Re: [PATCH v5 11/15] KVM: nVMX: Set UMIP bit CR4_FIXED1 MSR when emulating UMIP

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

 



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



[Index of Archives]     [KVM ARM]     [KVM ia64]     [KVM ppc]     [Virtualization Tools]     [Spice Development]     [Libvirt]     [Libvirt Users]     [Linux USB Devel]     [Linux Audio Users]     [Yosemite Questions]     [Linux Kernel]     [Linux SCSI]     [XFree86]

  Powered by Linux