diff mbox series

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

Message ID 20191030145447.11122-2-sergey.dyasli@citrix.com (mailing list archive)
State New, archived
Headers show
Series [v2,for,4.13,1/2] x86/boot: allow early usage of cpu_has_hypervisor | expand

Commit Message

Sergey Dyasli Oct. 30, 2019, 2:54 p.m. UTC 
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@citrix.com>
---
CC: Jan Beulich <jbeulich@suse.com>
CC: Andrew Cooper <andrew.cooper3@citrix.com>
CC: Wei Liu <wl@xen.org>
CC: "Roger Pau Monné" <roger.pau@citrix.com>
CC: Juergen Gross <jgross@suse.com>
---
 xen/arch/x86/e820.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

Comments

Jan Beulich Oct. 30, 2019, 3:33 p.m. UTC | #1 
On 30.10.2019 15:54, Sergey Dyasli wrote:
> 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@citrix.com>

Reviewed-by: Jan Beulich <jbeulich@suse.com>
Wei Liu Oct. 31, 2019, 6:42 p.m. UTC | #2 
On Wed, Oct 30, 2019 at 02:54:47PM +0000, Sergey Dyasli wrote:
> 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@citrix.com>

Reviewed-by: Wei Liu <wl@xen.org>
diff mbox series

Patch

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);