From: Sean Christopherson <seanjc@google.com>
To: Xin Li <xin@zytor.com>
Cc: kvm@vger.kernel.org, linux-kernel@vger.kernel.org,
linux-doc@vger.kernel.org, pbonzini@redhat.com, corbet@lwn.net,
tglx@linutronix.de, mingo@redhat.com, bp@alien8.de,
dave.hansen@linux.intel.com, x86@kernel.org, hpa@zytor.com,
luto@kernel.org, peterz@infradead.org,
andrew.cooper3@citrix.com
Subject: Re: [PATCH v3 24/27] KVM: nVMX: Add a prerequisite to existence of VMCS fields
Date: Tue, 25 Feb 2025 11:32:11 -0800 [thread overview]
Message-ID: <Z74au5wLvtFuJuS8@google.com> (raw)
In-Reply-To: <5b63fb37-bb1a-45f9-a6f9-58f6bf5b869e@zytor.com>
On Tue, Feb 25, 2025, Xin Li wrote:
> On 2/25/2025 8:22 AM, Sean Christopherson wrote:
> > On Mon, Sep 30, 2024, Xin Li (Intel) wrote:
> > > Add a prerequisite to existence of VMCS fields as some of them exist
> > > only on processors that support certain CPU features.
> > >
> > > This is required to fix KVM unit test VMX_VMCS_ENUM.MAX_INDEX.
> >
> > If making the KVM-Unit-Test pass is the driving force for this code, then NAK.
> > We looked at this in detail a few years back, and came to the conclusion that
> > trying to precisely track which fields are/aren't supported would likely do more
> > harm than good.
>
> I have to agree, it's no fun to track a VMCS field is added by which
> feature(s), and worst part is that one VMCS field could depend on 2+ totally
> irrelevant features, e.g., the secondary VM exit controls field exits on CPU
> that supports:
>
> 1) FRED
> 2) Prematurely busy shadow stack
>
> Thanks for making the ground rule clear.
>
> BTW, why don't we just remove this VMX_VMCS_ENUM.MAX_INDEX test?
Because it's still a valid test, albeit with caveats. KVM's (undocumented?) erratum
is that vmcs12 fields that are supported by KVM are always readable, but that's
mostly an orthogonal issuue to VMX_VMCS_ENUM.MAX_INDEX. I.e. KVM can and does
report a correct VMX_VMCS_ENUM.MAX_INDEX based on which VMCS fields KVM emulates.
The big caveat is that VMX_VMCS_ENUM.MAX_INDEX will be wrong if a VM is migrated
to a newer KVM and/or to a host with a superset of functionality. With those
caveats in mind, it's still nice to sanity check that KVM isn't advertising complete
garbage.
next prev parent reply other threads:[~2025-02-25 19:32 UTC|newest]
Thread overview: 81+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-10-01 5:00 [PATCH v3 00/27] Enable FRED with KVM VMX Xin Li (Intel)
2024-10-01 5:00 ` [PATCH v3 01/27] KVM: x86: Use a dedicated flow for queueing re-injected exceptions Xin Li (Intel)
2024-10-01 5:00 ` [PATCH v3 02/27] KVM: VMX: Don't modify guest XFD_ERR if CR0.TS=1 Xin Li (Intel)
2024-10-01 5:00 ` [PATCH v3 03/27] KVM: VMX: Add support for the secondary VM exit controls Xin Li (Intel)
2024-10-21 8:28 ` Chao Gao
2024-10-21 17:03 ` Xin Li
2024-10-22 2:47 ` Chao Gao
2024-10-22 16:30 ` Xin Li
2025-02-25 17:28 ` Sean Christopherson
2024-10-01 5:00 ` [PATCH v3 04/27] KVM: VMX: Initialize FRED VM entry/exit controls in vmcs_config Xin Li (Intel)
2024-10-01 5:00 ` [PATCH v3 05/27] KVM: VMX: Disable FRED if FRED consistency checks fail Xin Li (Intel)
2024-10-22 8:48 ` Chao Gao
2024-10-22 16:21 ` Xin Li
2024-11-26 15:32 ` Borislav Petkov
2024-11-26 18:53 ` Xin Li
2024-11-26 19:04 ` Borislav Petkov
2024-10-01 5:00 ` [PATCH v3 06/27] x86/cea: Export per CPU variable cea_exception_stacks Xin Li (Intel)
2024-10-01 16:12 ` Dave Hansen
2024-10-01 17:51 ` Xin Li
2024-10-01 18:18 ` Dave Hansen
2024-10-01 5:00 ` [PATCH v3 07/27] KVM: VMX: Initialize VMCS FRED fields Xin Li (Intel)
2024-10-22 9:06 ` Chao Gao
2024-10-22 16:18 ` Xin Li
2024-10-01 5:00 ` [PATCH v3 08/27] KVM: x86: Use KVM-governed feature framework to track "FRED enabled" Xin Li (Intel)
2024-10-01 5:00 ` [PATCH v3 09/27] KVM: VMX: Do not use MAX_POSSIBLE_PASSTHROUGH_MSRS in array definition Xin Li (Intel)
2024-11-26 18:02 ` Borislav Petkov
2024-11-26 19:22 ` Xin Li
2024-11-26 20:06 ` Borislav Petkov
2024-11-27 6:46 ` Xin Li
2024-11-27 6:55 ` Borislav Petkov
2024-11-27 7:02 ` Xin Li
2024-11-27 7:10 ` Borislav Petkov
2024-11-27 7:32 ` Xin Li
2024-11-27 7:58 ` Borislav Petkov
2024-10-01 5:00 ` [PATCH v3 10/27] KVM: VMX: Set FRED MSR interception Xin Li (Intel)
2024-11-13 11:31 ` Chao Gao
2024-10-01 5:00 ` [PATCH v3 11/27] KVM: VMX: Save/restore guest FRED RSP0 Xin Li (Intel)
2024-10-01 5:00 ` [PATCH v3 12/27] KVM: VMX: Add support for FRED context save/restore Xin Li (Intel)
2024-10-01 5:00 ` [PATCH v3 13/27] KVM: x86: Add a helper to detect if FRED is enabled for a vCPU Xin Li (Intel)
2024-10-01 5:00 ` [PATCH v3 14/27] KVM: VMX: Pass XFD_ERR as pseudo-payload when injecting #NM Xin Li (Intel)
2024-10-01 5:00 ` [PATCH v3 15/27] KVM: VMX: Virtualize FRED event_data Xin Li (Intel)
2024-10-01 5:00 ` [PATCH v3 16/27] KVM: VMX: Virtualize FRED nested exception tracking Xin Li (Intel)
2024-10-24 6:24 ` Chao Gao
2024-10-25 8:04 ` Xin Li
2024-10-28 6:33 ` Chao Gao
2024-12-05 7:16 ` Xin Li
2024-10-01 5:01 ` [PATCH v3 17/27] KVM: x86: Mark CR4.FRED as not reserved when guest can use FRED Xin Li (Intel)
2024-10-24 7:18 ` Chao Gao
2024-12-12 18:48 ` Xin Li
2024-12-12 19:05 ` Sean Christopherson
2024-12-13 18:43 ` Xin Li
2024-10-01 5:01 ` [PATCH v3 18/27] KVM: VMX: Dump FRED context in dump_vmcs() Xin Li (Intel)
2024-10-24 7:23 ` Chao Gao
2024-10-24 16:50 ` Xin Li
2024-10-01 5:01 ` [PATCH v3 19/27] KVM: x86: Allow FRED/LKGS to be advertised to guests Xin Li (Intel)
2024-10-01 5:01 ` [PATCH v3 20/27] KVM: x86: Allow WRMSRNS " Xin Li (Intel)
2025-02-25 15:41 ` Sean Christopherson
2024-10-01 5:01 ` [PATCH v3 21/27] KVM: VMX: Invoke vmx_set_cpu_caps() before nested setup Xin Li (Intel)
2024-10-24 7:49 ` Chao Gao
2024-10-25 7:34 ` Xin Li
2025-02-25 16:01 ` Sean Christopherson
2024-10-01 5:01 ` [PATCH v3 22/27] KVM: nVMX: Add support for the secondary VM exit controls Xin Li (Intel)
2024-10-01 5:01 ` [PATCH v3 23/27] KVM: nVMX: Add a prerequisite to SHADOW_FIELD_R[OW] macros Xin Li (Intel)
2024-10-01 5:01 ` [PATCH v3 24/27] KVM: nVMX: Add a prerequisite to existence of VMCS fields Xin Li (Intel)
2025-02-25 16:22 ` Sean Christopherson
2025-02-25 16:37 ` Xin Li
2025-02-25 19:32 ` Sean Christopherson [this message]
2024-10-01 5:01 ` [PATCH v3 25/27] KVM: nVMX: Add FRED " Xin Li (Intel)
2024-10-24 7:42 ` Chao Gao
2024-10-25 7:25 ` Xin Li
2024-10-28 9:07 ` Chao Gao
2024-10-28 18:27 ` Sean Christopherson
2024-10-29 17:40 ` Xin Li
2024-10-01 5:01 ` [PATCH v3 26/27] KVM: nVMX: Add VMCS FRED states checking Xin Li (Intel)
2024-10-01 5:01 ` [PATCH v3 27/27] KVM: nVMX: Allow VMX FRED controls Xin Li (Intel)
2025-02-19 0:26 ` [PATCH v3 00/27] Enable FRED with KVM VMX Xin Li
2025-02-25 15:24 ` Sean Christopherson
2025-02-25 17:04 ` Xin Li
2025-02-25 17:35 ` Sean Christopherson
2025-02-25 18:48 ` Xin Li
2025-02-28 17:06 ` Sean Christopherson
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