xl, e820_host, PV passthrough: Fix guests crashing when memory == maxmem

The code had an obvious bug where it would assume that the balloon
amount would always be _something_ and add an E820_RAM entry at the
end of the E820 array. The added E820_RAM would contain the balloon amount
plus the delta of memory that had to be subtracted b/c of the various
E820 entries. That assumption is certainly true when maxmem != mem,
but if guest config has maxmem = memory that is incorrect (as balloon
value is zero). The end result is that the E820 that is constructed
is missing a swath of "delta" memory and in most cases ends up with
only one E820_RAM entry that is of 512MB size on many Intel systems.

Reported-by: Christian Holpert <christian@holpert.de>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Acked-by: Ian Campbell <ian.campbell@citrix.com>

diff --git a/tools/libxl/libxl_x86.c b/tools/libxl/libxl_x86.c
index a17f6ae63b6e610c0f517c35acdaab256447f6f2..a78c91d8e3710c4b6396ff1d3840562f4127a239 100644 (file)
--- a/tools/libxl/libxl_x86.c
+++ b/tools/libxl/libxl_x86.c
@@ -182,7 +182,7 @@ static int e820_sanitize(libxl_ctx *ctx, struct e820entry src[],
         idx++;
     }
     /* At this point we have the mapped RAM + E820 entries from src. */
-    if (balloon_kb) {
+    if (balloon_kb || delta_kb) {
         /* and if we truncated the RAM region, then add it to the end. */
         e820[idx].type = E820_RAM;
         e820[idx].addr = (uint64_t)(1ULL << 32) > last ?