On Thu, 2021-06-24 at 09:32 -0500, Tom Lendacky wrote: > On 6/24/21 5:38 AM, Paolo Bonzini wrote: > > On 24/06/21 10:20, Maxim Levitsky wrote: > > > Something else to note, just for our information is that KVM > > > these days does vmsave/vmload to VM_HSAVE_PA to store/restore > > > the additional host state, something that is frowned upon in the spec, > > > but there is some justification of doing this in the commit message, > > > citing an old spec which allowed this. > > > > True that. And there is no mention in the specification for VMRUN that > > the host state-save area is a subset of the VMCB format (i.e., that it > > uses VMCB offsets for whatever subset of the state it saves in the VMCB), > > so the spec reference in the commit message is incorrect. It would be > > nice if the spec guaranteed that. Michael, Tom? > > So that is (now) stated in APM volume 2, Appendix B in the paragraph after > Table B-3, where it starts "The format of the host save area is identical > to the guest save area described in the table below, except that ..." This is a very good find! I wish it was written in the commit message of commit that added that vmsave/vmload to VM_HSAVE_PA area. Maybe we should add a comment to the code pointing to this location of the APM. Thanks, Best regards, Maxim Levitsky > > Thanks, > Tom > > > In fact, Vitaly's patch *will* overwrite the vmsave/vmload parts of > > VM_HSAVE_PA, and it will store the L2 values rather than the L1 values, > > because KVM always does its vmload/vmrun/vmsave sequence using > > vmload(vmcs01) and vmsave(vmcs01)! So that has to be changed to use code > > similar to svm_set_nested_state (which can be moved to a separate function > > and reused): > > > > dest->es = src->es; > > dest->cs = src->cs; > > dest->ss = src->ss; > > dest->ds = src->ds; > > dest->gdtr = src->gdtr; > > dest->idtr = src->idtr; > > dest->rflags = src->rflags | X86_EFLAGS_FIXED; > > dest->efer = src->efer; > > dest->cr0 = src->cr0; > > dest->cr3 = src->cr3; > > dest->cr4 = src->cr4; > > dest->rax = src->rax; > > dest->rsp = src->rsp; > > dest->rip = src->rip; > > dest->cpl = 0; > > > > > > Paolo > >
