutomirski <luto@kernel.org>,
Denys Vlasenko <dvlasenk@redhat.com>,
Oleg Nesterov <oleg@redhat.com>, Dave Hansen <dave@sr71.net>
Subject: Re: [all better] Re: regression: massive trouble with fpu rework
Date: Mon, 29 Jun 2015 12:48:19 -0700 [thread overview]
Message-ID: <5591A103.6020104@zytor.com> (raw)
In-Reply-To: <20150629093504.GA20600@gmail.com>
On 06/29/2015 02:35 AM, Ingo Molnar wrote:
>
> Indeed, I bet that makes a difference!
>
> I wish that 'unmasking' logic came with more comments:
>
> - Why do BIOSen ever mask CPUIDs?
>
To work around bugs in legacy operating systems.
> - Why do we unmask the masking?
Because we don't have those specific bugs.
> - Why doesn't the kernel keep on working just fine even if certain CPUID aspects
> are turned off?
Because it exercises code paths that are otherwise impossible, for
example, it exposes the XSAVE capability without exposing the XSAVE
information in higher CPUID leaves.
The other option would be to have a list of CPU features that should be
turned off whenever the CPUID leaf maximum is too low, but it gives a
better user experience to just override the BIOS capping and then we
have fewer code paths in the kernel to worry about.
-hpa
next prev parent reply other threads:[~2015-06-29 19:49 UTC|newest]
Thread overview: 28+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-06-27 6:25 regression: massive trouble with fpu rework Mike Galbraith
2015-06-27 8:18 ` [all better] " Mike Galbraith
2015-06-27 8:25 ` Ingo Molnar
2015-06-27 8:55 ` Mike Galbraith
2015-06-27 9:37 ` Borislav Petkov
2015-06-27 11:01 ` Mike Galbraith
2015-06-27 21:02 ` Henrique de Moraes Holschuh
2015-06-28 3:11 ` Mike Galbraith
2015-06-28 15:06 ` Henrique de Moraes Holschuh
2015-06-28 15:39 ` Mike Galbraith
2015-06-29 1:12 ` Henrique de Moraes Holschuh
2015-06-29 6:40 ` Ingo Molnar
2015-06-29 8:25 ` Mike Galbraith
2015-06-29 8:33 ` Borislav Petkov
2015-06-29 8:41 ` Mike Galbraith
2015-06-29 9:35 ` Ingo Molnar
2015-06-29 9:57 ` Borislav Petkov
2015-06-29 19:48 ` H. Peter Anvin [this message]
2015-06-30 5:14 ` Ingo Molnar
2015-06-29 12:27 ` Mike Galbraith
2015-06-29 13:09 ` Borislav Petkov
2015-06-30 5:16 ` Ingo Molnar
2015-06-30 20:22 ` H. Peter Anvin
2015-07-09 13:13 ` Henrique de Moraes Holschuh
2015-06-29 19:50 ` H. Peter Anvin
2015-06-30 5:18 ` Ingo Molnar
2015-06-30 5:24 ` [tip:x86/urgent] x86/fpu: Fix FPU related boot regression when CPUID masking BIOS feature is enabled tip-bot for Ingo Molnar
2015-06-27 8:18 ` regression: massive trouble with fpu rework Ingo Molnar
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=5591A103.6020104@zytor.com \
--to=hpa@zytor.com \
--cc=bp@alien8.de \
--cc=dave@sr71.net \
--cc=dvlasenk@redhat.com \
--cc=linux-kernel@vger.kernel.org \
--cc=luto@kernel.org \
--cc=mingo@elte.hu \
--cc=mingo@kernel.org \
--cc=oleg@redhat.com \
--cc=tglx@linutronix.de \
--cc=umgwanakikbuti@gmail.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox