Re: [Xen-devel] [PATCH v5 09/11] xen: add capability to load initrd outside of initial mapping

[Daniel Kiper <daniel.kiper@xxxxxxxxxx>]

On Mon, Feb 29, 2016 at 09:27:42AM +0100, Juergen Gross wrote:
> On 26/02/16 16:41, Daniel Kiper wrote:
> > On Fri, Feb 26, 2016 at 03:28:21PM +0100, Juergen Gross wrote:
> >> On 26/02/16 15:00, Daniel Kiper wrote:
> >>> On Thu, Feb 25, 2016 at 04:33:46PM +0100, Juergen Gross wrote:
> >>>> On 25/02/16 13:47, Daniel Kiper wrote:
> >>>>> On Thu, Feb 25, 2016 at 12:33:35PM +0100, Juergen Gross wrote:
> >>>>>> Modern pvops linux kernels support an initrd not covered by the initial
> >>>>>> mapping. This capability is flagged by an elf-note.
> >>>>>>
> >>>>>> In case the elf-note is set by the kernel don't place the initrd into
> >>>>>> the initial mapping. This will allow to load larger initrds and/or
> >>>>>> support domains with larger memory, as the initial mapping is limited
> >>>>>> to 2GB and it is containing the p2m list.
> >>>>>>
> >>>>>> Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
> >>>>>> ---
> >>>>>> V5: let call grub_xen_alloc_final() all subfunctions unconditionally
> >>>>>>     and let them decide whether they need to do anything
> >>>>>> V4: rename grub_xen_alloc_end() to grub_xen_alloc_final()
> >>>>>> ---
> >>>>>>  grub-core/loader/i386/xen.c        | 65 
> >>>>>> ++++++++++++++++++++++++++++++--------
> >>>>>>  grub-core/loader/i386/xen_fileXX.c |  3 ++
> >>>>>>  include/grub/xen_file.h            |  1 +
> >>>>>>  3 files changed, 56 insertions(+), 13 deletions(-)
> >>>>>>
> >>>>>> diff --git a/grub-core/loader/i386/xen.c b/grub-core/loader/i386/xen.c
> >>>>>> index 2e12763..466f0c0 100644
> >>>>>> --- a/grub-core/loader/i386/xen.c
> >>>>>> +++ b/grub-core/loader/i386/xen.c
> >>>>>> @@ -228,6 +228,9 @@ grub_xen_p2m_alloc (void)
> >>>>>>    grub_size_t p2msize;
> >>>>>>    grub_err_t err;
> >>>>>>
> >>>>>> +  if (xen_state.virt_mfn_list)
> >>>>>> +    return GRUB_ERR_NONE;
> >>>>>> +
> >>>>>>    xen_state.state.mfn_list = xen_state.max_addr;
> >>>>>>    xen_state.next_start.mfn_list =
> >>>>>>      xen_state.max_addr + xen_state.xen_inf.virt_base;
> >>>>>> @@ -250,6 +253,9 @@ grub_xen_special_alloc (void)
> >>>>>>    grub_relocator_chunk_t ch;
> >>>>>>    grub_err_t err;
> >>>>>>
> >>>>>> +  if (xen_state.virt_start_info)
> >>>>>> +    return GRUB_ERR_NONE;
> >>>>>> +
> >>>>>>    err = grub_relocator_alloc_chunk_addr (xen_state.relocator, &ch,
> >>>>>>                                         xen_state.max_addr,
> >>>>>>                                         sizeof (xen_state.next_start));
> >>>>>> @@ -281,6 +287,9 @@ grub_xen_pt_alloc (void)
> >>>>>>    grub_uint64_t nr_info_pages;
> >>>>>>    grub_uint64_t nr_pages, nr_pt_pages, nr_need_pages;
> >>>>>>
> >>>>>> +  if (xen_state.virt_pgtable)
> >>>>>> +    return GRUB_ERR_NONE;
> >>>>>> +
> >>>>>>    xen_state.next_start.pt_base =
> >>>>>>      xen_state.max_addr + xen_state.xen_inf.virt_base;
> >>>>>>    xen_state.state.paging_start = xen_state.max_addr >> PAGE_SHIFT;
> >>>>>> @@ -320,6 +329,24 @@ grub_xen_pt_alloc (void)
> >>>>>>  }
> >>>>>>
> >>>>>>  static grub_err_t
> >>>>>> +grub_xen_alloc_final (void)
> >>>>>> +{
> >>>>>> +  grub_err_t err;
> >>>>>> +
> >>>>>> +  err = grub_xen_p2m_alloc ();
> >>>>>> +  if (err)
> >>>>>> +    return err;
> >>>>>> +  err = grub_xen_special_alloc ();
> >>>>>> +  if (err)
> >>>>>> +    return err;
> >>>>>> +  err = grub_xen_pt_alloc ();
> >>>>>> +  if (err)
> >>>>>> +    return err;
> >>>>>
> >>>>> Could you move grub_xen_p2m_alloc() here? This way 
> >>>>> grub_xen_alloc_final()
> >>>>> will be real final in patch 11 and you do not need an extra condition
> >>>>> around grub_xen_p2m_alloc().
> >>>>
> >>>> No. Page tables must be allocated after p2m unless p2m is outside of
> >>>> initial kernel mapping (patch 11).
> >>>
> >>> OK, I was afraid of that. However, then grub_xen_alloc_final() is not 
> >>> final.
> >>
> >> Sure it is. Patch 11 just adds allocation to grub_xen_alloc_final(), not
> >> after it.
> >
> > Excerpt from patch 11:
> >
> > @@ -474,6 +503,12 @@ grub_xen_boot (void)
> >    err = grub_xen_alloc_final ();
> >    if (err)
> >      return err;
> > +  if (xen_state.xen_inf.has_p2m_base)
> > +    {
> > +      err = grub_xen_p2m_alloc ();
> > +      if (err)
> > +        return err;
> > +    }
> >
>
> Hmph. No idea what I looked at when writing my previous reply.
>
> >>> So, maybe it should be called grub_xen_alloc_boot_data() or something 
> >>> like that.
> >
> > Then my previous comment is still valid.
>
> What about naming it grub_xen_alloc_kernel_mapping() ? This is what it
> really does: It is allocating all not yet allocated areas which are to
> be included in the initial kernel mapping.

This function does three things:
  - allocate memory for p2m array,
  - allocate special pages (e.g. console),
  - allocate memory for page tables.

Three of them are part of boot data described by struct start_info.
Well, there are also other required stuff to properly boot PV guest.
So, I can agree that grub_xen_alloc_boot_data() is not perfect but
I cannot find anything better. Additionally, IMO grub_xen_alloc_kernel_mapping()
is not right choice too. It suggests that this functions does anything
with kernel mapping. Yep, it does, however, this is only one third
of this function. So, I tend to use my proposal or anything better
which is short and quite well describes what is going in this
function as whole.

Daniel

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