linux-kernel - Re: [PATCH v15 04/41] KVM: x86: Introduce KVM_{G,S}ET_ONE

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Message-ID: <b328aae7-ba4f-4710-a65a-79e670f92ca2@intel.com>
Date: Mon, 15 Sep 2025 14:29:00 +0800
From: Xiaoyao Li <xiaoyao.li@...el.com>
To: Sean Christopherson <seanjc@...gle.com>,
 Paolo Bonzini <pbonzini@...hat.com>
Cc: kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
 Tom Lendacky <thomas.lendacky@....com>,
 Mathias Krause <minipli@...ecurity.net>, John Allen <john.allen@....com>,
 Rick Edgecombe <rick.p.edgecombe@...el.com>, Chao Gao <chao.gao@...el.com>,
 Maxim Levitsky <mlevitsk@...hat.com>, Zhang Yi Z <yi.z.zhang@...ux.intel.com>
Subject: Re: [PATCH v15 04/41] KVM: x86: Introduce KVM_{G,S}ET_ONE_REG uAPIs
 support

On 9/13/2025 7:22 AM, Sean Christopherson wrote:
> From: Yang Weijiang <weijiang.yang@...el.com>
> 
> Enable KVM_{G,S}ET_ONE_REG uAPIs so that userspace can access MSRs and
> other non-MSR registers through them, along with support for
> KVM_GET_REG_LIST to enumerate support for KVM-defined registers.
> 
> This is in preparation for allowing userspace to read/write the guest SSP
> register, which is needed for the upcoming CET virtualization support.
> 
> Currently, two types of registers are supported: KVM_X86_REG_TYPE_MSR and
> KVM_X86_REG_TYPE_KVM. All MSRs are in the former type; the latter type is
> added for registers that lack existing KVM uAPIs to access them. The "KVM"
> in the name is intended to be vague to give KVM flexibility to include
> other potential registers.  More precise names like "SYNTHETIC" and
> "SYNTHETIC_MSR" were considered, but were deemed too confusing (e.g. can
> be conflated with synthetic guest-visible MSRs) and may put KVM into a
> corner (e.g. if KVM wants to change how a KVM-defined register is modeled
> internally).
> 
> Enumerate only KVM-defined registers in KVM_GET_REG_LIST to avoid
> duplicating KVM_GET_MSR_INDEX_LIST, and so that KVM can return _only_
> registers that are fully supported (KVM_GET_REG_LIST is vCPU-scoped, i.e.
> can be precise, whereas KVM_GET_MSR_INDEX_LIST is system-scoped).
> 
> Suggested-by: Sean Christopherson <seanjc@...gle.com>
> Signed-off-by: Yang Weijiang <weijiang.yang@...el.com>
> Link: https://lore.kernel.org/all/20240219074733.122080-18-weijiang.yang@intel.com [1]
> Tested-by: Mathias Krause <minipli@...ecurity.net>
> Tested-by: John Allen <john.allen@....com>
> Tested-by: Rick Edgecombe <rick.p.edgecombe@...el.com>
> Signed-off-by: Chao Gao <chao.gao@...el.com>
> Co-developed-by: Sean Christopherson <seanjc@...gle.com>
> Signed-off-by: Sean Christopherson <seanjc@...gle.com>

Reviewed-by: Xiaoyao Li <xiaoyao.li@...el.com>