[Xen-devel] [PATCH] xen: correctly rebuild mfn list list after migration.

[Ian Campbell <ian.campbell@xxxxxxxxxx>]

Otherwise the second migration attempt fails because the mfn_list_list
still refers to all the old mfns.

We need to update the entires in both p2m_top_mfn and the mid_mfn
pages which p2m_top_mfn refers to.

In order to do this we need to keep track of the virtual addresses
mapping the p2m_mid_mfn pages since we cannot rely on
mfn_to_virt(p2m_top_mfn[idx]) since p2m_top_mfn[idx] will still
contain the old MFN after a migration, which may now belong to another
domain and hence have a different mapping in the m2p.

Therefore add and maintain a third top level page, p2m_mid_mfn_p[],
which tracks the virtual addresses of the mfns contained in
p2m_top_mfn[].

We also need to update the content of the p2m_mid_missing_mfn page on
resume to refer to the page's new mfn.

p2m_missing does not need updating since the migration process takes
care of the leaf p2m pages for us.

Signed-off-by: Ian Campbell <ian.campbell@xxxxxxxxxx>
---
 arch/x86/xen/mmu.c |   49 ++++++++++++++++++++++++++++++++++++++-----------
 1 files changed, 38 insertions(+), 11 deletions(-)

diff --git a/arch/x86/xen/mmu.c b/arch/x86/xen/mmu.c
index 16a8e25..8788064 100644
--- a/arch/x86/xen/mmu.c
+++ b/arch/x86/xen/mmu.c
@@ -185,6 +185,8 @@ DEFINE_PER_CPU(unsigned long, xen_current_cr3);      /* 
actual vcpu cr3 */
  *    / \      / \         /           /
  *  p2m p2m p2m p2m p2m p2m p2m ...
  *
+ * The p2m_mid_mfn pages are mapped by p2m_mid_mfn_p.
+ *
  * The p2m_top and p2m_top_mfn levels are limited to 1 page, so the
  * maximum representable pseudo-physical address space is:
  *  P2M_TOP_PER_PAGE * P2M_MID_PER_PAGE * P2M_PER_PAGE pages
@@ -209,6 +211,7 @@ static RESERVE_BRK_ARRAY(unsigned long, 
p2m_mid_missing_mfn, P2M_MID_PER_PAGE);
 
 static RESERVE_BRK_ARRAY(unsigned long **, p2m_top, P2M_TOP_PER_PAGE);
 static RESERVE_BRK_ARRAY(unsigned long, p2m_top_mfn, P2M_TOP_PER_PAGE);
+static RESERVE_BRK_ARRAY(unsigned long *, p2m_mid_mfn_p, P2M_TOP_PER_PAGE);
 
 RESERVE_BRK(p2m_mid, PAGE_SIZE * (MAX_DOMAIN_PAGES / (P2M_PER_PAGE * 
P2M_MID_PER_PAGE)));
 RESERVE_BRK(p2m_mid_mfn, PAGE_SIZE * (MAX_DOMAIN_PAGES / (P2M_PER_PAGE * 
P2M_MID_PER_PAGE)));
@@ -245,6 +248,14 @@ static void p2m_top_mfn_init(unsigned long *top)
                top[i] = virt_to_mfn(p2m_mid_missing_mfn);
 }
 
+static void p2m_mid_mfn_p_init(unsigned long **top)
+{
+       unsigned i;
+
+       for (i = 0; i < P2M_TOP_PER_PAGE; i++)
+               top[i] = p2m_mid_missing_mfn;
+}
+
 static void p2m_mid_init(unsigned long **mid)
 {
        unsigned i;
@@ -301,15 +312,21 @@ EXPORT_SYMBOL(create_lookup_pte_addr);
  */
 void xen_build_mfn_list_list(void)
 {
-       unsigned pfn;
+       unsigned long pfn;
 
        /* Pre-initialize p2m_top_mfn to be completely missing */
        if (p2m_top_mfn == NULL) {
                p2m_mid_missing_mfn = extend_brk(PAGE_SIZE, PAGE_SIZE);
                p2m_mid_mfn_init(p2m_mid_missing_mfn);
 
+               p2m_mid_mfn_p = extend_brk(PAGE_SIZE, PAGE_SIZE);
+               p2m_mid_mfn_p_init(p2m_mid_mfn_p);
+
                p2m_top_mfn = extend_brk(PAGE_SIZE, PAGE_SIZE);
                p2m_top_mfn_init(p2m_top_mfn);
+       } else {
+               /* Reinitialise, mfn's all change after migration */
+               p2m_mid_mfn_init(p2m_mid_missing_mfn);
        }
 
        for (pfn = 0; pfn < xen_max_p2m_pfn; pfn += P2M_PER_PAGE) {
@@ -322,14 +339,19 @@ void xen_build_mfn_list_list(void)
                mid = p2m_top[topidx];
 
                /* Don't bother allocating any mfn mid levels if
-                  they're just missing */
-               if (mid[mididx] == p2m_missing)
+                * they're just missing, just update the stored mfn,
+                * since all could have changed over a migrate.
+                */
+               if (mid == p2m_mid_missing) {
+                       p2m_top_mfn[topidx] = virt_to_mfn(p2m_mid_missing);
+                       pfn += P2M_MID_PER_PAGE - 1;
                        continue;
+               }
 
-               mid_mfn = p2m_top_mfn[topidx];
-               mid_mfn_p = mfn_to_virt(mid_mfn);
+               mid_mfn_p = p2m_mid_mfn_p[topidx];
+               mid_mfn = virt_to_mfn(mid_mfn_p);
 
-               if (mid_mfn_p == p2m_mid_missing_mfn) {
+               if (mid_mfn_p == p2m_missing) {
                        /*
                         * XXX boot-time only!  We should never find
                         * missing parts of the mfn tree after
@@ -340,10 +362,11 @@ void xen_build_mfn_list_list(void)
                        p2m_mid_mfn_init(mid_mfn_p);
 
                        mid_mfn = virt_to_mfn(mid_mfn_p);
-                       
-                       p2m_top_mfn[topidx] = mid_mfn;
+                       p2m_mid_mfn_p[topidx] = mid_mfn_p;
                }
 
+               p2m_top_mfn[topidx] = mid_mfn;
+
                mid_mfn_p[mididx] = virt_to_mfn(mid[mididx]);
        }
 }
@@ -362,7 +385,7 @@ void __init xen_build_dynamic_phys_to_machine(void)
 {
        unsigned long *mfn_list = (unsigned long *)xen_start_info->mfn_list;
        unsigned long max_pfn = min(MAX_DOMAIN_PAGES, xen_start_info->nr_pages);
-       unsigned pfn;
+       unsigned long pfn;
 
        xen_max_p2m_pfn = max_pfn;
 
@@ -452,7 +475,9 @@ static bool alloc_p2m(unsigned long pfn)
        }
 
        top_mfn_p = &p2m_top_mfn[topidx];
-       mid_mfn = mfn_to_virt(*top_mfn_p);
+       mid_mfn = p2m_mid_mfn_p[topidx];
+
+       BUG_ON(mid_mfn != mfn_to_virt(*top_mfn_p));
 
        if (mid_mfn == p2m_mid_missing_mfn) {
                /* Separately check the mid mfn level */
@@ -464,11 +489,13 @@ static bool alloc_p2m(unsigned long pfn)
                        return false;
 
                p2m_mid_mfn_init(mid_mfn);
-               
+
                missing_mfn = virt_to_mfn(p2m_mid_missing_mfn);
                mid_mfn_mfn = virt_to_mfn(mid_mfn);
                if (cmpxchg(top_mfn_p, missing_mfn, mid_mfn_mfn) != missing_mfn)
                        free_p2m_page(mid_mfn);
+               else
+                       p2m_mid_mfn_p[topidx] = mid_mfn;
        }
 
        if (p2m_top[topidx][mididx] == p2m_missing) {
-- 
1.5.6.5


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