Re: [PATCH] KVM: x86: Don't attempt to load PDPTRs when 64-bit mode is enabled

[Sean Christopherson]

On Mon, Jul 13, 2020 at 06:57:32PM -0700, Sean Christopherson wrote:
> Don't attempt to load PDPTRs if EFER.LME=1, i.e. if 64-bit mode is
> enabled.  A recent change to reload the PDTPRs when CR0.CD or CR0.NW is
> toggled botched the EFER.LME handling and sends KVM down the PDTPR path
> when is_paging() is true, i.e. when the guest toggles CD/NW in 64-bit
> mode.
> 
> Split the CR0 checks for 64-bit vs. 32-bit PAE into separate paths.  The
> 64-bit path is specifically checking state when paging is toggled on,
> i.e. CR0.PG transititions from 0->1.  The PDPTR path now needs to run if
> the new CR0 state has paging enabled, irrespective of whether paging was
> already enabled.  Trying to shave a few cycles to make the PDPTR path an
> "else if" case is a mess.
> 
> Fixes: d42e3fae6faed ("kvm: x86: Read PDPTEs on CR0.CD and CR0.NW changes")
> Cc: Jim Mattson <jmattson@xxxxxxxxxx>
> Cc: Oliver Upton <oupton@xxxxxxxxxx>
> Cc: Peter Shier <pshier@xxxxxxxxxx>
> Signed-off-by: Sean Christopherson <sean.j.christopherson@xxxxxxxxx>
> ---

Ping.  This really needs to be in the initial pull for 5.9, as is kvm/queue
has a 100% fatality rate for me.