Re: [Xen-devel] [PATCH v4.2] libxc: Defer initialization of start_page for HVM guests

[Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>]

On 01/08/2016 09:30 AM, Juergen Gross wrote:
> On 08/01/16 15:19, Boris Ostrovsky wrote:
> > On 01/07/2016 11:57 PM, Juergen Gross wrote:
> > > On 07/01/16 23:19, 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().
> > > >
> > > > Since we now split allocation and mapping of the start_info segment
> > > > let's stash it, along with cmdline length, in xc_dom_image so that we
> > > > can check whether we are mapping correctly-sized range.
> > > >
> > > > We can also stop using xc_dom_image.start_info_pfn and leave it for
> > > > PV(H) guests only.
> > > >
> > > > Signed-off-by: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
> > > > ---
> > > > v4:
> > > >    * See the last two paragraphs from commit message above
> > > >
> > > > v4.1:
> > > >    * Inverted testing of start_info_size in bootlate_hvm().
> > > >
> > > > v4.2
> > > >    * <facepalm> Actually do what I said I'd do in 4.1
> > > >
> > > >    tools/libxc/include/xc_dom.h |    2 +
> > > >    tools/libxc/xc_dom_x86.c     |  140
> > > > +++++++++++++++++++++++------------------
> > > >    2 files changed, 80 insertions(+), 62 deletions(-)
> > > >
> > > > diff --git a/tools/libxc/include/xc_dom.h b/tools/libxc/include/xc_dom.h
> > > > index 2460818..cac4698 100644
> > > > --- 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;
> > > >        uint32_t f_requested[XENFEAT_NR_SUBMAPS];
> > > >          /* info from (elf) kernel image */
> > > > @@ -91,6 +92,7 @@ struct xc_dom_image {
> > > >        struct xc_dom_seg p2m_seg;
> > > >        struct xc_dom_seg pgtables_seg;
> > > >        struct xc_dom_seg devicetree_seg;
> > > > +    struct xc_dom_seg start_info_seg; /* HVMlite only */
> > > Instead of adding HVM specific members here, you could make use of
> > > dom.arch_private and use just a local structure defined in xc_dom_x86.c.
> > I did consider this but since we already keep type-specific segments in
> > this structure (e.g. p2m_seg) decided to add an explicit segment for
> > HVMlite.
> But p2m_seg is accessed from multiple sources, while cmdline_size and
> start_info_seg would be local to xc_dom_x86.c
>
> BTW: thanks for the hint - I'll have a look whether p2m_seg can't be
> moved to arch_private...
>
> > Besides, I think to properly use it we'd need to add an arch hook and
> > IMHO it's not worth the trouble in this case.
> Why would you need another arch hook? Just add the arch_private_size
> member to struct xc_dom_arch and everything is set up for you. Look
> how it is handled for the pv case in xc_dom_x86.c
So it is already hooked up, I didn't notice that we do register 
xc_hvm_32, even though arch_private_size is 0.
This would be a type-specific area though, not arch-specific as the name 
implies. So perhaps xc_dom_image_x86 should be modified to include 
type-specific structures (via a union).
-boris


_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxx
http://lists.xen.org/xen-devel