Messages in this thread | | | Subject | Re: [PATCH] KVM: x86: Allow guest to set EFER.NX=1 on non-PAE 32-bit kernels | From | Paolo Bonzini <> | Date | Fri, 6 Aug 2021 13:58:00 +0200 |
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On 05/08/21 20:38, Sean Christopherson wrote: > Fast forward to today, and KVM has long since stopped running the guest > with the host's EFER.NX. Not only does KVM context switch EFER if > host.EFER.NX=1 && guest.EFER.NX=0, KVM also forces host.EFER.NX=0 && > guest.EFER.NX=1 when using shadow paging (to emulate SMEP). Furthermore, > the entire motivation for the restriction was made obsolete over a decade > ago when Intel added dedicated host and guest EFER fields in the VMCS > (Nehalem timeframe), which reduced the overhead of context switching EFER > from 400+ cycles (2 * WRMSR + 1 * RDMSR) to a mere ~2 cycles.
Both pretty good points. :) Queued, thanks.
Paolo
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