linux-kernel - Re: [PATCH v2 0/9] Move initializing SEV/SNP functionality to KVM

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Message-ID: <57d43fae-ab5e-4686-9fed-82cd3c0e0a3c@amd.com>
Date: Tue, 17 Dec 2024 17:16:01 -0600
From: "Kalra, Ashish" <ashish.kalra@....com>
To: Sean Christopherson <seanjc@...gle.com>
Cc: Dionna Amalie Glaze <dionnaglaze@...gle.com>, pbonzini@...hat.com,
 tglx@...utronix.de, mingo@...hat.com, bp@...en8.de,
 dave.hansen@...ux.intel.com, x86@...nel.org, hpa@...or.com,
 thomas.lendacky@....com, john.allen@....com, herbert@...dor.apana.org.au,
 davem@...emloft.net, michael.roth@....com, kvm@...r.kernel.org,
 linux-kernel@...r.kernel.org, linux-crypto@...r.kernel.org,
 linux-coco@...ts.linux.dev
Subject: Re: [PATCH v2 0/9] Move initializing SEV/SNP functionality to KVM



On 12/17/2024 3:37 PM, Sean Christopherson wrote:
> On Tue, Dec 17, 2024, Ashish Kalra wrote:
>>
>>
>> On 12/17/2024 10:00 AM, Dionna Amalie Glaze wrote:
>>> On Mon, Dec 16, 2024 at 3:57 PM Ashish Kalra <Ashish.Kalra@....com> wrote:
>>>>
>>>> From: Ashish Kalra <ashish.kalra@....com>
>>>
>>>> The on-demand SEV initialization support requires a fix in QEMU to
>>>> remove check for SEV initialization to be done prior to launching
>>>> SEV/SEV-ES VMs.
>>>> NOTE: With the above fix for QEMU, older QEMU versions will be broken
>>>> with respect to launching SEV/SEV-ES VMs with the newer kernel/KVM as
>>>> older QEMU versions require SEV initialization to be done before
>>>> launching SEV/SEV-ES VMs.
>>>>
>>>
>>> I don't think this is okay. I think you need to introduce a KVM
>>> capability to switch over to the new way of initializing SEV VMs and
>>> deprecate the old way so it doesn't need to be supported for any new
>>> additions to the interface.
>>>
>>
>> But that means KVM will need to support both mechanisms of doing SEV
>> initialization - during KVM module load time and the deferred/lazy
>> (on-demand) SEV INIT during VM launch.
> 
> What's the QEMU change?  Dionna is right, we can't break userspace, but maybe
> there's an alternative to supporting both models.

Here is the QEMU fix : (makes a SEV PLATFORM STATUS firmware call via PSP driver ioctl
to check if SEV is in INIT state)
 
diff --git a/target/i386/sev.c b/target/i386/sev.c
index 1a4eb1ada6..4fa8665395 100644
--- a/target/i386/sev.c
+++ b/target/i386/sev.c
@@ -1503,15 +1503,6 @@ static int sev_common_kvm_init(ConfidentialGuestSupport *cgs, Error **errp)
         }
     }

-    if (sev_es_enabled() && !sev_snp_enabled()) {
-        if (!(status.flags & SEV_STATUS_FLAGS_CONFIG_ES)) {
-            error_setg(errp, "%s: guest policy requires SEV-ES, but "
-                         "host SEV-ES support unavailable",
-                         __func__);
-            return -1;
-        }
-    }
-
     trace_kvm_sev_init();
     switch (x86_klass->kvm_type(X86_CONFIDENTIAL_GUEST(sev_common))) {
     case KVM_X86_DEFAULT_VM: