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

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Date:	Fri, 24 Feb 2012 10:23:42 +0000
From:	"Jan Beulich" <JBeulich@...e.com>
To:	"Konrad Rzeszutek Wilk" <konrad.wilk@...cle.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 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).

> 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?

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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