On 2014-07-07 12:38, Alok Kataria wrote: > From: Jim Mattson <[email protected]> > > We have noticed that qemu-kvm hangs early in the BIOS when runnning nested > under some versions of VMware ESXi. > > The problem we believe is because KVM assumes that the platform preserves > the 'G' but for any segment register. The SVM specification itemizes the > segment attribute bits that are observed by the CPU, but the (G)ranularity bit > is not one of the bits itemized, for any segment. Though current AMD CPUs keep > track of the (G)ranularity bit for all segment registers other than CS, the > specification does not require it. VMware's virtual CPU may not track the > (G)ranularity bit for any segment register. > > Since kvm already synthesizes the (G)ranularity bit for the CS segment. It > should do so for all segments. The patch below does that, and helps get rid of > the hangs. Patch applies on top of Linus' tree. > > Signed-off-by: Jim Mattson <[email protected]> > Signed-off-by: Alok N Kataria <[email protected]> > > Index: linux-2.6/arch/x86/kvm/svm.c > =================================================================== > --- linux-2.6.orig/arch/x86/kvm/svm.c 2014-07-07 15:32:52.724368183 +0530 > +++ linux-2.6/arch/x86/kvm/svm.c 2014-07-07 15:34:19.664748841 +0530 > @@ -1415,7 +1415,7 @@ > var->avl = (s->attrib >> SVM_SELECTOR_AVL_SHIFT) & 1; > var->l = (s->attrib >> SVM_SELECTOR_L_SHIFT) & 1; > var->db = (s->attrib >> SVM_SELECTOR_DB_SHIFT) & 1; > - var->g = (s->attrib >> SVM_SELECTOR_G_SHIFT) & 1; > + var->g = s->limit > 0xfffff; > > /* > * AMD's VMCB does not have an explicit unusable field, so emulate it > @@ -1424,14 +1424,6 @@ > var->unusable = !var->present || (var->type == 0); > > switch (seg) { > - case VCPU_SREG_CS: > - /* > - * SVM always stores 0 for the 'G' bit in the CS selector in > - * the VMCB on a VMEXIT. This hurts cross-vendor migration: > - * Intel's VMENTRY has a check on the 'G' bit. > - */ > - var->g = s->limit > 0xfffff; > - break; > case VCPU_SREG_TR: > /* > * Work around a bug where the busy flag in the tr selector > >
Thanks for pushing this. I already tried to analyze the spec in this regard in [1]. But even if it turns out we could read the bit on real HW, I think this patch is fine in order to be compatible with ESXi. Jan [1] http://thread.gmane.org/gmane.comp.emulators.kvm.devel/124252 -- Siemens AG, Corporate Technology, CT RTC ITP SES-DE Corporate Competence Center Embedded Linux -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html
