Re: [PATCH 2/2] xen: before ballooning hotplugged memory, set frames to invalid

From: Juergen Gross
Date: Thu Mar 19 2015 - 13:22:15 EST

On 03/19/2015 05:21 PM, Daniel Kiper wrote:
On Thu, Mar 19, 2015 at 03:31:02PM +0100, Juergen Gross wrote:
Commit 25b884a83d487fd62c3de7ac1ab5549979188482 ("x86/xen: set
regions above the end of RAM as 1:1") introduced a regression.

To be able to add memory pages which were added via memory hotplug to
a pv domain, the pages must be "invalid" instead of "identity" in the
p2m list before they can be added.

Suggested-by: David Vrabel <david.vrabel@xxxxxxxxxx>
Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
drivers/xen/balloon.c | 13 +++++++++++--
1 file changed, 11 insertions(+), 2 deletions(-)

diff --git a/drivers/xen/balloon.c b/drivers/xen/balloon.c
index 0b52d92..52e331f 100644
--- a/drivers/xen/balloon.c
+++ b/drivers/xen/balloon.c
@@ -221,15 +221,24 @@ static bool balloon_is_inflated(void)

static enum bp_state reserve_additional_memory(long credit)
- int nid, rc;
+ int nid, rc = 0;
u64 hotplug_start_paddr;
unsigned long balloon_hotplug = credit;
+ unsigned long pfn;

hotplug_start_paddr = PFN_PHYS(SECTION_ALIGN_UP(max_pfn));
balloon_hotplug = round_up(balloon_hotplug, PAGES_PER_SECTION);
nid = memory_add_physaddr_to_nid(hotplug_start_paddr);

- rc = add_memory(nid, hotplug_start_paddr, balloon_hotplug << PAGE_SHIFT);
+ for (pfn = PFN_DOWN(hotplug_start_paddr);
+ !rc && pfn < PFN_DOWN(hotplug_start_paddr) + balloon_hotplug;
+ pfn++)
+ if (!set_phys_to_machine(pfn, INVALID_P2M_ENTRY))

rc = set_phys_to_machine(pfn, INVALID_P2M_ENTRY)?

Not really. set_phys_to_machine returns false on failure...

+ rc = 1;

I do not think that this stuff is needed for HVM or PVH guests.


+ if (!rc)
+ rc = add_memory(nid, hotplug_start_paddr,
+ balloon_hotplug << PAGE_SHIFT);

if (rc) {
pr_warn("Cannot add additional memory (%i)\n", rc);

It will be nice to know what part of infrastructure failed.
Could you create separate pr_warn() message for set_phys_to_machine()?

Value 1 for rc is the indicator for that case.

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