linux-kernel - Re: [RFC PATCH 00/18] KVM: VMX: Introduce Intel Mode-Based Execute Control (MBEC)

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Message-ID: <994de1c0-04c2-485b-bab0-909e293d1cf8@codelabs.ch>
Date: Wed, 23 Apr 2025 15:54:22 +0200
From: Adrian-Ken Rueegsegger <ken@...elabs.ch>
To: Jon Kohler <jon@...anix.com>
Cc: Alexander Grest <Alexander.Grest@...rosoft.com>,
 Nicolas Saenz Julienne <nsaenz@...zon.es>,
 "Madhavan T . Venkataraman" <madvenka@...ux.microsoft.com>,
 Mickaël Salaün <mic@...ikod.net>,
 Tao Su <tao1.su@...ux.intel.com>, Xiaoyao Li <xiaoyao.li@...el.com>,
 Zhao Liu <zhao1.liu@...el.com>, tglx@...utronix.de, mingo@...hat.com,
 bp@...en8.de, dave.hansen@...ux.intel.com, x86@...nel.org, hpa@...or.com,
 kvm@...r.kernel.org, linux-kernel@...r.kernel.org, seanjc@...gle.com,
 pbonzini@...hat.com
Subject: Re: [RFC PATCH 00/18] KVM: VMX: Introduce Intel Mode-Based Execute
 Control (MBEC)

Hi,

On 3/13/25 21:36, Jon Kohler wrote:

[snip]

> The semantics for EPT violation qualifications also change when MBEC
> is enabled, with bit 5 reflecting supervisor/kernel mode execute
> permissions and bit 6 reflecting user mode execute permissions.
> This ultimately serves to expose this feature to the L1 hypervisor,
> which consumes MBEC and informs the L2 partitions not to use the
> software MBEC by removing bit 14 in 0x40000004 EAX [4].

Should this say bit 13 of 0x40000004.EAX? According to the referenced 
docs [4]:

Bit 13: "Recommend using INT for MBEC system calls."

Bit 14: "Recommend a nested hypervisor using the enlightened VMCS 
interface. Also indicates that additional nested enlightenments may be 
available (see leaf 0x4000000A)."

Regards,
Adrian