[Xen-devel] [PATCH v3 1/3] xen/arm: implement steal_page

[Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>]

Signed-off-by: Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>
---
 xen/arch/arm/mm.c |   43 +++++++++++++++++++++++++++++++++++++++++++
 1 files changed, 43 insertions(+), 0 deletions(-)

diff --git a/xen/arch/arm/mm.c b/xen/arch/arm/mm.c
index f301e65..ea64c03 100644
--- a/xen/arch/arm/mm.c
+++ b/xen/arch/arm/mm.c
@@ -751,6 +751,49 @@ int donate_page(struct domain *d, struct page_info *page, 
unsigned int memflags)
 int steal_page(
     struct domain *d, struct page_info *page, unsigned int memflags)
 {
+    unsigned long x, y;
+    bool_t drop_dom_ref = 0;
+
+    spin_lock(&d->page_alloc_lock);
+
+    if ( is_xen_heap_page(page) || (page_get_owner(page) != d) )
+        goto fail;
+
+    /*
+     * We require there is just one reference (PGC_allocated). We temporarily
+     * drop this reference now so that we can safely swizzle the owner.
+     */
+    y = page->count_info;
+    do {
+        x = y;
+        if ( (x & (PGC_count_mask|PGC_allocated)) != (1 | PGC_allocated) )
+            goto fail;
+        y = cmpxchg(&page->count_info, x, x & ~PGC_count_mask);
+    } while ( y != x );
+
+    /* Swizzle the owner then reinstate the PGC_allocated reference. */
+    page_set_owner(page, NULL);
+    y = page->count_info;
+    do {
+        x = y;
+        BUG_ON((x & (PGC_count_mask|PGC_allocated)) != PGC_allocated);
+    } while ( (y = cmpxchg(&page->count_info, x, x | 1)) != x );
+
+    /* Unlink from original owner. */
+    if ( !(memflags & MEMF_no_refcount) && !domain_adjust_tot_pages(d, -1) )
+        drop_dom_ref = 1;
+    page_list_del(page, &d->page_list);
+
+    spin_unlock(&d->page_alloc_lock);
+    if ( unlikely(drop_dom_ref) )
+        put_domain(d);
+    return 0;
+
+ fail:
+    spin_unlock(&d->page_alloc_lock);
+    printk("Bad page %p: ed=%p(%u), sd=%p, caf=%08lx, taf=%lx\n",
+            (void *)page_to_mfn(page), d, d->domain_id,
+            page_get_owner(page), page->count_info, page->u.inuse.type_info);
     return -1;
 }
 
-- 
1.7.2.5


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