From: Borislav Petkov <bp@alien8.de>
To: Andy Lutomirski <luto@amacapital.net>
Cc: Fenghua Yu <fenghua.yu@intel.com>,
Thomas Gleixner <tglx@linutronix.de>,
"x86@kernel.org" <x86@kernel.org>,
Dave Hansen <dave.hansen@linux.intel.com>,
"Bryan O'Donoghue" <pure.logic@nexus-software.ie>,
Andrew Morton <akpm@linux-foundation.org>,
Oleg Nesterov <oleg@redhat.com>, Ingo Molnar <mingo@kernel.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
Andy Shevchenko <andy.shevchenko@gmail.com>,
"H. Peter Anvin" <hpa@zytor.com>,
"Yu, Yu-cheng" <yu-cheng.yu@intel.com>,
Linus Torvalds <torvalds@linux-foundation.org>
Subject: Re: [PATCH] x86/FPU: Fix FPU handling on legacy FPU machines
Date: Sat, 12 Mar 2016 18:47:23 +0100 [thread overview]
Message-ID: <20160312174722.GE23410@pd.tnic> (raw)
In-Reply-To: <CALCETrXFDtZ9qkyaPTNqos+=Q8iDSxbjaC36ikg5dJBc8+sToA@mail.gmail.com>
On Sat, Mar 12, 2016 at 09:21:16AM -0800, Andy Lutomirski wrote:
> For reference, what are the QEMU options and boot options you used to
> trigger this? I'm asking because I tested eagerfpu=on without fxsr a
> few weeks ago in QEMU, and I didn't trigger it. Maybe I needed to
> force KVM off or something.
$ qemu-system-i386
-enable-kvm
-gdb tcp::1234
-cpu 486
-m 2048
-hda /home/boris/kvm/debian/sid-i386.img
-boot menu=off,order=c
-localtime
-net nic,model=rtl8139,macaddr=12:35:12:34:56:78
-net user,hostfwd=tcp::1235-:22
-usbdevice tablet
-kernel /home/boris/kernel/linux-2.6/arch/x86/boot/bzImage
-append "root=/dev/sda1 resume=/dev/sdb1 debug ignore_loglevel log_buf_len=16M earlyprintk=ttyS0,115200 console=ttyS0,115200 console=tty0 "
-monitor pty
-soundhw hda
-serial file:/home/boris/kvm/test-i386-1235.log
-snapshot
-name "Debian i386:1235"
-smp 1
-virtfs local,path=/tmp,mount_tag=tmp,security_model=none
I basically tried to get it as close to 486er as possible. I had also
CONFIG_M486=y for the guest kernel.
> Off the top of my head, I'm guessing that when I wrote "x86/fpu: Fix
> FNSAVE usage in eagerfpu mode", I was inadvertently using a bastardize
> combination of FNSAVE and FXRSTOR-of-init-state, KVM let the FXRSTOR
> through despite not advertising it in CPUID, and it papered over the
> init issue because the wrong init state format was hidden by using the
> wrong instruction to load it.
Yeah, I think qemu looks at CPUID bits for some stuff but probably not
all. And I also think we should go and fix such issues there so that we
can have as accurate an emulation as possible.
> Sigh. Yet more reason for Intel to add chicken bits to *turn off* new
> features.
Amen to that.
--
Regards/Gruss,
Boris.
ECO tip #101: Trim your mails when you reply.
next prev parent reply other threads:[~2016-03-12 17:47 UTC|newest]
Thread overview: 32+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-03-10 10:46 Got FPU related warning on Intel Quark during boot Andy Shevchenko
2016-03-10 11:19 ` Ingo Molnar
2016-03-10 12:48 ` Andy Shevchenko
2016-03-10 12:56 ` Borislav Petkov
2016-03-10 13:31 ` Andy Shevchenko
2016-03-10 14:59 ` Borislav Petkov
2016-03-10 15:22 ` Andy Shevchenko
2016-03-10 15:45 ` Bryan O'Donoghue
2016-03-10 16:49 ` Borislav Petkov
2016-03-10 17:15 ` Bryan O'Donoghue
2016-03-10 19:06 ` Borislav Petkov
2016-03-11 1:31 ` Andy Lutomirski
2016-03-11 10:50 ` Bryan O'Donoghue
2016-03-11 1:39 ` Andy Lutomirski
2016-03-11 9:08 ` Ingo Molnar
2016-03-11 9:48 ` Borislav Petkov
2016-03-11 11:02 ` Bryan O'Donoghue
2016-03-11 11:26 ` Borislav Petkov
2016-03-11 11:32 ` [PATCH] x86/FPU: Fix FPU handling on legacy FPU machines Borislav Petkov
2016-03-11 18:32 ` Linus Torvalds
2016-03-11 22:03 ` Borislav Petkov
2016-03-11 22:07 ` Dave Hansen
2016-03-11 22:20 ` Borislav Petkov
2016-03-12 17:21 ` Andy Lutomirski
2016-03-12 17:47 ` Borislav Petkov [this message]
2016-03-12 12:04 ` Bryan O'Donoghue
2016-03-12 12:27 ` Borislav Petkov
2016-03-12 15:17 ` Ingo Molnar
2016-03-22 22:03 ` Maciej W. Rozycki
2016-03-12 15:08 ` Ingo Molnar
2016-03-12 15:12 ` Ingo Molnar
2016-03-12 15:16 ` [tip:x86/urgent] x86/fpu: Fix eager-FPU " tip-bot for Borislav Petkov
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