From: Sean Christopherson <seanjc@google.com>
To: Michael Roth <michael.roth@amd.com>
Cc: kvm@vger.kernel.org, linux-coco@lists.linux.dev,
linux-mm@kvack.org, linux-crypto@vger.kernel.org,
x86@kernel.org, linux-kernel@vger.kernel.org,
tglx@linutronix.de, mingo@redhat.com, jroedel@suse.de,
thomas.lendacky@amd.com, hpa@zytor.com, ardb@kernel.org,
pbonzini@redhat.com, vkuznets@redhat.com, jmattson@google.com,
luto@kernel.org, dave.hansen@linux.intel.com, slp@redhat.com,
pgonda@google.com, peterz@infradead.org,
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dovmurik@linux.ibm.com, tobin@ibm.com, bp@alien8.de,
vbabka@suse.cz, kirill@shutemov.name, ak@linux.intel.com,
tony.luck@intel.com, sathyanarayanan.kuppuswamy@linux.intel.com,
alpergun@google.com, jarkko@kernel.org, ashish.kalra@amd.com,
nikunj.dadhania@amd.com, pankaj.gupta@amd.com,
liam.merwick@oracle.com
Subject: Re: [PATCH v15 19/20] KVM: SEV: Provide support for SNP_EXTENDED_GUEST_REQUEST NAE event
Date: Tue, 14 May 2024 07:36:20 -0700 [thread overview]
Message-ID: <ZkN25BPuLtTUmDKk@google.com> (raw)
In-Reply-To: <20240514025115.dkw3ysqrdbfaa2sg@amd.com>
On Mon, May 13, 2024, Michael Roth wrote:
> On Mon, May 13, 2024 at 04:48:25PM -0700, Sean Christopherson wrote:
> > Actually, I take that back, this isn't even an optimization, it's literally a
> > non-generic implementation of kvm_run.immediate_exit.
>
> Relying on a generic -EINTR response resulting from kvm_run.immediate_exit
> doesn't seem like a very robust way to ensure the attestation request
> was made to firmware. It seems fully possible that future code changes
> could result in EINTR being returned for other reasons. So how do you
> reliably detect that the EINTR is a result of immediate_exit being called
> after the attestation request is made to firmware? We could squirrel something
> away in struct kvm_run to probe for, but delivering another
> KVM_EXIT_SNP_REQ_CERT with an extra flag set seems to be reasonably
> userspace-friendly.
And unnecessarily specific to a single exit. But it's a non-issue (except
possibly on ARM).
I doubt it's formally documented anywhere, but userspace absolutely relies on
kvm_run.immediate_exit to be processed _after_ complete_userspace_io(). If KVM
exits with -EINTR before invoking cui(), live migration will break due to taking
a snapshot of vCPU state in the middle of an instruction.
Given that userspace has likely built up rigid expectations for immediate_exit,
I don't see any problem formally documenting KVM's behavior, i.e. signing a
contract guaranteeing that KVM will complete the "back half" of emulation if
immediate_exit is set and KVM_RUN return -EINTR.
ARM is the only arch that is at all suspect, due to its rather massive
kvm_arch_vcpu_run_pid_change() hook. At a quick glance, it seems to be ok, too.
And if it's not, we need to fix that asap, because it's like a bug waiting to
happen.
> > If this were an optimization, i.e. KVM truly notified userspace without exiting,
> > then it would need to be a lot more robust, e.g. to ensure userspace actually
> > received the notification before KVM moved on.
>
> Right, this does rely on exiting via , not userspace polling for flags or
> anything along that line.
>
> >
> > > + __u8 flags;
> > > + #define KVM_USER_VMGEXIT_REQ_CERTS_STATUS_PENDING 0
> > > + #define KVM_USER_VMGEXIT_REQ_CERTS_STATUS_DONE 1
> >
> > This is also a weird reimplementation of generic functionality. KVM nullifies
> > vcpu->arch.complete_userspace_io _before_ invoking the callback. So if a callback
> > needs to run again on the next KVM_RUN, it can simply set complete_userspace_io
> > again. In other words, literally doing nothing will get you what you want :-)
>
> We could just have the completion callback set complete_userspace_io
> again, but then you'd always get 2 userspace exit events per attestation
> request. There could be some userspaces that don't implement the
> file-locking scheme, in which case they wouldn't need the 2nd notification.
Then they don't set immediate_exit.
> That's why the KVM_USER_VMGEXIT_REQ_CERTS_FLAGS_NOTIFY_DONE flag is provided
> as an opt-in.
>
> The pending/done status bits are so userspace can distinguish between the
> start of a certificate request and the completion side of it after it gets
> bound a completed attestation request and the filelock can be released.
next prev parent reply other threads:[~2024-05-14 14:36 UTC|newest]
Thread overview: 64+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-05-01 8:51 [PATCH v15 00/20] Add AMD Secure Nested Paging (SEV-SNP) Hypervisor Support Michael Roth
2024-05-01 8:51 ` [PATCH v15 01/20] Revert "KVM: x86: Add gmem hook for determining max NPT mapping level" Michael Roth
2024-05-01 8:51 ` [PATCH v15 02/20] KVM: x86: Add hook for determining max NPT mapping level Michael Roth
2024-05-02 23:11 ` Isaku Yamahata
2024-05-07 17:48 ` Paolo Bonzini
2024-05-01 8:51 ` [PATCH v15 03/20] KVM: SEV: Select KVM_GENERIC_PRIVATE_MEM when CONFIG_KVM_AMD_SEV=y Michael Roth
2024-05-01 8:51 ` [PATCH v15 04/20] KVM: SEV: Add initial SEV-SNP support Michael Roth
2024-05-01 8:51 ` [PATCH v15 05/20] KVM: SEV: Add KVM_SEV_SNP_LAUNCH_START command Michael Roth
2024-05-01 8:51 ` [PATCH v15 06/20] KVM: SEV: Add KVM_SEV_SNP_LAUNCH_UPDATE command Michael Roth
2024-05-01 8:51 ` [PATCH v15 07/20] KVM: SEV: Add KVM_SEV_SNP_LAUNCH_FINISH command Michael Roth
2024-05-01 8:51 ` [PATCH v15 08/20] KVM: SEV: Add support to handle GHCB GPA register VMGEXIT Michael Roth
2024-05-01 8:51 ` [PATCH v15 09/20] KVM: SEV: Add support to handle MSR based Page State Change VMGEXIT Michael Roth
2024-05-16 8:28 ` Binbin Wu
2024-05-16 17:23 ` Paolo Bonzini
2024-05-21 0:49 ` Binbin Wu
2024-05-21 21:49 ` Michael Roth
2024-05-27 12:25 ` Binbin Wu
2024-05-28 10:39 ` Paolo Bonzini
2024-05-29 20:02 ` Sean Christopherson
2024-05-31 1:22 ` Binbin Wu
2024-05-31 13:10 ` Paolo Bonzini
2024-05-30 16:47 ` Zhi Wang
2024-05-01 8:52 ` [PATCH v15 10/20] KVM: SEV: Add support to handle " Michael Roth
2024-05-01 8:52 ` [PATCH v15 11/20] KVM: SEV: Add support to handle RMP nested page faults Michael Roth
2024-05-01 8:52 ` [PATCH v15 12/20] KVM: SEV: Support SEV-SNP AP Creation NAE event Michael Roth
2024-05-01 8:52 ` [PATCH v15 13/20] KVM: SEV: Implement gmem hook for initializing private pages Michael Roth
2024-05-20 10:16 ` Huang, Kai
2024-05-20 17:35 ` Sean Christopherson
2024-05-20 21:57 ` Huang, Kai
2024-05-20 23:15 ` Sean Christopherson
2024-05-20 23:41 ` Huang, Kai
2024-05-21 0:30 ` Sean Christopherson
2024-05-20 19:14 ` Isaku Yamahata
2024-05-01 8:52 ` [PATCH v15 14/20] KVM: SEV: Implement gmem hook for invalidating " Michael Roth
2024-05-01 8:52 ` [PATCH v15 15/20] KVM: x86: Implement hook for determining max NPT mapping level Michael Roth
2024-05-01 8:52 ` [PATCH v15 16/20] KVM: SEV: Avoid WBINVD for HVA-based MMU notifications for SNP Michael Roth
2024-05-01 8:52 ` [PATCH v15 17/20] KVM: SVM: Add module parameter to enable SEV-SNP Michael Roth
2024-05-01 8:52 ` [PATCH v15 18/20] KVM: SEV: Provide support for SNP_GUEST_REQUEST NAE event Michael Roth
2024-05-01 8:52 ` [PATCH v15 19/20] KVM: SEV: Provide support for SNP_EXTENDED_GUEST_REQUEST " Michael Roth
2024-05-13 23:48 ` Sean Christopherson
2024-05-14 2:51 ` Michael Roth
2024-05-14 14:36 ` Sean Christopherson [this message]
2024-05-15 1:25 ` [PATCH] KVM: SEV: Replace KVM_EXIT_VMGEXIT with KVM_EXIT_SNP_REQ_CERTS Michael Roth
2024-05-01 8:52 ` [PATCH v15 20/20] crypto: ccp: Add the SNP_VLEK_LOAD command Michael Roth
2024-05-07 18:04 ` [PATCH v15 00/20] Add AMD Secure Nested Paging (SEV-SNP) Hypervisor Support Paolo Bonzini
2024-05-07 18:14 ` Michael Roth
2024-05-10 2:34 ` Michael Roth
2024-05-10 1:58 ` [PATCH v15 21/23] KVM: MMU: Disable fast path for private memslots Michael Roth
2024-05-10 1:58 ` [PATCH v15 22/23] KVM: SEV: Fix return code interpretation for RMP nested page faults Michael Roth
2024-05-10 13:58 ` Sean Christopherson
2024-05-10 15:36 ` Michael Roth
2024-05-10 16:01 ` Paolo Bonzini
2024-05-10 16:37 ` Michael Roth
2024-05-10 16:59 ` Paolo Bonzini
2024-05-10 17:25 ` Paolo Bonzini
2024-05-14 8:10 ` Borislav Petkov
2024-05-10 1:58 ` [PATCH v15 23/23] KVM: SEV: Fix PSC handling for SMASH/UNSMASH and partial update ops Michael Roth
2024-05-10 17:09 ` Paolo Bonzini
2024-05-10 19:08 ` Michael Roth
2024-05-10 13:47 ` [PATCH v15 21/23] KVM: MMU: Disable fast path for private memslots Sean Christopherson
2024-05-10 13:50 ` Paolo Bonzini
2024-05-10 15:27 ` Michael Roth
2024-05-10 15:59 ` Sean Christopherson
2024-05-10 17:47 ` Isaku Yamahata
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