Re: [Xen-devel] [PATCH 4/5] libxc/pvh: set default MTRR type to write-back

[Wei Liu <wei.liu2@xxxxxxxxxx>]

On Mon, May 14, 2018 at 05:42:53PM +0100, Wei Liu wrote:
> On Mon, May 14, 2018 at 05:02:47PM +0100, Roger Pau Monné wrote:
> > On Mon, May 14, 2018 at 05:00:51PM +0100, Wei Liu wrote:
> > > On Thu, May 10, 2018 at 06:15:04PM +0100, Roger Pau Monne wrote:
> > > > @@ -1014,6 +1034,30 @@ static int vcpu_hvm(struct xc_dom_image *dom)
> > > >      if ( dom->start_info_seg.pfn )
> > > >          bsp_ctx.cpu.rbx = dom->start_info_seg.pfn << PAGE_SHIFT;
> > > >  
> > > > +    /* Set the MTRR. */
> > > > +    bsp_ctx.mtrr_d.typecode = HVM_SAVE_CODE(MTRR);
> > > > +    bsp_ctx.mtrr_d.instance = 0;
> > > > +    bsp_ctx.mtrr_d.length = HVM_SAVE_LENGTH(MTRR);
> > > > +
> > > > +    mtrr_record = hvm_get_save_record(full_ctx, HVM_SAVE_CODE(MTRR), 
> > > > 0);
> > > > +    if ( !mtrr_record )
> > > > +    {
> > > > +        xc_dom_panic(dom->xch, XC_INTERNAL_ERROR,
> > > > +                     "%s: unable to get MTRR save record", __func__);
> > > > +        goto out;
> > > > +    }
> > > 
> > > Will this break cross version migration when the older hypervisor
> > > doesn't have such record?
> > 
> > This migration record is already present, it's not introduced in this
> > patch series. I'm simply making use of it in order to set a valid
> > initial MTRR state.
> > 
> 
> Then I'm even more confused: does this mean the record is not properly
> honoured in the hypervisor? I.e. this is a hypervisor bug?
> 

Or maybe this means the setting of the default type should happen
somewhere else? Let me read all the code to make sure I'm not talking
nonsense and misguide you here.

Wei.

_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxxxxxxxxx
https://lists.xenproject.org/mailman/listinfo/xen-devel