From: Paolo Bonzini <pbonzini@redhat.com>
To: Sean Christopherson <seanjc@google.com>
Cc: Vitaly Kuznetsov <vkuznets@redhat.com>,
Wanpeng Li <wanpengli@tencent.com>,
Jim Mattson <jmattson@google.com>, Joerg Roedel <joro@8bytes.org>,
kvm@vger.kernel.org, linux-kernel@vger.kernel.org,
Eric Li <ercli@ucdavis.edu>, David Matlack <dmatlack@google.com>,
Oliver Upton <oupton@google.com>
Subject: Re: [PATCH v5 11/15] KVM: nVMX: Set UMIP bit CR4_FIXED1 MSR when emulating UMIP
Date: Fri, 22 Jul 2022 11:49:25 +0200 [thread overview]
Message-ID: <40500f56-5ea4-f0c3-2a75-290ed20c9c81@redhat.com> (raw)
In-Reply-To: <20220607213604.3346000-12-seanjc@google.com>
On 6/7/22 23:36, Sean Christopherson wrote:
> Make UMIP an "allowed-1" bit CR4_FIXED1 MSR when KVM is emulating UMIP.
> KVM emulates UMIP for both L1 and L2, and so should enumerate that L2 is
> allowed to have CR4.UMIP=1. Not setting the bit doesn't immediately
> break nVMX, as KVM does set/clear the bit in CR4_FIXED1 in response to a
> guest CPUID update, i.e. KVM will correctly (dis)allow nested VM-Entry
> based on whether or not UMIP is exposed to L1.
>
> That said, KVM should enumerate the bit as being allowed from time zero,
> e.g. userspace will see the wrong value if the MSR is read before CPUID
> is written. And a future patch will quirk KVM's behavior of stuffing
> CR4_FIXED1 in response to guest CPUID changes, as CR4_FIXED1 is not
> strictly required to match the CPUID model exposed to L1.
I'm not sure about this; there's no *practical* need to allow it, since
there is generally a 1:n mapping between CPUID and CR4 reserved bits.
Do you mind removing the "future patch" reference from the commit message?
Paolo
next prev parent reply other threads:[~2022-07-22 9:50 UTC|newest]
Thread overview: 31+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-06-07 21:35 [PATCH v5 00/15] KVM: nVMX: VMX MSR quirk+fixes, CR4 fixes Sean Christopherson
2022-06-07 21:35 ` [PATCH v5 01/15] KVM: x86: Split kvm_is_valid_cr4() and export only the non-vendor bits Sean Christopherson
2022-06-07 21:35 ` [PATCH v5 02/15] KVM: nVMX: Account for KVM reserved CR4 bits in consistency checks Sean Christopherson
2022-06-07 21:35 ` [PATCH v5 03/15] KVM: nVMX: Inject #UD if VMXON is attempted with incompatible CR0/CR4 Sean Christopherson
2022-06-07 21:35 ` [PATCH v5 04/15] KVM: nVMX: Rename handle_vm{on,off}() to handle_vmx{on,off}() Sean Christopherson
2022-06-07 21:35 ` [PATCH v5 05/15] KVM: nVMX: Let userspace set nVMX MSR to any _host_ supported value Sean Christopherson
2022-10-31 16:39 ` Yu Zhang
2022-10-31 17:11 ` Sean Christopherson
2022-11-01 10:18 ` Yu Zhang
2022-11-01 17:58 ` Sean Christopherson
2022-11-02 8:54 ` Yu Zhang
2022-11-03 16:53 ` Sean Christopherson
2022-11-07 8:28 ` Yu Zhang
2022-11-07 15:06 ` Sean Christopherson
2022-11-08 10:21 ` Yu Zhang
2022-11-08 18:35 ` Sean Christopherson
2022-11-10 8:44 ` Yu Zhang
2022-11-10 16:08 ` Sean Christopherson
2022-06-07 21:35 ` [PATCH v5 06/15] KVM: nVMX: Keep KVM updates to BNDCFGS ctrl bits across MSR write Sean Christopherson
2022-07-22 9:06 ` Paolo Bonzini
2022-06-07 21:35 ` [PATCH v5 07/15] KVM: VMX: Add helper to check if the guest PMU has PERF_GLOBAL_CTRL Sean Christopherson
2022-06-07 21:35 ` [PATCH v5 08/15] KVM: nVMX: Keep KVM updates to PERF_GLOBAL_CTRL ctrl bits across MSR write Sean Christopherson
2022-06-07 21:35 ` [PATCH v5 09/15] KVM: nVMX: Drop nested_vmx_pmu_refresh() Sean Christopherson
2022-06-07 21:35 ` [PATCH v5 10/15] KVM: nVMX: Add a quirk for KVM tweaks to VMX MSRs Sean Christopherson
2022-06-07 21:36 ` [PATCH v5 11/15] KVM: nVMX: Set UMIP bit CR4_FIXED1 MSR when emulating UMIP Sean Christopherson
2022-07-22 9:49 ` Paolo Bonzini [this message]
2022-06-07 21:36 ` [PATCH v5 12/15] KVM: nVMX: Extend VMX MSRs quirk to CR0/4 fixed1 bits Sean Christopherson
2022-07-22 9:50 ` Paolo Bonzini
2022-06-07 21:36 ` [PATCH v5 13/15] KVM: selftests: Add test to verify KVM's VMX MSRs quirk for controls Sean Christopherson
2022-06-07 21:36 ` [PATCH v5 14/15] KVM: selftests: Extend VMX MSRs test to cover CR4_FIXED1 (and its quirks) Sean Christopherson
2022-06-07 21:36 ` [PATCH v5 15/15] KVM: selftests: Verify VMX MSRs can be restored to KVM-supported values Sean Christopherson
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