[Xen-devel] [RFC PATCH v3 01/22] x86/setup: Don't skip 2MiB underneath relocated Xen image

[David Woodhouse <dwmw2@infradead.org>]

From: David Woodhouse <dwmw@amazon.co.uk>

Set 'e' correctly to reflect the location that Xen is actually relocated
to from its default 2MiB location. Not 2MiB below that.

This is only vaguely a bug fix. The "missing" 2MiB would have been used
in the end, and fed to the allocator. It's just that other things don't
get to sit right up *next* to the Xen image, and it isn't very tidy.

For live update, I'd quite like a single contiguous region for the
reserved bootmem and Xen, allowing the 'slack' in the former to be used
when Xen itself grows larger. Let's not allow 2MiB of random heap pages
to get in the way...

Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
---
 xen/arch/x86/setup.c | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/xen/arch/x86/setup.c b/xen/arch/x86/setup.c
index d858883404..2677f127b9 100644
--- a/xen/arch/x86/setup.c
+++ b/xen/arch/x86/setup.c
@@ -1080,9 +1080,9 @@ void __init noreturn __start_xen(unsigned long mbi_p)
             unsigned long pte_update_limit;
 
             /* Select relocation address. */
-            e = end - reloc_size;
-            xen_phys_start = e;
-            bootsym(trampoline_xen_phys_start) = e;
+            xen_phys_start = end - reloc_size;
+            e = xen_phys_start + XEN_IMG_OFFSET;
+            bootsym(trampoline_xen_phys_start) = xen_phys_start;
 
             /*
              * No PTEs pointing above this address are candidates for relocation.
@@ -1090,7 +1090,7 @@ void __init noreturn __start_xen(unsigned long mbi_p)
              * and the beginning of region for destination image some PTEs may
              * point to addresses in range [e, e + XEN_IMG_OFFSET).
              */
-            pte_update_limit = PFN_DOWN(e + XEN_IMG_OFFSET);
+            pte_update_limit = PFN_DOWN(e);
 
             /*
              * Perform relocation to new physical address.
@@ -1099,7 +1099,7 @@ void __init noreturn __start_xen(unsigned long mbi_p)
              * data until after we have switched to the relocated pagetables!
              */
             barrier();
-            move_memory(e + XEN_IMG_OFFSET, XEN_IMG_OFFSET, _end - _start, 1);
+            move_memory(e, XEN_IMG_OFFSET, _end - _start, 1);
 
             /* Walk initial pagetables, relocating page directory entries. */
             pl4e = __va(__pa(idle_pg_table));
-- 
2.21.0


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