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 ..." 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 >
