linux-kernel - Re: [PATCH 6/7] KVM: SVM: move MSR_IA32_SPEC

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Date:   Wed, 2 Nov 2022 08:28:14 -0700
From:   Josh Poimboeuf <jpoimboe@...nel.org>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        jmattson@...gle.com, seanjc@...gle.com
Subject: Re: [PATCH 6/7] KVM: SVM: move MSR_IA32_SPEC_CTRL save/restore to
 assembly

On Fri, Oct 28, 2022 at 07:07:22PM -0400, Paolo Bonzini wrote:
> +++ b/arch/x86/kvm/svm/svm.c
> @@ -3918,10 +3918,21 @@ static noinstr void svm_vcpu_enter_exit(struct kvm_vcpu *vcpu)
>  	struct vcpu_svm *svm = to_svm(vcpu);
>  	unsigned long vmcb_pa = svm->current_vmcb->pa;
>  
> +	/*
> +	 * For non-nested case:
> +	 * If the L01 MSR bitmap does not intercept the MSR, then we need to
> +	 * save it.
> +	 *
> +	 * For nested case:
> +	 * If the L02 MSR bitmap does not intercept the MSR, then we need to
> +	 * save it.
> +	 */
> +	bool spec_ctrl_intercepted = msr_write_intercepted(vcpu, MSR_IA32_SPEC_CTRL);

This triggers a warning:

  vmlinux.o: warning: objtool: svm_vcpu_enter_exit+0x3d: call to svm_msrpm_offset() leaves .noinstr.text section

svm_vcpu_enter_exit() is noinstr, but it's calling
msr_write_intercepted() which is not.

That's why in the VMX code I did the call to msr_write_intercepted() (in
__vmx_vcpu_run_flags) before calling vmx_vcpu_enter_exit().

-- 
Josh