Re: [Xen-devel] [PATCH v4.1] libxc: Defer initialization of start_page for HVM guests

[Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>]

On 01/08/2016 04:56 AM, Ian Campbell wrote:
> On Thu, 2016-01-07 at 17:11 -0500, Boris Ostrovsky wrote:
> > With commit 8c45adec18e0 ("libxc: create unmapped initrd in domain
> > builder if supported") location of ramdisk may not be available to
> > HVMlite guests by the time alloc_magic_pages_hvm() is invoked if the
> > guest supports unmapped initrd.
> >
> > So let's move ramdisk info initialization (along with a few other
> > operations that are not directly related to allocating magic/special
> > pages) from alloc_magic_pages_hvm() to bootlate_hvm().
> The "few other operations" are just the hvm_info init for standard HVM by
> this iteration?
For HVM yes, but we also move command string initialization for HVMlite.

> > --- a/tools/libxc/include/xc_dom.h
> > +++ b/tools/libxc/include/xc_dom.h
> > @@ -71,6 +71,7 @@ struct xc_dom_image {
> >   
> >       /* arguments and parameters */
> >       char *cmdline;
> > +    size_t cmdline_size;
> Perhaps /* Including NULL and padding/alignment */ ?
>
> (That's the sort of thing I don't mind doing on commit if there is
> agreement and no other changes required)
Yes, please add this (unless you want to see v5, v5.1 and v5.2)

> > @@ -1095,8 +1044,8 @@ static int vcpu_hvm(struct xc_dom_image *dom)
> >       /* Set the IP. */
> >       bsp_ctx.cpu.rip = dom->parms.phys_entry;
> >   
> > -    if ( dom->start_info_pfn )
> > -        bsp_ctx.cpu.rbx = dom->start_info_pfn << PAGE_SHIFT;
> > +    if ( dom->start_info_seg.pfn )
> > +        bsp_ctx.cpu.rbx = dom->start_info_seg.pfn << PAGE_SHIFT;
> Just to check: dom->start_info_pfn is unused/nil in the regular-hvm case,
> correct (i.e. this code is dm-list specific both before and after)?
Yes, start_info_pfn is only used by PV(H) and since the structure is 
memset to zero during allocation the 'if' clause is only executed for 
HVMlite.
> > +    else
> > +    {
> > +        void *hvm_info_page;
> > +
> > +        if ( (hvm_info_page = xc_map_foreign_range(
> > +                  xch, domid, PAGE_SIZE, PROT_READ | PROT_WRITE,
> > +                  HVM_INFO_PFN)) == NULL )
> > +            return -1;
> > +        build_hvm_info(hvm_info_page, dom);
> > +        munmap(hvm_info_page, PAGE_SIZE);
> > +    }
> Did you test regular HVM guests after this movement?
Yes, I did.

-boris

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