linux-kernel - Re: [PATCH Part2 RFC v4 26/40] KVM: SVM: Add KVM_SEV_SNP_LAUNCH

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Date:   Fri, 16 Jul 2021 20:18:27 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     Brijesh Singh <brijesh.singh@....com>
Cc:     x86@...nel.org, linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        linux-efi@...r.kernel.org, platform-driver-x86@...r.kernel.org,
        linux-coco@...ts.linux.dev, linux-mm@...ck.org,
        linux-crypto@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Joerg Roedel <jroedel@...e.de>,
        Tom Lendacky <thomas.lendacky@....com>,
        "H. Peter Anvin" <hpa@...or.com>, Ard Biesheuvel <ardb@...nel.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Andy Lutomirski <luto@...nel.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Sergio Lopez <slp@...hat.com>, Peter Gonda <pgonda@...gle.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
        David Rientjes <rientjes@...gle.com>,
        Dov Murik <dovmurik@...ux.ibm.com>,
        Tobin Feldman-Fitzthum <tobin@....com>,
        Borislav Petkov <bp@...en8.de>,
        Michael Roth <michael.roth@....com>,
        Vlastimil Babka <vbabka@...e.cz>, tony.luck@...el.com,
        npmccallum@...hat.com, brijesh.ksingh@...il.com
Subject: Re: [PATCH Part2 RFC v4 26/40] KVM: SVM: Add
 KVM_SEV_SNP_LAUNCH_FINISH command

On Wed, Jul 07, 2021, Brijesh Singh wrote:
> +        struct kvm_sev_snp_launch_finish {
> +                __u64 id_block_uaddr;
> +                __u64 id_auth_uaddr;
> +                __u8 id_block_en;
> +                __u8 auth_key_en;
> +                __u8 host_data[32];

Pad this one too?

> +        };
> +
> +
> +See SEV-SNP specification for further details on launch finish input parameters.

...

> +	data->gctx_paddr = __psp_pa(sev->snp_context);
> +	ret = sev_issue_cmd(kvm, SEV_CMD_SNP_LAUNCH_FINISH, data, &argp->error);

Shouldn't KVM unwind everything it did if LAUNCH_FINISH fails?  And if that's
not possible, take steps to make the VM unusable?

> +
> +	kfree(id_auth);
> +
> +e_free_id_block:
> +	kfree(id_block);
> +
> +e_free:
> +	kfree(data);
> +
> +	return ret;
> +}
> +

...

> @@ -2346,8 +2454,25 @@ void sev_free_vcpu(struct kvm_vcpu *vcpu)
>  
>  	if (vcpu->arch.guest_state_protected)
>  		sev_flush_guest_memory(svm, svm->vmsa, PAGE_SIZE);
> +
> +	/*
> +	 * If its an SNP guest, then VMSA was added in the RMP entry as a guest owned page.
> +	 * Transition the page to hyperivosr state before releasing it back to the system.

"hyperivosr" typo.  And please wrap at 80 chars.

> +	 */
> +	if (sev_snp_guest(vcpu->kvm)) {
> +		struct rmpupdate e = {};
> +		int rc;
> +
> +		rc = rmpupdate(virt_to_page(svm->vmsa), &e);

So why does this not need to go through snp_page_reclaim()?

> +		if (rc) {
> +			pr_err("Failed to release SNP guest VMSA page (rc %d), leaking it\n", rc);

Seems like a WARN would be simpler.  But the more I see the rmpupdate(..., {0})
pattern, the more I believe that nuking an RMP entry needs a dedicated helper.

> +			goto skip_vmsa_free;