linux-kernel - Re: [tip:x86/cpu] x86, AMD: Enable WC+ memory type on family 10 processors

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Message-ID: <20130213003126.GD15988@pd.tnic>
Date:	Wed, 13 Feb 2013 01:31:26 +0100
From:	Borislav Petkov <bp@...en8.de>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	mingo@...nel.org, linux-kernel@...r.kernel.org,
	boris.ostrovsky@....com, tglx@...utronix.de, hpa@...ux.intel.com,
	linux-tip-commits@...r.kernel.org,
	Pekka Enberg <penberg@...nel.org>, kvm@...r.kernel.org
Subject: Re: [tip:x86/cpu] x86, AMD: Enable WC+ memory type on family 10
 processors

On Tue, Feb 12, 2013 at 04:21:13PM -0800, H. Peter Anvin wrote:
> On 02/12/2013 04:16 PM, Borislav Petkov wrote:
> >
> >This family check is redundant, we're already in a 0x10 if-branch
> >above. Boris had sent a second version which doesn't have that check:
> >http://marc.info/?l=linux-kernel&m=135949774114910 but I don't know how this
> >other version has gotten in.
> >
> >@hpa: maybe replace - patch is still at the top of tip:x86/cpu?
> >
> 
> I'll check with Ingo if that is doable.
> 
> >>+			rdmsrl(MSR_AMD64_BU_CFG2, value);
> >>+			value &= ~(1ULL << 24);
> >>+			wrmsrl(MSR_AMD64_BU_CFG2, value);
> >>+		}
> >>  	}
> >>
> >>  	rdmsr_safe(MSR_AMD64_PATCH_LEVEL, &c->microcode, &dummy);
> >
> >However, the more serious issue is that that same kernel #GPs when
> >booted in kvm. It seems it cannot stomach that specific MSR, see the
> >second "<-- trapping instruction" below and that BU_CFG2 MSR landing in
> >%ecx in the line before that.
> >
> >Oh, and this happens only with the kvm executable (/usr/bin/kvm) in
> >debian testing. If I use qemu from git, it passes over init_amd just
> >fine.
> >
> >Hmmm..
> >
> 
> It #GPs on an MSR, which tends to be a bug in the VMM; RDMSR/WRMSR
> generally kick out to the VMM.  There isn't a huge lot of work we
> can do about that...

Yeah, kvm.ko which runs on the host says that it ignores this MSR:

[160716.170333] kvm [29093]: vcpu0 unhandled rdmsr: 0xc001102a

> I think Qemu defaults to ignoring unknown-to-it MSRs whereas maybe
> kvmtool croaks?  Pekka?

Actually that's the qemu kvm thing you get from http://www.linux-kvm.org
not the kvmtool.

Let me add the kvm ML to CC.

Guys, when I start the guest in kvm, it #GPs early when
it tries to RDMSR 0xc001102a. Here's the oops message:
http://marc.info/?l=linux-kernel&m=136071460803452

qemu-kvm is qemu-kvm (1.1.2+dfsg-5) from debian testing. Command line is:

kvm -snapshot -gdb tcp::1234 -cpu phenom -hda /home/boris/kvm/debian/sid-x86_64.img -name "Debian x86_64:1235" -boot menu=off,order=c -m 2048 -localtime -net nic -net user,hostfwd=tcp::1235-:22 -usbdevice tablet -kernel /w/kernel/linux-2.6/arch/x86/boot/bzImage -append "vga=0 root=/dev/sda1 debug ignore_loglevel console=ttyS0,115200 console=tty0" -serial file:/home/boris/kvm/test-x86_64.log

Any ideas?

-- 
Regards/Gruss,
    Boris.

Sent from a fat crate under my desk. Formatting is fine.
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