linux-kernel - Re: [PATCH] x86/cpu: Add a VMX flag to enumerate 5-level EPT support to userspace

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Message-ID: <ZZ6iu5v_nAYtrz7K@google.com>
Date: Wed, 10 Jan 2024 05:59:23 -0800
From: Sean Christopherson <seanjc@...gle.com>
To: Tao Su <tao1.su@...ux.intel.com>
Cc: Paolo Bonzini <pbonzini@...hat.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, kvm@...r.kernel.org, 
	linux-kernel@...r.kernel.org, Yi Lai <yi1.lai@...el.com>, 
	Xudong Hao <xudong.hao@...el.com>
Subject: Re: [PATCH] x86/cpu: Add a VMX flag to enumerate 5-level EPT support
 to userspace

On Wed, Jan 10, 2024, Tao Su wrote:
> On Tue, Jan 09, 2024 at 04:23:40PM -0800, Sean Christopherson wrote:
> > Add a VMX flag in /proc/cpuinfo, ept_5level, so that userspace can query
> > whether or not the CPU supports 5-level EPT paging.  EPT capabilities are
> > enumerated via MSR, i.e. aren't accessible to userspace without help from
> > the kernel, and knowing whether or not 5-level EPT is supported is sadly
> > necessary for userspace to correctly configure KVM VMs.
> > 
> > When EPT is enabled, bits 51:49 of guest physical addresses are consumed
> 
> nit: s/49/48

Argh, you even pointed that out before too.  Thanks!