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

From: Borislav Petkov
Date: Tue Feb 12 2013 - 19:31:37 EST

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:
> > 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
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:

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?


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