From: Michael Kelley <redacted> Sent: Thursday, February 4, 2021 3:36 PM

From: Sunil Muthuswamy <redacted> Sent: Wednesday, January 6, 2021
3:21 PM

quoted

Linux has support for free page reporting now (36e66c554b5c) for
virtualized environment. On Hyper-V when virtually backed VMs are
configured, Hyper-V will advertise cold memory discard capability,
when supported. This patch adds the support to hook into the free
page reporting infrastructure and leverage the Hyper-V cold memory
discard hint hypercall to report/free these pages back to the host.

Signed-off-by: Sunil Muthuswamy <redacted>
Tested-by: Matheus Castello <matheus@castello.eng.br>
---
In V2:
- Addressed feedback comments
- Added page reporting config option tied to hyper-v balloon config

In V3:
- Addressed feedback from Vitaly
---
 arch/x86/hyperv/hv_init.c         | 31 +++++++++++
 arch/x86/kernel/cpu/mshyperv.c    |  6 +-
 drivers/hv/Kconfig                |  1 +
 drivers/hv/hv_balloon.c           | 93 +++++++++++++++++++++++++++++++
 include/asm-generic/hyperv-tlfs.h | 32 ++++++++++-
 include/asm-generic/mshyperv.h    |  2 +
 6 files changed, 162 insertions(+), 3 deletions(-)

[snip]

quoted

+
+	BUILD_BUG_ON(PAGE_REPORTING_CAPACITY > HV_MEMORY_HINT_MAX_GPA_PAGE_RANGES);
+	dm_device.pr_dev_info.report = hv_free_page_report;
+	ret = page_reporting_register(&dm_device.pr_dev_info);
+	if (ret < 0) {
+		dm_device.pr_dev_info.report = NULL;
+		pr_err("Failed to enable cold memory discard: %d\n", ret);
+	} else {
+		pr_info("Cold memory discard hint enabled\n");
+	}

Should the above two messages be prefixed with "Hyper-V: "?

Ignore the above comment.  The lines will get prefixed with
"hv_balloon:", which is fine.

Michael