[Xen-devel] [PATCH 2/3] xen: correct race in alloc_p2m_pmd()

[Juergen Gross <jgross@xxxxxxxx>]

When allocating a new pmd for the linear mapped p2m list a check is
done for not introducing another pmd when this just happened on
another cpu. In this case the old pte pointer was returned which
points to the p2m_missing or p2m_identity page. The correct value
would be the pointer to the found new page.

Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
---
 arch/x86/xen/p2m.c | 9 +++------
 1 file changed, 3 insertions(+), 6 deletions(-)

diff --git a/arch/x86/xen/p2m.c b/arch/x86/xen/p2m.c
index 36ae094..fdb996e 100644
--- a/arch/x86/xen/p2m.c
+++ b/arch/x86/xen/p2m.c
@@ -440,10 +440,9 @@ EXPORT_SYMBOL_GPL(get_phys_to_machine);
  * a new pmd is to replace p2m_missing_pte or p2m_identity_pte by a individual
  * pmd. In case of PAE/x86-32 there are multiple pmds to allocate!
  */
-static pte_t *alloc_p2m_pmd(unsigned long addr, pte_t *ptep, pte_t *pte_pg)
+static pte_t *alloc_p2m_pmd(unsigned long addr, pte_t *pte_pg)
 {
        pte_t *ptechk;
-       pte_t *pteret = ptep;
        pte_t *pte_newpg[PMDS_PER_MID_PAGE];
        pmd_t *pmdp;
        unsigned int level;
@@ -477,8 +476,6 @@ static pte_t *alloc_p2m_pmd(unsigned long addr, pte_t 
*ptep, pte_t *pte_pg)
                if (ptechk == pte_pg) {
                        set_pmd(pmdp,
                                __pmd(__pa(pte_newpg[i]) | _KERNPG_TABLE));
-                       if (vaddr == (addr & ~(PMD_SIZE - 1)))
-                               pteret = pte_offset_kernel(pmdp, addr);
                        pte_newpg[i] = NULL;
                }
 
@@ -492,7 +489,7 @@ static pte_t *alloc_p2m_pmd(unsigned long addr, pte_t 
*ptep, pte_t *pte_pg)
                vaddr += PMD_SIZE;
        }
 
-       return pteret;
+       return lookup_address(addr, &level);
 }
 
 /*
@@ -521,7 +518,7 @@ static bool alloc_p2m(unsigned long pfn)
 
        if (pte_pg == p2m_missing_pte || pte_pg == p2m_identity_pte) {
                /* PMD level is missing, allocate a new one */
-               ptep = alloc_p2m_pmd(addr, ptep, pte_pg);
+               ptep = alloc_p2m_pmd(addr, pte_pg);
                if (!ptep)
                        return false;
        }
-- 
2.1.2


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