From: Michael Roth <michael.roth@amd.com>
To: Sean Christopherson <seanjc@google.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>,
<srinivas.pandruvada@linux.intel.com>, <rientjes@google.com>,
<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>,
Brijesh Singh <brijesh.singh@amd.com>
Subject: Re: [PATCH v14 09/22] KVM: SEV: Add support to handle MSR based Page State Change VMGEXIT
Date: Thu, 25 Apr 2024 17:00:08 -0500 [thread overview]
Message-ID: <20240425220008.boxnurujlxbx62pg@amd.com> (raw)
In-Reply-To: <ZilyxFnJvaWUJOkc@google.com>
On Wed, Apr 24, 2024 at 01:59:48PM -0700, Sean Christopherson wrote:
> On Sun, Apr 21, 2024, Michael Roth wrote:
> > +static int snp_begin_psc_msr(struct kvm_vcpu *vcpu, u64 ghcb_msr)
> > +{
> > + u64 gpa = gfn_to_gpa(GHCB_MSR_PSC_REQ_TO_GFN(ghcb_msr));
> > + u8 op = GHCB_MSR_PSC_REQ_TO_OP(ghcb_msr);
> > + struct vcpu_svm *svm = to_svm(vcpu);
> > +
> > + if (op != SNP_PAGE_STATE_PRIVATE && op != SNP_PAGE_STATE_SHARED) {
> > + set_ghcb_msr(svm, GHCB_MSR_PSC_RESP_ERROR);
> > + return 1; /* resume guest */
> > + }
> > +
> > + vcpu->run->exit_reason = KVM_EXIT_VMGEXIT;
> > + vcpu->run->vmgexit.type = KVM_USER_VMGEXIT_PSC_MSR;
> > + vcpu->run->vmgexit.psc_msr.gpa = gpa;
> > + vcpu->run->vmgexit.psc_msr.op = op;
>
> Argh, no.
>
> This is the same crud that TDX tried to push[*]. Use KVM's existing user exits,
> and extend as *needed*. There is no good reason page state change requests need
> *two* exit reasons. The *only* thing KVM supports right now is private<=>shared
> conversions, and that can be handled with either KVM_HC_MAP_GPA_RANGE or
> KVM_EXIT_MEMORY_FAULT.
>
> The non-MSR flavor can batch requests, but I'm willing to bet that the overwhelming
> majority of requests are contiguous, i.e. can be combined into a range by KVM,
> and that handling any outliers by performing multiple exits to userspace will
> provide sufficient performance.
That does tend to be the case. We won't have as much granularity with
the per-entry error codes, but KVM_SET_MEMORY_ATTRIBUTES would be
expected to be for the entire range anyway, and if that fails for
whatever reason then we KVM_BUG_ON() anyway. We do have to have handling
for cases where the entries aren't contiguous however, which would
involve multiple KVM_EXIT_HYPERCALLs until everything is satisfied. But
not a huge deal since it doesn't seem to be a common case.
KVM_HC_MAP_GPA_RANGE seems like a nice option because we'd also have the
flexibility to just issue that directly within a guest rather than
relying on SNP/TDX specific hcalls. I don't know if that approach is
practical for a real guest, but it could be useful for having re-usable
guest code in KVM selftests that "just works" for all variants of
SNP/TDX/sw-protected. (though we'd still want stuff that exercises
SNP/TDX->KVM_HC_MAP_GPA_RANGE translation).
I think we'd there is some potential baggage there with the previous SEV
live migration use cases. There's some potential that existing guest kernels
will use it once it gets advertised and issue them alongside GHCB-based
page-state changes. It might make sense to use one of the reserved bits
to denote this flavor of KVM_HC_MAP_GPA_RANGE as being for
hardware/software-protected VMs and not interchangeable with calls that
were used for SEV live migration stuff.
If this seems reasonable I'll give it a go and see what it looks like.
>
> And the non-MSR version that comes in later patch is a complete mess. It kicks
> the PSC out to userspace without *any* validation. As I complained in the TDX
> thread, that will create an unmaintable ABI for KVM.
>
> KVM needs to have its own, well-defined ABI. Splitting functionality between
> KVM and userspace at seemingly random points is not maintainable.
>
> E.g. if/when KVM supports UNSMASH, upgrading to the KVM would arguably break
> userspace as PSC requests that previously exited would suddenly be handled by
> KVM. Maybe. It's impossible to review this because there's no KVM ABI, KVM is
> little more than a dumb pipe parroting information to userspace.
It leans on the GHCB spec to avoid re-inventing structs/documentation
for things like Page State Change buffers, but do have some control
as we want over how much we farm out versus lock into the KVM ABI. For
instance the accompanying Documentation/ update mentions we only send a
subset of GHCB requests that need to be handled by userspace, so we
could handle SMASH/UNSMASH in KVM without breaking expectations (or if
SMASH/UNSMASH were intermixed with PSCs, documentation that only PSC
opcodes could be updated by userspace).
But I'm certainly not arguing it wouldn't be better to have a
guest-agnostic alternative if we can reach an agreement on that, and
KVM_HC_MAP_GPA_RANGE seems like it could work.
-Mike
>
> I truly do not understand why we would even consider allowing this. We push back
> on people wanting new hypercalls for some specific use case, because we already
> have generic ways to achieve things, but then CoCo comes along and we apparently
> throw out any thought of maintainability. I don't get it.
>
> [*] https://lore.kernel.org/all/Zg18ul8Q4PGQMWam@google.com
next prev parent reply other threads:[~2024-04-25 22:00 UTC|newest]
Thread overview: 56+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-04-21 18:01 [PATCH v14 00/22] Add AMD Secure Nested Paging (SEV-SNP) Hypervisor Support Michael Roth
2024-04-21 18:01 ` [PATCH v14 01/22] KVM: SEV: Select KVM_GENERIC_PRIVATE_MEM when CONFIG_KVM_AMD_SEV=y Michael Roth
2024-04-21 18:01 ` [PATCH v14 02/22] KVM: SEV: Add support to handle AP reset MSR protocol Michael Roth
2024-04-21 18:01 ` [PATCH v14 03/22] KVM: SEV: Add GHCB handling for Hypervisor Feature Support requests Michael Roth
2024-04-24 20:21 ` Sean Christopherson
2024-04-25 20:52 ` Michael Roth
2024-04-25 21:55 ` Sean Christopherson
2024-04-21 18:01 ` [PATCH v14 04/22] KVM: SEV: Add initial SEV-SNP support Michael Roth
2024-04-21 18:01 ` [PATCH v14 05/22] KVM: SEV: Add KVM_SEV_SNP_LAUNCH_START command Michael Roth
2024-04-24 23:26 ` Sean Christopherson
2024-04-21 18:01 ` [PATCH v14 06/22] KVM: SEV: Add KVM_SEV_SNP_LAUNCH_UPDATE command Michael Roth
2024-04-24 23:58 ` Sean Christopherson
2024-04-21 18:01 ` [PATCH v14 07/22] KVM: SEV: Add KVM_SEV_SNP_LAUNCH_FINISH command Michael Roth
2024-04-21 18:01 ` [PATCH v14 08/22] KVM: SEV: Add support to handle GHCB GPA register VMGEXIT Michael Roth
2024-04-21 18:01 ` [PATCH v14 09/22] KVM: SEV: Add support to handle MSR based Page State Change VMGEXIT Michael Roth
2024-04-24 20:59 ` Sean Christopherson
2024-04-25 22:00 ` Michael Roth [this message]
2024-04-25 22:13 ` Sean Christopherson
2024-04-26 17:16 ` Michael Roth
2024-04-26 20:14 ` Sean Christopherson
2024-04-26 22:24 ` Michael Roth
2024-04-26 22:48 ` Michael Roth
2024-04-21 18:01 ` [PATCH v14 10/22] KVM: SEV: Add support to handle " Michael Roth
2024-04-21 18:01 ` [PATCH v14 11/22] KVM: SEV: Add support to handle RMP nested page faults Michael Roth
2024-04-21 18:01 ` [PATCH v14 12/22] KVM: SEV: Support SEV-SNP AP Creation NAE event Michael Roth
2024-04-21 18:01 ` [PATCH v14 13/22] KVM: SEV: Add support for GHCB-based termination requests Michael Roth
2024-04-21 18:01 ` [PATCH v14 14/22] KVM: SEV: Implement gmem hook for initializing private pages Michael Roth
2024-04-21 18:01 ` [PATCH v14 15/22] KVM: SEV: Implement gmem hook for invalidating " Michael Roth
2024-04-21 18:01 ` [PATCH v14 16/22] KVM: x86: Implement gmem hook for determining max NPT mapping level Michael Roth
2024-04-25 0:45 ` Sean Christopherson
2024-04-21 18:01 ` [PATCH v14 17/22] KVM: SEV: Avoid WBINVD for HVA-based MMU notifications for SNP Michael Roth
2024-04-25 0:17 ` Sean Christopherson
2024-04-21 18:01 ` [PATCH v14 18/22] KVM: SVM: Add module parameter to enable SEV-SNP Michael Roth
2024-04-21 18:01 ` [PATCH v14 19/22] KVM: SEV: Provide support for SNP_GUEST_REQUEST NAE event Michael Roth
2024-04-21 18:01 ` [PATCH v14 20/22] crypto: ccp: Add the SNP_VLEK_LOAD command Michael Roth
2024-04-21 18:01 ` [PATCH v14 21/22] crypto: ccp: Add the SNP_{PAUSE,RESUME}_ATTESTATION commands Michael Roth
2024-04-25 0:15 ` Sean Christopherson
2024-04-26 17:35 ` Michael Roth
2024-04-26 19:57 ` Sean Christopherson
2024-04-26 21:46 ` Michael Roth
2024-04-27 0:10 ` Sean Christopherson
2024-04-27 1:32 ` Michael Roth
2024-04-29 14:27 ` Sean Christopherson
2024-04-21 18:01 ` [PATCH v14 22/22] KVM: SEV: Provide support for SNP_EXTENDED_GUEST_REQUEST NAE event Michael Roth
2024-04-25 0:10 ` Sean Christopherson
2024-04-26 17:57 ` Michael Roth
2024-04-23 16:21 ` [PATCH v14 23/22] [SQUASH] KVM: SEV: Add support to handle GHCB GPA register VMGEXIT Michael Roth
2024-04-23 16:21 ` [PATCH v14 24/22] [SQUASH] KVM: SEV: Add support to handle MSR based Page State Change VMGEXIT Michael Roth
2024-04-23 16:21 ` [PATCH v14 25/22] [SQUASH] KVM: SEV: Add support to handle " Michael Roth
2024-04-23 16:21 ` [PATCH v14 26/22] [SQUASH] KVM: SEV: Add support for GHCB-based termination requests Michael Roth
2024-04-23 16:21 ` [PATCH v14 27/22] [SQUASH] KVM: SEV: Provide support for SNP_GUEST_REQUEST NAE event Michael Roth
2024-04-23 16:21 ` [PATCH v14 28/22] [SQUASH] KVM: SEV: Provide support for SNP_EXTENDED_GUEST_REQUEST " Michael Roth
2024-04-23 21:36 ` Jarkko Sakkinen
2024-04-23 16:21 ` [PATCH v14 29/22] [SQUASH] KVM: SEV: Support SEV-SNP AP Creation " Michael Roth
2024-04-23 16:31 ` [PATCH v14 00/22] Add AMD Secure Nested Paging (SEV-SNP) Hypervisor Support Michael Roth
2024-04-24 16:51 ` Paolo Bonzini
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20240425220008.boxnurujlxbx62pg@amd.com \
--to=michael.roth@amd.com \
--cc=ak@linux.intel.com \
--cc=alpergun@google.com \
--cc=ardb@kernel.org \
--cc=ashish.kalra@amd.com \
--cc=bp@alien8.de \
--cc=brijesh.singh@amd.com \
--cc=dave.hansen@linux.intel.com \
--cc=dovmurik@linux.ibm.com \
--cc=hpa@zytor.com \
--cc=jarkko@kernel.org \
--cc=jmattson@google.com \
--cc=jroedel@suse.de \
--cc=kirill@shutemov.name \
--cc=kvm@vger.kernel.org \
--cc=liam.merwick@oracle.com \
--cc=linux-coco@lists.linux.dev \
--cc=linux-crypto@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-mm@kvack.org \
--cc=luto@kernel.org \
--cc=mingo@redhat.com \
--cc=nikunj.dadhania@amd.com \
--cc=pankaj.gupta@amd.com \
--cc=pbonzini@redhat.com \
--cc=peterz@infradead.org \
--cc=pgonda@google.com \
--cc=rientjes@google.com \
--cc=sathyanarayanan.kuppuswamy@linux.intel.com \
--cc=seanjc@google.com \
--cc=slp@redhat.com \
--cc=srinivas.pandruvada@linux.intel.com \
--cc=tglx@linutronix.de \
--cc=thomas.lendacky@amd.com \
--cc=tobin@ibm.com \
--cc=tony.luck@intel.com \
--cc=vbabka@suse.cz \
--cc=vkuznets@redhat.com \
--cc=x86@kernel.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for read-only IMAP folder(s) and NNTP newsgroup(s).