linux-kernel - Re: [PATCH] processor passthru - upload _Cx and

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Date:	Fri, 24 Feb 2012 10:08:07 -0500
From:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
To:	Jan Beulich <JBeulich@...e.com>
Cc:	ke.yu@...el.com, kevin.tian@...el.com, lenb@...nel.org,
	xen-devel@...ts.xensource.com, linux-acpi@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] processor passthru - upload _Cx and _Pxx data to
 hypervisor (v5).

On Fri, Feb 24, 2012 at 10:23:42AM +0000, Jan Beulich wrote:
> >>> On 23.02.12 at 23:31, Konrad Rzeszutek Wilk <konrad.wilk@...cle.com> wrote:
> > This module (processor-passthru)  collects the information that the cpufreq
> > drivers and the ACPI processor code save in the 'struct acpi_processor' and
> > then uploads it to the hypervisor.
> 
> Thus looks conceptually wrong to me - there shouldn't be a need for a
> CPUFreq driver to be loaded in Dom0 (or your module should masquerade
> as the one and only suitable one).

I piggyback on the generic cpufreq drivers to collect the information they
have evaluated.

I can make the driver a cpufreq one but there does not seem to be a way
from the kernel to force a specific driver to say "use me". I could write
it naturally, but not sure what the usage case is except for the driver
I wrote. But perhaps there is also for the cpufreq powernow-k8 and acpi-processor
so that they can function without the need for strict compile order
(where powernow-k8 MUST be loaded before acpi-processor).

> 
> > On the hypervisor side, it requires this patch on AMD:
> > # HG changeset patch
> > # Parent aea8cfac8cf1afe397f2e1d422a852008d8a83fe
> > traps: AMD PM RDMSRs (MSR_K8_PSTATE_CTRL, etc)
> > 
> > The restriction to read and write the AMD power management MSRs is gated if 
> > the
> > domain 0 is the PM domain (so FREQCTL_dom0_kernel is set). But we can
> > relax this restriction and allow the privileged domain to read the MSRs
> > (but not write). This allows the priviliged domain to harvest the power
> > management information (ACPI _PSS states) and send it to the hypervisor.
> 
> Why would accessing these MSRs be necessary here, when it isn't
> for non-pvops? Perhaps only because you want a CPUFreq driver
> loaded?

Correct. The powernow-k8
> 
> Jan
> 
> > This patch works fine with older classic dom0 (2.6.32) and with
> > AMD K7 and K8 boxes.
> > 
> > Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
> > diff -r aea8cfac8cf1 xen/arch/x86/traps.c
> > --- a/xen/arch/x86/traps.c	Thu Feb 23 13:23:02 2012 -0500
> > +++ b/xen/arch/x86/traps.c	Thu Feb 23 13:29:00 2012 -0500
> > @@ -2484,7 +2484,7 @@ static int emulate_privileged_op(struct 
> >          case MSR_K8_PSTATE7:
> >              if ( boot_cpu_data.x86_vendor != X86_VENDOR_AMD )
> >                  goto fail;
> > -            if ( !is_cpufreq_controller(v->domain) )
> > +            if ( !is_cpufreq_controller(v->domain) && !IS_PRIV(v->domain) )
> >              {
> >                  regs->eax = regs->edx = 0;
> >                  break;
> 
> 
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