Re: [Xen-devel] new domain builder breaks compatibility

[Gerd Hoffmann <kraxel@xxxxxxx>]

Keir Fraser wrote:
> On 2/2/07 07:59, "Gerd Hoffmann" <kraxel@xxxxxxx> wrote:
> 
>>> I'll handle this and update xen.h.
>> Restoring the 4MB alignment is easy too, see attached patch (which also
>> fixes the 4MB alignment for virt_base).
> 
> I suppose it is nice to stick with the guarantees described in xen.h, since
> it is so easy to do so.

Slightly updated version of the patch, the previous one did fixup
virt_base too late.  This one should work in theory.  It's not really
tested though, the VIRT_BASE specified by linux kernels is at a 4MB
border anyway, so the fixup is a no-op ...

cheers,
  Gerd

-- 
Gerd Hoffmann <kraxel@xxxxxxx>

---
 tools/libxc/xc_dom_core.c |    3 +++
 tools/libxc/xc_dom_x86.c  |    4 +++-
 2 files changed, 6 insertions(+), 1 deletion(-)

Index: build-32-unstable-13788/tools/libxc/xc_dom_x86.c
===================================================================
--- build-32-unstable-13788.orig/tools/libxc/xc_dom_x86.c
+++ build-32-unstable-13788/tools/libxc/xc_dom_x86.c
@@ -66,11 +66,12 @@ static int count_pgtables(struct xc_dom_
 
     extra_pages = dom->alloc_bootstack ? 1 : 0;
     extra_pages += dom->extra_pages;
+    extra_pages += 128; /* 512kB padding */
     pages = extra_pages;
     for (;;)
     {
        try_virt_end = round_up(dom->virt_alloc_end + pages * PAGE_SIZE_X86,
-                               bits_to_mask(l1_bits));
+                               bits_to_mask(22)); /* 4MB alignment */
        dom->pg_l4 =
            nr_page_tables(dom->parms.virt_base, try_virt_end, l4_bits);
        dom->pg_l3 =
@@ -313,6 +314,7 @@ static int alloc_magic_pages(struct xc_d
     if (xc_dom_feature_translated(dom))
        dom->shared_info_pfn = xc_dom_alloc_page(dom, "shared info");
     dom->alloc_bootstack = 1;
+
     return 0;
 }
 
Index: build-32-unstable-13788/tools/libxc/xc_dom_core.c
===================================================================
--- build-32-unstable-13788.orig/tools/libxc/xc_dom_core.c
+++ build-32-unstable-13788/tools/libxc/xc_dom_core.c
@@ -717,6 +717,9 @@ int xc_dom_build_image(struct xc_dom_ima
     }
     page_size = XC_DOM_PAGE_SIZE(dom);
 
+    /* 4MB align virtual base address */
+    dom->parms.virt_base &= ~(((uint64_t)1<<22)-1);
+
     /* load kernel */
     if (0 != xc_dom_alloc_segment(dom, &dom->kernel_seg, "kernel",
                                  dom->kernel_seg.vstart,

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