libxl: setup shadow memory according to max hotplug memory

The '<maxMemory>' domain XML element is about maximum memory to be hot
plugged. Make libxl support this for calculating shadow memory amount,
which is used by Xen for internal accounting of domain memory (among
other things). If shadow memory is calculated based on initial memory,
then the domain can hotplug up to about twice that memory, but not more
(it silently doesn't get more).

QubesOS/qubes-issues#7956

0022-libxl-setup-shadow-memory-according-to-max-hotplug-m.patch

@@ -0,0 +1,55 @@
+From 3a9226aa90cd9d3e7da4bb2e1de7bc72dab087a9 Mon Sep 17 00:00:00 2001
+From: =?UTF-8?q?Marek=20Marczykowski-G=C3=B3recki?=
+ <[email protected]>
+Date: Sat, 5 Aug 2023 22:53:39 +0200
+Subject: [PATCH] libxl: setup shadow memory according to max hotplug memory
+MIME-Version: 1.0
+Content-Type: text/plain; charset=UTF-8
+Content-Transfer-Encoding: 8bit
+
+The '<maxMemory>' domain XML element is about maximum memory to be hot
+plugged. Make libxl support this for calculating shadow memory amount,
+which is used by Xen for internal accounting of domain memory (among
+other things). If shadow memory is calculated based on initial memory,
+then the domain can hotplug up to about twice that memory, but not more
+(it silently doesn't get more).
+
+The 'slots' attribute of the '<maxMemory>' element is ignored.
+
+Signed-off-by: Marek Marczykowski-Górecki <[email protected]>
+---
+ src/libxl/libxl_conf.c   | 5 +++--
+ src/libxl/libxl_domain.c | 1 +
+ 2 files changed, 4 insertions(+), 2 deletions(-)
+
+diff --git a/src/libxl/libxl_conf.c b/src/libxl/libxl_conf.c
+index fd57ebf79b..f89f2dd978 100644
+--- a/src/libxl/libxl_conf.c
++++ b/src/libxl/libxl_conf.c
+@@ -874,8 +874,9 @@ libxlMakeDomBuildInfo(virDomainDef *def,
+
+     /* Allow libxl to calculate shadow memory requirements */
+     b_info->shadow_memkb =
+-        libxl_get_required_shadow_memory(b_info->max_memkb,
+-                                         b_info->max_vcpus);
++        libxl_get_required_shadow_memory(
++                def->mem.max_memory ? : b_info->max_memkb,
++                b_info->max_vcpus);
+
+     if (def->namespaceData) {
+         libxlDomainXmlNsDef *nsdata = def->namespaceData;
+diff --git a/src/libxl/libxl_domain.c b/src/libxl/libxl_domain.c
+index 8620efc4f0..6c2313fdf8 100644
+--- a/src/libxl/libxl_domain.c
++++ b/src/libxl/libxl_domain.c
+@@ -325,6 +325,7 @@ virDomainDefParserConfig libxlDomainDefParserConfig = {
+
+     .features = VIR_DOMAIN_DEF_FEATURE_USER_ALIAS |
+                 VIR_DOMAIN_DEF_FEATURE_FW_AUTOSELECT |
++                VIR_DOMAIN_DEF_FEATURE_MEMORY_HOTPLUG |
+                 VIR_DOMAIN_DEF_FEATURE_NET_MODEL_STRING,
+ };
+
+-- 
+2.41.0
+

libvirt.spec.in

@@ -299,6 +299,7 @@ Patch0018: 0018-Revert-meson-Replace-meson.build_root-with-meson.pro.patch
 Patch0019: 0019-Revert-meson-Bump-minimal-required-meson-version.patch
 Patch0020: 0020-libxl-adjust-ich6-sound-card-name.patch
 Patch0021: 0021-libxl-set-net-disk-trusted-parameter-based-on-backen.patch
+Patch0022: 0022-libxl-setup-shadow-memory-according-to-max-hotplug-m.patch
 
 Requires: libvirt-daemon = %{epoch}:%{version}-%{release}
 %if %{with_network}