[Xen-devel] [PATCH 3/3] x86/e820: fix 640k - 1M region reservation logic

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

From: Sergey Dyasli <sergey.dyasli@xxxxxxxxxx>

Converting a guest from PV to PV-in-PVH makes the guest to have 384k
less memory, which may confuse guest's balloon driver. This happens
because Xen unconditionally reserves 640k - 1M region in E820 despite
the fact that it's really a usable RAM in PVH boot mode.

Fix this by skipping region type change in virtualised environments,
trusting whatever memory map our hypervisor has provided.

Signed-off-by: Sergey Dyasli <sergey.dyasli@xxxxxxxxxx>
---
CC: Jan Beulich <JBeulich@xxxxxxxx>
CC: Wei Liu <wl@xxxxxxx>
CC: Roger Pau Monné <roger.pau@xxxxxxxxxx>
CC: Sergey Dyasli <sergey.dyasli@xxxxxxxxxx>
CC: Juergen Gross <jgross@xxxxxxxx>
---
 xen/arch/x86/e820.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/xen/arch/x86/e820.c b/xen/arch/x86/e820.c
index 8e8a2c4e1b..082f9928a1 100644
--- a/xen/arch/x86/e820.c
+++ b/xen/arch/x86/e820.c
@@ -318,9 +318,9 @@ static int __init copy_e820_map(struct e820entry * biosmap, 
unsigned int nr_map)
 
         /*
          * Some BIOSes claim RAM in the 640k - 1M region.
-         * Not right. Fix it up.
+         * Not right. Fix it up, but only when running on bare metal.
          */
-        if (type == E820_RAM) {
+        if (!cpu_has_hypervisor && type == E820_RAM) {
             if (start < 0x100000ULL && end > 0xA0000ULL) {
                 if (start < 0xA0000ULL)
                     add_memory_region(start, 0xA0000ULL-start, type);
-- 
2.11.0


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