[Xen-devel] [PATCH 07/10] xen/mmu: Work with 1-1 mappings when allocating new top/middle entries.

[Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>]

We were not properly taking under advisement the 1-1 mappings
when a large area of memory was ballooned out.

Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
---
 arch/x86/xen/mmu.c |   13 ++++++++-----
 1 files changed, 8 insertions(+), 5 deletions(-)

diff --git a/arch/x86/xen/mmu.c b/arch/x86/xen/mmu.c
index bd02e7d..92f4fec 100644
--- a/arch/x86/xen/mmu.c
+++ b/arch/x86/xen/mmu.c
@@ -464,7 +464,7 @@ static void free_p2m_page(void *p)
 static bool alloc_p2m(unsigned long pfn)
 {
        unsigned topidx, mididx;
-       unsigned long ***top_p, **mid;
+       unsigned long ***top_p, **mid, **mid_orig;
        unsigned long *top_mfn_p, *mid_mfn;
 
        topidx = p2m_top_index(pfn);
@@ -473,15 +473,16 @@ static bool alloc_p2m(unsigned long pfn)
        top_p = &p2m_top[topidx];
        mid = *top_p;
 
-       if (mid == p2m_mid_identity) {
+       if (mid == p2m_mid_identity || mid == p2m_mid_missing) {
                /* Mid level is missing, allocate a new one */
+               mid_orig = mid;
                mid = alloc_p2m_page();
                if (!mid)
                        return false;
 
                p2m_mid_init(mid, p2m_identity);
 
-               if (cmpxchg(top_p, p2m_mid_identity, mid) != p2m_mid_identity)
+               if (cmpxchg(top_p, mid_orig, mid) != mid_orig)
                        free_p2m_page(mid);
        }
 
@@ -510,9 +511,11 @@ static bool alloc_p2m(unsigned long pfn)
                        p2m_top_mfn_p[topidx] = mid_mfn;
        }
 
-       if (p2m_top[topidx][mididx] == p2m_identity) {
+       if (p2m_top[topidx][mididx] == p2m_identity ||
+           p2m_top[topidx][mididx] == p2m_missing) {
                /* p2m leaf page is missing */
                unsigned long *p2m;
+               unsigned long *p2m_orig = p2m_top[topidx][mididx];
 
                p2m = alloc_p2m_page();
                if (!p2m)
@@ -520,7 +523,7 @@ static bool alloc_p2m(unsigned long pfn)
 
                p2m_init(p2m);
 
-               if (cmpxchg(&mid[mididx], p2m_identity, p2m) != p2m_identity)
+               if (cmpxchg(&mid[mididx], p2m_orig, p2m) != p2m_orig)
                        free_p2m_page(p2m);
                else
                        mid_mfn[mididx] = virt_to_mfn(p2m);
-- 
1.7.1


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