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

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>
  * See the last two paragraphs from commit message above

  * Inverted testing of start_info_size in bootlate_hvm().

  * <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.

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.


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