Re: [PATCH 1/2] KVM: MMU: fix ept=0/pte.u=0/pte.w=0/CR0.WP=0/CR4.SMEP=1/EFER.NX=0 combo

From: Xiao Guangrong
Date: Thu Mar 10 2016 - 03:46:48 EST

On 03/08/2016 07:44 PM, Paolo Bonzini wrote:
Yes, all of these are needed. :) This is admittedly a bit odd, but
kvm-unit-tests access.flat tests this if you run it with "-cpu host"
and of course ept=0.

KVM handles supervisor writes of a pte.u=0/pte.w=0/CR0.WP=0 page by
setting U=0 and W=1 in the shadow PTE. This will cause a user write
to fault and a supervisor write to succeed (which is correct because
CR0.WP=0). A user read instead will flip U=0 to 1 and W=1 back to 0.

BTW, it should be pte.u = 1 where you mentioned above.