On 14/07/2016 02:16, David Matlack wrote: > KVM maintains L1's current VMCS in guest memory, at the guest physical > page identified by the argument to VMPTRLD. This makes hairy > time-of-check to time-of-use bugs possible,as VCPUs can be writing > the the VMCS page in memory while KVM is emulating VMLAUNCH and > VMRESUME. > > The spec documents that writing to the VMCS page while it is loaded is > "undefined". Therefore it is reasonable to load the entire VMCS into > an internal cache during VMPTRLD and ignore writes to the VMCS page > -- the guest should be using VMREAD and VMWRITE to access the current > VMCS. > > To adhere to the spec, KVM should flush the current VMCS during VMPTRLD, > and the target VMCS during VMCLEAR (as given by the operand to VMCLEAR). > Since this implementation of VMCS caching only maintains the the current > VMCS, VMCLEAR will only do a flush if the operand to VMCLEAR is the > current VMCS pointer. > > KVM will also flush during VMXOFF, which is not mandated by the spec, > but also not in conflict with the spec. > > Signed-off-by: David Matlack <dmatlack@xxxxxxxxxx> This is a good change. There is another change that is possible on top: with this change you don't need current_vmcs12/current_vmcs12_page at all, I think. You can just use current_vmptr and kvm_read/write_guest to write back the VMCS12, possibly the cached variants. Of course this would just be a small simplification, so I'm applying the patch as is to kvm/next. Thanks, Paolo -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
