linux-kernel - Re: [PATCH v15 07/14] KVM: VMX: Emulate reads and writes to CET MSRs

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Date:   Wed, 3 Feb 2021 20:50:16 +0800
From:   Yang Weijiang <weijiang.yang@...el.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     Yang Weijiang <weijiang.yang@...el.com>, seanjc@...gle.com,
        jmattson@...gle.com, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, yu.c.zhang@...ux.intel.com
Subject: Re: [PATCH v15 07/14] KVM: VMX: Emulate reads and writes to CET MSRs

On Wed, Feb 03, 2021 at 12:57:41PM +0100, Paolo Bonzini wrote:
> On 03/02/21 12:34, Yang Weijiang wrote:
> > MSRs that are switched through XSAVES are especially annoying due to the
> > possibility of the kernel's FPU being used in IRQ context. Disable IRQs
> > and ensure the guest's FPU state is loaded when accessing such MSRs.
> 
> Good catch!  This should be in x86.h and named kvm_get/set_xsave_msr because
> it's not VMX specific.  The commit message should also be there as a
> comment.
Thanks a lot for reviewing! These words came from Sean! :-D
>
> In addition,
> 
> > +	case MSR_IA32_S_CET:
> > +		if (!cet_is_control_msr_accessible(vcpu, msr_info))
> > +			return 1;
> > +		msr_info->data = vmcs_readl(GUEST_S_CET);
> > +		break;
> > +	case MSR_IA32_U_CET:
> > +		if (!cet_is_control_msr_accessible(vcpu, msr_info))
> > +			return 1;
> > +		vmx_get_xsave_msr(msr_info);
> > +		break;
> 
> these two might as well be the same "case" for symmetry with the handling of
> WRMSR.
> 
> I've fixed this up locally, since these patches will not be pushed to Linus
> until the corresponding bare metal support is there.
Got it!
> 
> Paolo