On Thu, Jul 14, 2016 at 1:33 AM, Paolo Bonzini <pbonzini@xxxxxxxxxx> wrote: > > > 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. Good catch, I agree they can be removed. > > Of course this would just be a small simplification, so I'm applying the > patch as is to kvm/next. SGTM. Thanks for the review. > > 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
