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?
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
