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Re: [Xen-devel] HVM support for e820_host (Was: Bug: Limitation of <=2GB RAM in domU persists with 4.3.0)

On 09/03/2013 10:30 PM, Konrad Rzeszutek Wilk wrote:
On Tue, Sep 03, 2013 at 10:24:44PM +0100, Gordan Bobic wrote:
On 09/03/2013 10:10 PM, Konrad Rzeszutek Wilk wrote:
On Tue, Sep 03, 2013 at 09:49:40PM +0100, Gordan Bobic wrote:
I spoke too soon - even with e820_host=0, the same error occurs.
What did I break? The code in question is this:

if (libxl_defbool_val(d_config->b_info.e820_host)) {
     ret = libxl__e820_alloc(gc, domid, d_config);
     if (ret) {
         LIBXL__LOG_ERRNO(gc->owner, LIBXL__LOG_ERROR,
                 "Failed while collecting E820 with: %d (errno:%d)\n",
                 ret, errno);

With e820_host=0, that outer black should evaluate to false, should
it not? In libxl_create.c, if I am understanding the code correctly,
e820_host is defaulted to false, too. What am I missing?

Does your config have 'pci' in it? The patch you sent had this:

+        if (d_config->num_pcidevs)
+            libxl_defbool_set(&b_info->e820_host, true);

Which means that even if you did not have e820_host it will be automatically
set if you have PCI devices.

OK - that was embarrasing. Caffeine underflow error. :(
I backed out that block. I don't think e820_host should be implicit in hvm when PCI devices are passed.

That makes the adjusted patch fragment:
--- xl_cmdimpl.c.orig   2013-09-04 00:42:57.424337503 +0100
+++ xl_cmdimpl.c        2013-09-04 00:43:21.213886356 +0100
@@ -1293,7 +1293,7 @@
         if (d_config->num_pcidevs && c_info->type == LIBXL_DOMAIN_TYPE_PV)
-            libxl_defbool_set(&b_info->u.pv.e820_host, true);
+            libxl_defbool_set(&b_info->e820_host, true);

     switch (xlu_cfg_get_list(config, "cpuid", &cpuids, 0, 1)) {

This should maintain the old behaviour for backward compatibility when e820_host is not set. I just tested it and it works (with e820_host=1 I get the previous error, with e820_host=0, everything works fine.

I will have a play with the other two patches tomorrow.


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