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From: Sean Christopherson <seanjc@google.com>
To: Brijesh Singh <brijesh.singh@amd.com>
Cc: x86@kernel.org, linux-kernel@vger.kernel.org,
	kvm@vger.kernel.org, linux-efi@vger.kernel.org,
	platform-driver-x86@vger.kernel.org, linux-coco@lists.linux.dev,
	linux-mm@kvack.org, linux-crypto@vger.kernel.org,
	Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@redhat.com>, Joerg Roedel <jroedel@suse.de>,
	Tom Lendacky <thomas.lendacky@amd.com>,
	"H. Peter Anvin" <hpa@zytor.com>,
	Ard Biesheuvel <ardb@kernel.org>,
	Paolo Bonzini <pbonzini@redhat.com>,
	Vitaly Kuznetsov <vkuznets@redhat.com>,
	Wanpeng Li <wanpengli@tencent.com>,
	Jim Mattson <jmattson@google.com>,
	Andy Lutomirski <luto@kernel.org>,
	Dave Hansen <dave.hansen@linux.intel.com>,
	Sergio Lopez <slp@redhat.com>, Peter Gonda <pgonda@google.com>,
	Peter Zijlstra <peterz@infradead.org>,
	Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>,
	David Rientjes <rientjes@google.com>,
	Dov Murik <dovmurik@linux.ibm.com>,
	Tobin Feldman-Fitzthum <tobin@ibm.com>,
	Borislav Petkov <bp@alien8.de>,
	Michael Roth <michael.roth@amd.com>,
	Vlastimil Babka <vbabka@suse.cz>,
	tony.luck@intel.com, npmccallum@redhat.com,
	brijesh.ksingh@gmail.com
Subject: Re: [PATCH Part2 RFC v4 38/40] KVM: SVM: Provide support for SNP_GUEST_REQUEST NAE event
Date: Mon, 19 Jul 2021 22:50:02 +0000	[thread overview]
Message-ID: <YPYBmlCuERUIO5+M@google.com> (raw)
In-Reply-To: <20210707183616.5620-39-brijesh.singh@amd.com>

On Wed, Jul 07, 2021, Brijesh Singh wrote:
> Version 2 of GHCB specification added the support two SNP Guest Request
> Message NAE event. The events allows for an SEV-SNP guest to make request
> to the SEV-SNP firmware through hypervisor using the SNP_GUEST_REQUEST
> API define in the SEV-SNP firmware specification.

IIUC, this snippet in the spec means KVM can't restrict what requests are made
by the guests.  If so, that makes it difficult to detect/ratelimit a misbehaving
guest, and also limits our options if there are firmware issues (hopefully there
aren't).  E.g. ratelimiting a guest after KVM has explicitly requested it to
migrate is not exactly desirable.

  The hypervisor cannot alter the messages without detection nor read the
  plaintext of the messages.

> The SNP_GUEST_REQUEST requires two unique pages, one page for the request
> and one page for the response. The response page need to be in the firmware
> state. The GHCB specification says that both the pages need to be in the
> hypervisor state but before executing the SEV-SNP command the response page
> need to be in the firmware state.
 
...

> Now that KVM supports all the VMGEXIT NAEs required for the base SEV-SNP
> feature, set the hypervisor feature to advertise it.

It would helpful if this changelog listed the Guest Requests that are required
for "base" SNP, e.g. to provide some insight as to why we care about guest
requests.

>  static int snp_bind_asid(struct kvm *kvm, int *error)
> @@ -1618,6 +1631,12 @@ static int snp_launch_start(struct kvm *kvm, struct kvm_sev_cmd *argp)
>  	if (rc)
>  		goto e_free_context;
>  
> +	/* Used for rate limiting SNP guest message request, use the default settings */
> +	ratelimit_default_init(&sev->snp_guest_msg_rs);

Is this exposed to userspace in any way?  This feels very much like a knob that
needs to be configurable per-VM.

Also, what are the estimated latencies of a guest request?  If the worst case
latency is >200ms, a default ratelimit frequency of 5hz isn't going to do a whole
lot.

> +static void snp_handle_guest_request(struct vcpu_svm *svm, struct ghcb *ghcb,
> +				     gpa_t req_gpa, gpa_t resp_gpa)
> +{
> +	struct sev_data_snp_guest_request data = {};
> +	struct kvm_vcpu *vcpu = &svm->vcpu;
> +	struct kvm *kvm = vcpu->kvm;
> +	struct kvm_sev_info *sev;
> +	int rc, err = 0;
> +
> +	if (!sev_snp_guest(vcpu->kvm)) {
> +		rc = -ENODEV;
> +		goto e_fail;
> +	}
> +
> +	sev = &to_kvm_svm(kvm)->sev_info;
> +
> +	if (!__ratelimit(&sev->snp_guest_msg_rs)) {
> +		pr_info_ratelimited("svm: too many guest message requests\n");
> +		rc = -EAGAIN;

What guarantee do we have that the guest actually understands -EAGAIN?  Ditto
for -EINVAL returned by snp_build_guest_buf().  AFAICT, our options are to return
one of the error codes defined in "Table 95. Status Codes for SNP_GUEST_REQUEST"
of the firmware ABI, kill the guest, or ratelimit the guest without returning
control to the guest.

> +		goto e_fail;
> +	}
> +
> +	rc = snp_build_guest_buf(svm, &data, req_gpa, resp_gpa);
> +	if (rc)
> +		goto e_fail;
> +
> +	sev = &to_kvm_svm(kvm)->sev_info;
> +
> +	mutex_lock(&kvm->lock);

Question on the VMPCK sequences.  The firmware ABI says:

   Each guest has four VMPCKs ... Each message contains a sequence number per
   VMPCK. The sequence number is incremented with each message sent. Messages
   sent by the guest to the firmware and by the firmware to the guest must be
   delivered in order. If not, the firmware will reject subsequent messages ...

Does that mean there are four independent sequences, i.e. four streams the guest
can use "concurrently", or does it mean the overall freshess/integrity check is
composed from four VMPCK sequences, all of which must be correct for the message
to be valid?

If it's the latter, then a traditional mutex isn't really necessary because the
guest must implement its own serialization, e.g. it's own mutex or whatever, to
ensure there is at most one request in-flight at any given time.  And on the KVM
side it means KVM can simpy reject requests if there is already an in-flight
request.  It might also give us more/better options for ratelimiting?

> +	rc = sev_issue_cmd(kvm, SEV_CMD_SNP_GUEST_REQUEST, &data, &err);
> +	if (rc) {
> +		mutex_unlock(&kvm->lock);

I suspect you reused this pattern from other, more complex code, but here it's
overkill.  E.g.

	if (!rc)
		rc = kvm_write_guest(kvm, resp_gpa, sev->snp_resp_page, PAGE_SIZE);
	else if (err)
		rc = err;

	mutex_unlock(&kvm->lock);

	ghcb_set_sw_exit_info_2(ghcb, rc);

> +		/* If we have a firmware error code then use it. */
> +		if (err)
> +			rc = err;
> +
> +		goto e_fail;
> +	}
> +
> +	/* Copy the response after the firmware returns success. */
> +	rc = kvm_write_guest(kvm, resp_gpa, sev->snp_resp_page, PAGE_SIZE);
> +
> +	mutex_unlock(&kvm->lock);
> +
> +e_fail:
> +	ghcb_set_sw_exit_info_2(ghcb, rc);
> +}
> +
> +static void snp_handle_ext_guest_request(struct vcpu_svm *svm, struct ghcb *ghcb,
> +					 gpa_t req_gpa, gpa_t resp_gpa)
> +{
> +	struct sev_data_snp_guest_request req = {};
> +	struct kvm_vcpu *vcpu = &svm->vcpu;
> +	struct kvm *kvm = vcpu->kvm;
> +	unsigned long data_npages;
> +	struct kvm_sev_info *sev;
> +	unsigned long err;
> +	u64 data_gpa;
> +	int rc;
> +
> +	if (!sev_snp_guest(vcpu->kvm)) {
> +		rc = -ENODEV;
> +		goto e_fail;
> +	}
> +
> +	sev = &to_kvm_svm(kvm)->sev_info;
> +
> +	if (!__ratelimit(&sev->snp_guest_msg_rs)) {
> +		pr_info_ratelimited("svm: too many guest message requests\n");
> +		rc = -EAGAIN;
> +		goto e_fail;
> +	}
> +
> +	if (!sev->snp_certs_data) {
> +		pr_err("svm: certs data memory is not allocated\n");
> +		rc = -EFAULT;

Another instance where the kernel's error numbers will not suffice.

> +		goto e_fail;
> +	}
> +
> +	data_gpa = ghcb_get_rax(ghcb);
> +	data_npages = ghcb_get_rbx(ghcb);

  reply	other threads:[~2021-07-19 22:50 UTC|newest]

Thread overview: 176+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-07-07 18:35 [PATCH Part2 RFC v4 00/40] Add AMD Secure Nested Paging (SEV-SNP) Hypervisor Support Brijesh Singh
2021-07-07 18:35 ` [PATCH Part2 RFC v4 01/40] KVM: SVM: Add support to handle AP reset MSR protocol Brijesh Singh
2021-07-14 20:17   ` Sean Christopherson
2021-07-15  7:39     ` Joerg Roedel
2021-07-15 13:42     ` Tom Lendacky
2021-07-15 15:45       ` Sean Christopherson
2021-07-15 17:05         ` Tom Lendacky
2021-07-07 18:35 ` [PATCH Part2 RFC v4 02/40] KVM: SVM: Provide the Hypervisor Feature support VMGEXIT Brijesh Singh
2021-07-14 20:37   ` Sean Christopherson
2021-07-14 21:00     ` Brijesh Singh
2021-07-07 18:35 ` [PATCH Part2 RFC v4 03/40] x86/cpufeatures: Add SEV-SNP CPU feature Brijesh Singh
2021-07-07 18:35 ` [PATCH Part2 RFC v4 04/40] x86/sev: Add the host SEV-SNP initialization support Brijesh Singh
2021-07-14 21:07   ` Sean Christopherson
2021-07-14 22:02     ` Brijesh Singh
2021-07-14 22:06       ` Sean Christopherson
2021-07-14 22:11         ` Brijesh Singh
2021-07-07 18:35 ` [PATCH Part2 RFC v4 05/40] x86/sev: Add RMP entry lookup helpers Brijesh Singh
2021-07-15 18:37   ` Sean Christopherson
2021-07-15 19:28     ` Brijesh Singh
2021-07-16 17:22       ` Brijesh Singh
2021-07-20 22:06         ` Sean Christopherson
2021-07-20 23:10           ` Brijesh Singh
2021-07-07 18:35 ` [PATCH Part2 RFC v4 06/40] x86/sev: Add helper functions for RMPUPDATE and PSMASH instruction Brijesh Singh
2021-07-12 18:44   ` Peter Gonda
2021-07-12 19:00     ` Dave Hansen
2021-07-15 18:56       ` Sean Christopherson
2021-07-15 19:08         ` Dave Hansen
2021-07-15 19:18           ` Sean Christopherson
2021-07-07 18:35 ` [PATCH Part2 RFC v4 07/40] x86/sev: Split the physmap when adding the page in RMP table Brijesh Singh
2021-07-14 22:25   ` Sean Christopherson
2021-07-15 17:05     ` Brijesh Singh
2021-07-15 17:51       ` Sean Christopherson
2021-07-15 18:14         ` Brijesh Singh
2021-07-15 18:39           ` Sean Christopherson
2021-07-15 19:38             ` Brijesh Singh
2021-07-15 22:01               ` Sean Christopherson
2021-07-15 22:11                 ` Brijesh Singh
2021-07-30 11:31               ` Vlastimil Babka
2021-07-30 16:10                 ` Brijesh Singh
2021-07-07 18:35 ` [PATCH Part2 RFC v4 08/40] x86/traps: Define RMP violation #PF error code Brijesh Singh
2021-07-15 19:02   ` Sean Christopherson
2021-07-15 19:16     ` Dave Hansen
2021-07-07 18:35 ` [PATCH Part2 RFC v4 09/40] x86/fault: Add support to dump RMP entry on fault Brijesh Singh
2021-07-07 19:21   ` Dave Hansen
2021-07-08 15:02     ` Brijesh Singh
2021-07-08 15:30       ` Dave Hansen
2021-07-08 16:48         ` Brijesh Singh
2021-07-08 16:58           ` Dave Hansen
2021-07-08 17:11             ` Brijesh Singh
2021-07-08 17:15               ` Dave Hansen
2021-07-07 18:35 ` [PATCH Part2 RFC v4 10/40] x86/fault: Add support to handle the RMP fault for user address Brijesh Singh
2021-07-08 16:16   ` Dave Hansen
2021-07-12 15:43     ` Brijesh Singh
2021-07-12 16:00       ` Dave Hansen
2021-07-12 16:11         ` Brijesh Singh
2021-07-12 16:15           ` Dave Hansen
2021-07-12 16:24             ` Brijesh Singh
2021-07-12 16:29               ` Dave Hansen
2021-07-12 16:49                 ` Brijesh Singh
2021-07-15 21:53                   ` Sean Christopherson
2021-07-30 16:00   ` Vlastimil Babka
2021-07-30 16:31     ` Dave Hansen
2021-07-07 18:35 ` [PATCH Part2 RFC v4 11/40] crypto:ccp: Define the SEV-SNP commands Brijesh Singh
2021-07-07 18:35 ` [PATCH Part2 RFC v4 12/40] crypto: ccp: Add support to initialize the AMD-SP for SEV-SNP Brijesh Singh
2021-07-07 18:35 ` [PATCH Part2 RFC v4 13/40] crypto: ccp: Shutdown SNP firmware on kexec Brijesh Singh
2021-07-07 18:35 ` [PATCH Part2 RFC v4 14/40] crypto:ccp: Provide APIs to issue SEV-SNP commands Brijesh Singh
2021-07-08 18:56   ` Dr. David Alan Gilbert
2021-07-07 18:35 ` [PATCH Part2 RFC v4 15/40] crypto: ccp: Handle the legacy TMR allocation when SNP is enabled Brijesh Singh
2021-07-14 13:22   ` Marc Orr
2021-07-14 16:45     ` Brijesh Singh
2021-07-14 18:14       ` Marc Orr
2021-07-15 23:48   ` Sean Christopherson
2021-07-16 12:55     ` Brijesh Singh
2021-07-16 15:35       ` Sean Christopherson
2021-07-16 15:47         ` Brijesh Singh
2021-07-07 18:35 ` [PATCH Part2 RFC v4 16/40] crypto: ccp: Handle the legacy SEV command " Brijesh Singh
2021-07-07 18:35 ` [PATCH Part2 RFC v4 17/40] crypto: ccp: Add the SNP_PLATFORM_STATUS command Brijesh Singh
2021-07-07 18:35 ` [PATCH Part2 RFC v4 18/40] crypto: ccp: Add the SNP_{SET,GET}_EXT_CONFIG command Brijesh Singh
2021-07-07 18:35 ` [PATCH Part2 RFC v4 19/40] crypto: ccp: provide APIs to query extended attestation report Brijesh Singh
2021-07-07 18:35 ` [PATCH Part2 RFC v4 20/40] KVM: SVM: Make AVIC backing, VMSA and VMCB memory allocation SNP safe Brijesh Singh
2021-07-14 13:35   ` Marc Orr
2021-07-14 16:47     ` Brijesh Singh
2021-07-20 18:02   ` Sean Christopherson
2021-08-03 14:38     ` Brijesh Singh
2021-07-07 18:35 ` [PATCH Part2 RFC v4 21/40] KVM: SVM: Add initial SEV-SNP support Brijesh Singh
2021-07-16 18:00   ` Sean Christopherson
2021-07-16 18:46     ` Brijesh Singh
2021-07-16 19:31       ` Sean Christopherson
2021-07-16 21:03         ` Brijesh Singh
2021-07-07 18:35 ` [PATCH Part2 RFC v4 22/40] KVM: SVM: Add KVM_SNP_INIT command Brijesh Singh
2021-07-16 19:33   ` Sean Christopherson
2021-07-16 21:25     ` Brijesh Singh
2021-07-19 20:24       ` Sean Christopherson
2021-07-07 18:35 ` [PATCH Part2 RFC v4 23/40] KVM: SVM: Add KVM_SEV_SNP_LAUNCH_START command Brijesh Singh
2021-07-12 18:45   ` Peter Gonda
2021-07-16 19:43   ` Sean Christopherson
2021-07-16 21:42     ` Brijesh Singh
2021-07-07 18:36 ` [PATCH Part2 RFC v4 24/40] KVM: SVM: Add KVM_SEV_SNP_LAUNCH_UPDATE command Brijesh Singh
2021-07-16 20:01   ` Sean Christopherson
2021-07-16 22:00     ` Brijesh Singh
2021-07-19 20:51       ` Sean Christopherson
2021-07-19 21:34         ` Brijesh Singh
2021-07-19 21:36           ` Brijesh Singh
2021-07-07 18:36 ` [PATCH Part2 RFC v4 25/40] KVM: SVM: Reclaim the guest pages when SEV-SNP VM terminates Brijesh Singh
2021-07-16 20:09   ` Sean Christopherson
2021-07-16 22:16     ` Brijesh Singh
2021-07-17  0:46       ` Sean Christopherson
2021-07-19 12:55         ` Brijesh Singh
2021-07-19 17:18           ` Sean Christopherson
2021-07-19 18:34             ` Brijesh Singh
2021-07-19 19:03               ` Sean Christopherson
2021-07-19 19:14                 ` Sean Christopherson
2021-07-19 19:37                 ` Brijesh Singh
2021-07-20 16:40                   ` Sean Christopherson
2021-07-20 18:23                     ` Brijesh Singh
2021-07-07 18:36 ` [PATCH Part2 RFC v4 26/40] KVM: SVM: Add KVM_SEV_SNP_LAUNCH_FINISH command Brijesh Singh
2021-07-16 20:18   ` Sean Christopherson
2021-07-16 22:48     ` Brijesh Singh
2021-07-19 16:54       ` Sean Christopherson
2021-07-19 18:29         ` Brijesh Singh
2021-07-19 19:14           ` Sean Christopherson
2021-07-19 19:49             ` Brijesh Singh
2021-07-19 20:13               ` Sean Christopherson
2021-07-21 17:53         ` Marc Orr
2021-07-07 18:36 ` [PATCH Part2 RFC v4 27/40] KVM: X86: Add kvm_x86_ops to get the max page level for the TDP Brijesh Singh
2021-07-16 19:19   ` Sean Christopherson
2021-07-16 20:41     ` Brijesh Singh
2021-07-20 19:38       ` Sean Christopherson
2021-07-20 20:06         ` Brijesh Singh
2021-07-07 18:36 ` [PATCH Part2 RFC v4 28/40] KVM: X86: Introduce kvm_mmu_map_tdp_page() for use by SEV Brijesh Singh
2021-07-16 18:15   ` Sean Christopherson
2021-07-07 18:36 ` [PATCH Part2 RFC v4 29/40] KVM: X86: Introduce kvm_mmu_get_tdp_walk() for SEV-SNP use Brijesh Singh
2021-07-07 18:36 ` [PATCH Part2 RFC v4 30/40] KVM: X86: Define new RMP check related #NPF error bits Brijesh Singh
2021-07-16 20:22   ` Sean Christopherson
2021-07-17  0:34     ` Brijesh Singh
2021-07-07 18:36 ` [PATCH Part2 RFC v4 31/40] KVM: X86: update page-fault trace to log the 64-bit error code Brijesh Singh
2021-07-16 20:25   ` Sean Christopherson
2021-07-17  0:35     ` Brijesh Singh
2021-07-07 18:36 ` [PATCH Part2 RFC v4 32/40] KVM: SVM: Add support to handle GHCB GPA register VMGEXIT Brijesh Singh
2021-07-16 20:45   ` Sean Christopherson
2021-07-17  0:44     ` Brijesh Singh
2021-07-19 20:04       ` Sean Christopherson
2021-07-07 18:36 ` [PATCH Part2 RFC v4 33/40] KVM: SVM: Add support to handle MSR based Page State Change VMGEXIT Brijesh Singh
2021-07-16 21:00   ` Sean Christopherson
2021-07-19 14:19     ` Brijesh Singh
2021-07-19 18:55       ` Sean Christopherson
2021-07-19 19:15         ` Brijesh Singh
2021-08-13 16:32         ` Borislav Petkov
2021-07-07 18:36 ` [PATCH Part2 RFC v4 34/40] KVM: SVM: Add support to handle " Brijesh Singh
2021-07-16 21:14   ` Sean Christopherson
2021-07-19 14:24     ` Brijesh Singh
2021-07-07 18:36 ` [PATCH Part2 RFC v4 35/40] KVM: Add arch hooks to track the host write to guest memory Brijesh Singh
2021-07-19 23:30   ` Sean Christopherson
2021-07-20 15:15     ` Brijesh Singh
2021-07-07 18:36 ` [PATCH Part2 RFC v4 36/40] KVM: X86: Export the kvm_zap_gfn_range() for the SNP use Brijesh Singh
2021-07-07 18:36 ` [PATCH Part2 RFC v4 37/40] KVM: SVM: Add support to handle the RMP nested page fault Brijesh Singh
2021-07-20  0:10   ` Sean Christopherson
2021-07-20 17:55     ` Brijesh Singh
2021-07-20 22:31       ` Sean Christopherson
2021-07-20 23:53         ` Brijesh Singh
2021-07-21 20:15           ` Sean Christopherson
2021-07-07 18:36 ` [PATCH Part2 RFC v4 38/40] KVM: SVM: Provide support for SNP_GUEST_REQUEST NAE event Brijesh Singh
2021-07-19 22:50   ` Sean Christopherson [this message]
2021-07-20 14:37     ` Brijesh Singh
2021-07-20 16:28       ` Sean Christopherson
2021-07-20 18:21         ` Brijesh Singh
2021-07-20 22:09           ` Sean Christopherson
2021-07-07 18:36 ` [PATCH Part2 RFC v4 39/40] KVM: SVM: Use a VMSA physical address variable for populating VMCB Brijesh Singh
2021-07-21  0:20   ` Sean Christopherson
2021-07-21 16:26     ` Tom Lendacky
2021-07-07 18:36 ` [PATCH Part2 RFC v4 40/40] KVM: SVM: Support SEV-SNP AP Creation NAE event Brijesh Singh
2021-07-21  0:01   ` Sean Christopherson
2021-07-21 17:47     ` Tom Lendacky
2021-07-21 19:52       ` Sean Christopherson
2021-08-20 14:44         ` Tom Lendacky
2021-07-08 15:40 ` [PATCH Part2 RFC v4 00/40] Add AMD Secure Nested Paging (SEV-SNP) Hypervisor Support Dave Hansen

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