[Xen-devel] [PATCH] xen/e820: Don't mark balloon memory as E820_UNUSABLE when running as guest.

[Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>]

If we have a guest that asked for:

memory=1024
maxmem=20448

Which means we want 1GB now, and create pagetables so that we can expand
up to 2GB, we would have this E820 layout:

[    0.000000] BIOS-provided physical RAM map:
[    0.000000]  Xen: 0000000000000000 - 00000000000a0000 (usable)
[    0.000000]  Xen: 00000000000a0000 - 0000000000100000 (reserved)
[    0.000000]  Xen: 0000000000100000 - 0000000080800000 (usable)

Due to patch: "xen/setup: Inhibit resource API from using System RAM E820 gaps 
as PCI mem gaps."
we would mark the memory past the 1GB mark as unusuable resulting in:

[    0.000000] BIOS-provided physical RAM map:
[    0.000000]  Xen: 0000000000000000 - 00000000000a0000 (usable)
[    0.000000]  Xen: 00000000000a0000 - 0000000000100000 (reserved)
[    0.000000]  Xen: 0000000000100000 - 0000000040000000 (usable)
[    0.000000]  Xen: 0000000040000000 - 0000000080800000 (unusable)

which meant that we could not balloon up anymore. We could
balloon the guest down. The fix is to run the code introduced
by the above mentioned patch only for the initial domain.

We will have to revisit this once we start introducing a modified
E820 for PCI passthrough so that we can utilize the P2M identity code.

Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
---
 arch/x86/xen/setup.c |    3 ++-
 1 files changed, 2 insertions(+), 1 deletions(-)

diff --git a/arch/x86/xen/setup.c b/arch/x86/xen/setup.c
index 2a4add9..6e676fa 100644
--- a/arch/x86/xen/setup.c
+++ b/arch/x86/xen/setup.c
@@ -200,7 +200,8 @@ char * __init xen_memory_setup(void)
                         * used as potential resource for I/O address (happens
                         * when 'allocate_resource' is called).
                         */
-                       if (delta && end < 0x100000000UL)
+                       if (delta &&
+                               (xen_initial_domain() && end < 0x100000000UL))
                                e820_add_region(end, delta, E820_UNUSABLE);
                }
 
-- 
1.7.1


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