[Xen-devel] [PATCH v2 for 4.13 2/2] x86/e820: fix 640k - 1M region reservation logic

[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: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
CC: Wei Liu <wl@xxxxxxx>
CC: "Roger Pau Monné" <roger.pau@xxxxxxxxxx>
CC: Juergen Gross <jgross@xxxxxxxx>
---
 xen/arch/x86/e820.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/xen/arch/x86/e820.c b/xen/arch/x86/e820.c
index 8e8a2c4e1b..30ab8d9b35 100644
--- a/xen/arch/x86/e820.c
+++ b/xen/arch/x86/e820.c
@@ -318,9 +318,10 @@ 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);
-- 
2.17.1


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