On 10/02/2015 02:59 PM, Ian Campbell wrote:
On Fri, 2015-10-02 at 07:49 +0200, Juergen Gross wrote:
In case the kernel of a new pv-domU indicates it is supporting an
unmapped initrd, don't waste precious virtual space for the initrd,
but allocate only guest physical memory for it.
Signed-off-by: Juergen Gross <jgr...@suse.com>
---
tools/libxc/xc_dom_core.c | 22 ++++++++++++++++++++--
1 file changed, 20 insertions(+), 2 deletions(-)
diff --git a/tools/libxc/xc_dom_core.c b/tools/libxc/xc_dom_core.c
index b510bbd..85b531a 100644
--- a/tools/libxc/xc_dom_core.c
+++ b/tools/libxc/xc_dom_core.c
@@ -1019,8 +1019,9 @@ int xc_dom_build_image(struct xc_dom_image *dom)
if ( dom->kernel_loader->loader(dom) != 0 )
goto err;
- /* load ramdisk */
- if ( dom->ramdisk_blob )
+ /* Load ramdisk if initial mapping required. */
+ if ( dom->ramdisk_blob &&
+ (!dom->parms.mod_start_pfn || dom->ramdisk_seg.vstart) )
{
if ( xc_dom_build_ramdisk(dom) != 0 )
goto err;
@@ -1063,6 +1064,23 @@ int xc_dom_build_image(struct xc_dom_image *dom)
__FUNCTION__, dom->virt_alloc_end);
DOMPRINTF("%-20s: virt_pgtab_end : 0x%" PRIx64 "",
__FUNCTION__, dom->virt_pgtab_end);
+
+ /* Prepare allocating unmapped memory. */
+ if ( dom->virt_pgtab_end )
+ dom->virt_alloc_end = dom->virt_pgtab_end;
+
+ /* Load ramdisk if no initial mapping required. */
+ if ( dom->ramdisk_blob && !dom->ramdisk_seg.vstart &&
+ dom->parms.mod_start_pfn )
+ {
+ if ( xc_dom_build_ramdisk(dom) != 0 )
+ goto err;
+ dom->flags |= SIF_MOD_START_PFN;
+ dom->ramdisk_seg.vend = dom->ramdisk_seg.vend -
dom->ramdisk_seg.vstart;
+ dom->ramdisk_seg.vstart = dom->ramdisk_seg.pfn;
+ dom->ramdisk_seg.vend += dom->ramdisk_seg.vstart;
This seems like it is trying to do something clever, like partially
reversing something which the xc_dom_alloc_segment call in
xc_dom_build_ramdisk has done.
It's just changing the boundaries of the initrd to fit the interface
for it being not mapped (indicated by the SIF_MOD_START_PFN flag).
It looks like the vend handling in particular is just a complicated way of
subtracting vstart and adding pfn, with the aim of rebasing from virt to
phys world.
Hmm, not more complicated as:
len = dom->ramdisk_seg.vend - dom->ramdisk_seg.vstart;
dom->ramdisk_seg.vstart = dom->ramdisk_seg.pfn;
dom->ramdisk_seg.vend = dom->ramdisk_seg.pfn + len;
I have to admit that above variant might be easier to understand. :-)
Plus vstart/end are addresses, while presumably pfn is a page number, so
I'm confused about that as well.
The naming is irritating, yes. I think I'll change this when I'm
modifying the allocation interface (see my answer to patch 5).
I'm also not clear how/where the virtual mapping is avoided, given that
this code here does strictly more than the original code above which is now
made conditional does.
The page tables are built before. So they don't cover the initrd memory.
Juergen
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