Re: [PATCH 1/2] xen: prepare p2m list for memory hotplug

From: Juergen Gross
Date: Thu Mar 19 2015 - 13:21:50 EST


On 03/19/2015 05:14 PM, Daniel Kiper wrote:
On Thu, Mar 19, 2015 at 03:31:01PM +0100, Juergen Gross wrote:
Commit 054954eb051f35e74b75a566a96fe756015352c8 ("xen: switch to linear
virtual mapped sparse p2m list") introduced a regression regarding to
memory hotplug for a pv-domain: as the virtual space for the p2m list
is allocated for the to be expected memory size of the domain only,
hotplugged memory above that size will not be usable by the domain.

Correct this by using a configurable size for the p2m list in case of
memory hotplug enabled (default supported memory size is 512 GB for
64 bit domains and 4 GB for 32 bit domains).

Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
---
arch/x86/xen/p2m.c | 13 ++++++++++++-
drivers/xen/Kconfig | 13 +++++++++++++
2 files changed, 25 insertions(+), 1 deletion(-)

diff --git a/arch/x86/xen/p2m.c b/arch/x86/xen/p2m.c
index 9f93af5..30e84ae 100644
--- a/arch/x86/xen/p2m.c
+++ b/arch/x86/xen/p2m.c
@@ -91,6 +91,17 @@ EXPORT_SYMBOL_GPL(xen_p2m_size);
unsigned long xen_max_p2m_pfn __read_mostly;
EXPORT_SYMBOL_GPL(xen_max_p2m_pfn);

+#ifdef CONFIG_XEN_BALLOON_MEMORY_HOTPLUG_LIMIT
+#ifdef CONFIG_X86_32
+BUILD_BUG_ON_MSG(CONFIG_XEN_BALLOON_MEMORY_HOTPLUG_LIMIT > 64)
+#endif
+#define P2M_LIMIT max(xen_max_p2m_pfn, \
+ ((unsigned long)((u64)CONFIG_XEN_BALLOON_MEMORY_HOTPLUG_LIMIT * \
+ 1024 * 1024 * 1024 / PAGE_SIZE)))
+#else
+#define P2M_LIMIT xen_max_p2m_pfn
+#endif
+
static DEFINE_SPINLOCK(p2m_update_lock);

static unsigned long *p2m_mid_missing_mfn;
@@ -387,7 +398,7 @@ void __init xen_vmalloc_p2m_tree(void)
static struct vm_struct vm;

vm.flags = VM_ALLOC;
- vm.size = ALIGN(sizeof(unsigned long) * xen_max_p2m_pfn,
+ vm.size = ALIGN(sizeof(unsigned long) * P2M_LIMIT,
PMD_SIZE * PMDS_PER_MID_PAGE);

What happens when somebody will allocate more memory for guest than
XEN_BALLOON_MEMORY_HOTPLUG_LIMIT? Additionally, I think that we do

It will fail to add like it does without this patch.

not need allocate extra virtual address space if memory hotplug is
disabled.

As XEN_BALLOON_MEMORY_HOTPLUG_LIMIT depends on
XEN_BALLOON_MEMORY_HOTPLUG which in turn depends on MEMORY_HOTPLUG,
this is already the case.


vm_area_register_early(&vm, PMD_SIZE * PMDS_PER_MID_PAGE);
pr_notice("p2m virtual area at %p, size is %lx\n", vm.addr, vm.size);
diff --git a/drivers/xen/Kconfig b/drivers/xen/Kconfig
index b812462..0a61ddf 100644
--- a/drivers/xen/Kconfig
+++ b/drivers/xen/Kconfig
@@ -55,6 +55,19 @@ config XEN_BALLOON_MEMORY_HOTPLUG

In that case step 3 should be omitted.

+config XEN_BALLOON_MEMORY_HOTPLUG_LIMIT
+ int
+ default 512 if X86_64
+ default 4 if X86_32
+ depends on XEN_HAVE_PVMMU

Do we need dependency on XEN_HAVE_PVMMU?

Yes. Needed only for pv domains.

If yes than maybe "depends on XEN_HAVE_PVMMU && XEN_BALLOON_MEMORY_HOTPLUG".

Matter of taste, I guess.


+ depends on XEN_BALLOON_MEMORY_HOTPLUG

Should not this option be available even when memory hotplug is disabled?

Why?


Juergen
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