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Re: [Xen-devel] [PATCH v3 1/3] x86/ldt: Make modify_ldt synchronous

On 07/22/2015 06:20 PM, Boris Ostrovsky wrote:
On 07/22/2015 03:23 PM, Andy Lutomirski wrote:

+    error = -ENOMEM;
+    new_ldt = alloc_ldt_struct(newsize);
+    if (!new_ldt)
          goto out_unlock;
-    }
  -    fill_ldt(&ldt, &ldt_info);
-    if (oldmode)
-        ldt.avl = 0;
+    if (old_ldt) {
+        memcpy(new_ldt->entries, old_ldt->entries,
+               oldsize * LDT_ENTRY_SIZE);
+    }
+    memset(new_ldt->entries + oldsize * LDT_ENTRY_SIZE, 0,
+           (newsize - oldsize) * LDT_ENTRY_SIZE);

We need to zero out full page (probably better in alloc_ldt_struct() with vmzalloc/__GFP_ZERO) --- Xen checks whole page that is assigned to G/LDT and gets unhappy if an invalid descriptor is found there.

This fixes one problem. There is something else that Xen gets upset about, I haven't figured what it is yet (and I am out tomorrow so it may need to wait until Friday).

What I thought was another problem turned out not to be one so both 64- and 32-bit tests passed on 64-bit PV (when allocated LDT is zeroed out)

However, on 32-bit kernel the test is failing multicpu test, I don't know yet what it is.


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