linux-kernel - Re: [PATCH v3 13/13] KVM: x86: emulator/smm: preserve interrupt shadow in SMRAM

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Date:   Wed, 24 Aug 2022 23:50:03 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     Maxim Levitsky <mlevitsk@...hat.com>
Cc:     kvm@...r.kernel.org, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        linux-kernel@...r.kernel.org, Wanpeng Li <wanpengli@...cent.com>,
        Ingo Molnar <mingo@...hat.com>, x86@...nel.org,
        Jim Mattson <jmattson@...gle.com>,
        Kees Cook <keescook@...omium.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        "H. Peter Anvin" <hpa@...or.com>, Joerg Roedel <joro@...tes.org>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Paolo Bonzini <pbonzini@...hat.com>
Subject: Re: [PATCH v3 13/13] KVM: x86: emulator/smm: preserve interrupt
 shadow in SMRAM

On Wed, Aug 03, 2022, Maxim Levitsky wrote:
> @@ -518,7 +519,8 @@ struct kvm_smram_state_32 {
>  	u32 reserved1[62];
>  	u32 smbase;
>  	u32 smm_revision;
> -	u32 reserved2[5];
> +	u32 reserved2[4];
> +	u32 int_shadow; /* KVM extension */

Looking at this with fresh(er) eyes, I agree with Jim: KVM shouldn't add its own
fields in SMRAM.  There's no need to use vmcb/vmcs memory either, just add fields
in kvm_vcpu_arch to save/restore the state across SMI/RSM, and then borrow VMX's
approach of supporting migration by adding flags to do out-of-band migration,
e.g. KVM_STATE_NESTED_SMM_STI_BLOCKING and KVM_STATE_NESTED_SMM_MOV_SS_BLOCKING.

	/* SMM state that's not saved in SMRAM. */
	struct {
		struct {
			u8 interruptibility;
		} smm;
	} nested;

That'd finally give us an excuse to move nested_run_pending to common code too :-)