Re: [Xen-devel] [PATCH v4 7/8] libxc/pvh: set default MTRR type to write-back

[Roger Pau Monné <roger.pau@xxxxxxxxxx>]

On Wed, Sep 26, 2018 at 01:29:27PM +0100, Andrew Cooper wrote:
> On 08/06/18 10:59, 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;
> > +    }
> > +
> > +    memcpy(&bsp_ctx.mtrr, mtrr_record, sizeof(bsp_ctx.mtrr));
> > +
> > +    /* TODO: maybe this should be a firmware option instead? */
> > +    if ( !dom->device_model )
> > +        /*
> > +         * Enable MTRR, set default type to WB.
> > +         * TODO: add MMIO areas as UC when passthrough is supported.
> > +         */
> > +        bsp_ctx.mtrr.msr_mtrr_def_type = MTRR_TYPE_WRBACK |
> > +                                         MTRR_DEF_TYPE_ENABLE;
> 
> This is buggy.  MTRRs are per-vcpu and expected to match.  This only
> works by chance in the HVM case because all settings are still 0 at this
> point.

Yes, I will look into it ASAP, but I'm not sure if the current
save/restore trick that's done here will be possible with vcpus that
are down or I will need to expand the save/restore logic to allow
setting the state of vcpus that are down.

Thanks, Roger.

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