linux-kernel - Re: [RFC PATCH v3 01/10] KVM: VMX: Virtualize Intel IA32_SPEC

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Date: Thu, 11 Apr 2024 21:07:31 -0700
From: Jim Mattson <jmattson@...gle.com>
To: Chao Gao <chao.gao@...el.com>
Cc: kvm@...r.kernel.org, linux-kernel@...r.kernel.org, 
	daniel.sneddon@...ux.intel.com, pawan.kumar.gupta@...ux.intel.com, 
	Sean Christopherson <seanjc@...gle.com>, Paolo Bonzini <pbonzini@...hat.com>, 
	Jonathan Corbet <corbet@....net>, 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>, linux-doc@...r.kernel.org
Subject: Re: [RFC PATCH v3 01/10] KVM: VMX: Virtualize Intel IA32_SPEC_CTRL

On Wed, Apr 10, 2024 at 7:35 AM Chao Gao <chao.gao@...el.com> wrote:
>
> From: Daniel Sneddon <daniel.sneddon@...ux.intel.com>
>
> Currently KVM disables interception of IA32_SPEC_CTRL after a non-0 is
> written to IA32_SPEC_CTRL by guest. The guest is allowed to write any
> value directly to hardware. There is a tertiary control for
> IA32_SPEC_CTRL. This control allows for bits in IA32_SPEC_CTRL to be
> masked to prevent guests from changing those bits.
>
> Add controls setting the mask for IA32_SPEC_CTRL and desired value for
> masked bits.
>
> These new controls are especially helpful for protecting guests that
> don't know about BHI_DIS_S and that are running on hardware that
> supports it. This allows the hypervisor to set BHI_DIS_S to fully
> protect the guest.
>
> Suggested-by: Sean Christopherson <seanjc@...gle.com>
> Signed-off-by: Daniel Sneddon <daniel.sneddon@...ux.intel.com>
> Signed-off-by: Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>
> [ add a new ioctl to report supported bits. Fix the inverted check ]
> Signed-off-by: Chao Gao <chao.gao@...el.com>

This looks quite Intel-centric. Isn't this feature essentially the
same as AMD's V_SPEC_CTRL? Can't we consolidate the code, rather than
having completely independent implementations for AMD and Intel?