[Xen-devel] [RFC PATCH v2 03/14] Don't add unused parts of live update reserved bootmem to heap

[David Woodhouse <dwmw2@xxxxxxxxxxxxx>]

From: David Woodhouse <dwmw@xxxxxxxxxxxx>

We need to promise that we won't use it for anything that will need to
persist across live update. Until we can achieve that (which will build
on of some of the work Hongyan is doing for secret hiding), the easy
answer is just not to add that region to the main heap at all. If
it was sized appropriately there isn't even much wastage.
---
 xen/arch/x86/setup.c    | 10 ++++++++++
 xen/common/page_alloc.c |  5 +++++
 xen/include/xen/mm.h    |  1 +
 3 files changed, 16 insertions(+)

diff --git a/xen/arch/x86/setup.c b/xen/arch/x86/setup.c
index 420c38456b..4296447d9f 100644
--- a/xen/arch/x86/setup.c
+++ b/xen/arch/x86/setup.c
@@ -1571,6 +1571,16 @@ void __init noreturn __start_xen(unsigned long mbi_p)
         unsigned long limit = virt_to_mfn(HYPERVISOR_VIRT_END - 1);
         uint64_t mask = PAGE_SIZE - 1;
 
+        /*
+         * Pages in the reserved LU region must not be used for anything which
+         * will need to persist across a live update. There is ongoing work to
+         * eliminate or limit the use of share_xen_page_with_guest() and get
+         * to a point where we can actually honour that promise, but for now
+         * just *don't* add those pages to the heap. Clear the boot allocator
+         * out completely, before adding the non-reserved ranges.
+         */
+        clear_boot_allocator();
+
         for ( i = 0; i < boot_e820.nr_map; i++ )
         {
             uint64_t s, e;
diff --git a/xen/common/page_alloc.c b/xen/common/page_alloc.c
index 919a270587..20ef25d45a 100644
--- a/xen/common/page_alloc.c
+++ b/xen/common/page_alloc.c
@@ -1879,6 +1879,11 @@ void __init end_boot_allocator(void)
     printk("\n");
 }
 
+void __init clear_boot_allocator(void)
+{
+    nr_bootmem_regions = 0;
+}
+
 static void __init smp_scrub_heap_pages(void *data)
 {
     unsigned long mfn, start, end;
diff --git a/xen/include/xen/mm.h b/xen/include/xen/mm.h
index 8d0ddfb60c..5bce174a3e 100644
--- a/xen/include/xen/mm.h
+++ b/xen/include/xen/mm.h
@@ -158,6 +158,7 @@ struct domain *__must_check 
page_get_owner_and_reference(struct page_info *);
 void init_boot_pages(paddr_t ps, paddr_t pe);
 mfn_t alloc_boot_pages(unsigned long nr_pfns, unsigned long pfn_align);
 void end_boot_allocator(void);
+void clear_boot_allocator(void);
 
 /* Xen suballocator. These functions are interrupt-safe. */
 void init_xenheap_pages(paddr_t ps, paddr_t pe);
-- 
2.21.0


_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxxxxxxxxx
https://lists.xenproject.org/mailman/listinfo/xen-devel