linux-kernel - Re: [RFC PATCH] x86/bhyve: Detect FreeBSD Bhyve hypervisor

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Message-ID: <aJ4UEO3gRUiuD-4F@lx-t490>
Date: Thu, 14 Aug 2025 18:51:28 +0200
From: "Ahmed S. Darwish" <darwi@...utronix.de>
To: David Woodhouse <dwmw2@...radead.org>
Cc: Borislav Petkov <bp@...en8.de>, Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
	"H. Peter Anvin" <hpa@...or.com>, linux-kernel@...r.kernel.org,
	Konstantin Belousov <kib@....kiev.ua>,
	John Baldwin <jhb@...ebsd.org>
Subject: Re: [RFC PATCH] x86/bhyve: Detect FreeBSD Bhyve hypervisor

On Thu, 14 Aug 2025, David Woodhouse wrote:
> On Thu, 2025-08-14 at 12:15 +0200, Borislav Petkov wrote:
>
> >
> > Which makes it, what, 0x4000_0001?
> >
> > I presume there's an agreement among all the hypervisors...?
>
> There is no such agreement about CPUID; by *coincidence* most of them
> seem to use 0x4000_0?01 as their feature leaf, but the feature bits in
> each such leaf are completely different and the guest doesn't look at a
> given leaf unless it knows that specific hypervisor. Which is why the
> 15-bit enlightenment is advertised differently by each hypervisor
> despite being precisely the same enlightenment across them all.
>

For what it takes, such hypervisor leaves, in the 0x40000000 range, will
be converted by the ongoing x86-cpuid-db CPUID parser work at some point.

(Another iteration of the CPUID parser is to be posted today.)

Thanks,
Ahmed