linux-kernel - Re: [PATCH] x86/xen: disable CPU idle and frequency drivers for PVH dom0

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Message-ID: <99ad29b0-e57e-454e-b9b8-63b33f25ab45@amd.com>
Date: Mon, 7 Apr 2025 10:13:50 -0400
From: Jason Andryuk <jason.andryuk@....com>
To: Roger Pau Monne <roger.pau@...rix.com>, <xen-devel@...ts.xenproject.org>,
	<linux-kernel@...r.kernel.org>
CC: Stefano Stabellini <sstabellini@...nel.org>, <Xenia.Ragiadakou@....com>,
	<Alejandro.GarciaVallejo@....com>, Juergen Gross <jgross@...e.com>, "Boris
 Ostrovsky" <boris.ostrovsky@...cle.com>, Thomas Gleixner
	<tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>, Borislav Petkov
	<bp@...en8.de>, Dave Hansen <dave.hansen@...ux.intel.com>, <x86@...nel.org>,
	"H. Peter Anvin" <hpa@...or.com>
Subject: Re: [PATCH] x86/xen: disable CPU idle and frequency drivers for PVH
 dom0

On 2025-04-07 06:18, Roger Pau Monne wrote:
> When running as a PVH dom0 the ACPI tables exposed to Linux are (mostly)
> the native ones, thus exposing the C and P states, that can lead to
> attachment of CPU idle and frequency drivers.  However the entity in
> control of the CPU C and P states is Xen, as dom0 doesn't have a full view
> of the system load, neither has all CPUs assigned and identity pinned.
> 
> Like it's done for classic PV guests, prevent Linux from using idle or
> frequency state drivers when running as a PVH dom0.
> 
> On an AMD EPYC 7543P system without this fix a Linux PVH dom0 will keep the
> host CPUs spinning at 100% even when dom0 is completely idle, as it's
> attempting to use the acpi_idle driver.
> 
> Signed-off-by: Roger Pau Monné <roger.pau@...rix.com>

Reviewed-by: Jason Andryuk <jason.andryuk@....com>

Thanks,
Jason