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Re: [Xen-devel] [PATCH v5 1/1] Add mmio_hole_size

On 09/30/2014 09:22 AM, George Dunlap wrote:
On Tue, Sep 30, 2014 at 2:27 AM, Boris Ostrovsky
<boris.ostrovsky@xxxxxxxxxx> wrote:
+    if ( mmio_hole_size )
+    {
+        uint64_t max_ram_below_4g = (1ULL << 32) - mmio_hole_size;
+        if ( max_ram_below_4g > HVM_BELOW_4G_MMIO_START )
+        {
+            printf("max_ram_below_4g=0x"PRIllx
+                   " too big for mmio_hole_size=0x"PRIllx
+                   " has been ignored.\n",
+                   PRIllx_arg(max_ram_below_4g),
+                   PRIllx_arg(mmio_hole_size));
+        }

Do you need to check whether the hole is too large?

Here and in the toolstack.
How large is too large?  I've seen real machines with a 3GiB memory hole...

But if mmio_hole_size is set to, say, 4GB we can't expect anything good, right? I don't know what the reasonable upper limit on it should be but it seems to me we need one. Especially given that it's a uint64_t.


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