Re: [Xen-devel] [PATCH v4 09/11] xen: add capability to load initrd outside of initial mapping

[Daniel Kiper <daniel.kiper@xxxxxxxxxx>]

On Mon, Feb 22, 2016 at 10:18:38AM +0100, Juergen Gross wrote:
> On 22/02/16 09:42, Daniel Kiper wrote:
> > On Mon, Feb 22, 2016 at 07:03:17AM +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>
> >> Reviewed-by: Daniel Kiper <daniel.kiper@xxxxxxxxxx>
> >> ---
> >> V4: rename grub_xen_alloc_end() to grub_xen_alloc_final()
> >> ---
> >>  grub-core/loader/i386/xen.c        | 61 
> >> ++++++++++++++++++++++++++++++--------
> >>  grub-core/loader/i386/xen_fileXX.c |  3 ++
> >>  include/grub/xen_file.h            |  1 +
> >>  3 files changed, 52 insertions(+), 13 deletions(-)
> >>
> >> diff --git a/grub-core/loader/i386/xen.c b/grub-core/loader/i386/xen.c
> >> index 2e12763..22a94ae 100644
> >> --- a/grub-core/loader/i386/xen.c
> >> +++ b/grub-core/loader/i386/xen.c
> >> @@ -58,6 +58,7 @@ struct xen_loader_state {
> >>    grub_uint64_t modules_target_start;
> >>    grub_size_t n_modules;
> >>    int loaded;
> >> +  int alloc_end_called;
> >
> > alloc_end_called -> alloc_final_called
> >
> >>  };
> >>
> >>  static struct xen_loader_state xen_state;
> >> @@ -320,6 +321,28 @@ grub_xen_pt_alloc (void)
> >>  }
> >>
> >>  static grub_err_t
> >> +grub_xen_alloc_final (void)
> >> +{
> >> +  grub_err_t err;
> >> +
> >> +  if (xen_state.alloc_end_called)
> >> +    return GRUB_ERR_NONE;
> >> +  xen_state.alloc_end_called = 1;
> >
> > This is not nice. What happens if grub_xen_p2m_alloc() allocate what
> > is needed and grub_xen_special_alloc() fails?
>
> Then grub_xen_alloc_final will fail resulting in boot failure of the
> new kernel. The memory allocated by the single functions will be freed
> in case a new boot is attempted (patch 1 and 2).
>
> > Maybe grub_xen_p2m_alloc(), grub_xen_special_alloc() and grub_xen_pt_alloc()
> > should check itself that required regions are allocated properly
> > (if (something != NULL)) and do nothing if yes.
>
> Hmm, with grub_xen_reset() doing appropriate cleanups this would be an
> option. I think I'll change it as you are suggesting.

It looks that we can completely avoid that stuff. I think that
grub_xen_alloc_final() should be called conditionally in both
places/cases. That is all.

Daniel

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