linux-kernel - Re: [PATCH v14 10/13] KVM: x86: Enable CET virtualization for VMX and advertise CET to userspace

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Date:   Thu, 28 Jan 2021 18:53:29 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Yang Weijiang <weijiang.yang@...el.com>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, sean.j.christopherson@...el.com,
        jmattson@...gle.com
Cc:     yu.c.zhang@...ux.intel.com
Subject: Re: [PATCH v14 10/13] KVM: x86: Enable CET virtualization for VMX and
 advertise CET to userspace

On 06/11/20 02:16, Yang Weijiang wrote:
> 
> +
> +	if (((cr4 ^ old_cr4) & X86_CR4_CET) && kvm_cet_supported()) {
> +		vmcs_writel(GUEST_SSP, 0);
> +		vmcs_writel(GUEST_S_CET, 0);
> +		vmcs_writel(GUEST_INTR_SSP_TABLE, 0);
> +	}
> +

Is this behavior documented for bare metal?  I suspect it is at least 
not true for S_CET and INTR_SSP_TABLE, because SMM entry does not save 
those to SMRAM (and clears CR4.CET).

Also, you need to save/restore GUEST_SSP to SMRAM.

Paolo