RE: [PATCH v3] x86/Hyper-V: Support for free page reporting

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(-)

diff --git a/arch/x86/hyperv/hv_init.c b/arch/x86/hyperv/hv_init.c
index e04d90af4c27..5b610e47d091 100644
--- a/arch/x86/hyperv/hv_init.c
+++ b/arch/x86/hyperv/hv_init.c

@@ -528,3 +528,34 @@ bool hv_is_hibernation_supported(void)
 	return acpi_sleep_state_supported(ACPI_STATE_S4);
 }
 EXPORT_SYMBOL_GPL(hv_is_hibernation_supported);
+
+/* Bit mask of the extended capability to query: see HV_EXT_CAPABILITY_xxx */
+bool hv_query_ext_cap(u64 cap_query)
+{
+	u64 *cap;
+	unsigned long flags;
+	u64 ext_cap = 0;
+
+	/*
+	 * Querying extended capabilities is an extended hypercall. Check if the
+	 * partition supports extended hypercall, first.
+	 */
+	if (!(ms_hyperv.priv_high & HV_ENABLE_EXTENDED_HYPERCALLS))
+		return 0;

+EXPORT_SYMBOL_GPL(hv_query_ext_cap);

diff --git a/arch/x86/kernel/cpu/mshyperv.c b/arch/x86/kernel/cpu/mshyperv.c
index 05ef1f4550cb..f4c0d69c61ae 100644
--- a/arch/x86/kernel/cpu/mshyperv.c
+++ b/arch/x86/kernel/cpu/mshyperv.c

@@ -225,11 +225,13 @@ static void __init ms_hyperv_init_platform(void)
 	 * Extract the features and hints
 	 */
 	ms_hyperv.features = cpuid_eax(HYPERV_CPUID_FEATURES);
+	ms_hyperv.priv_high = cpuid_ebx(HYPERV_CPUID_FEATURES);
 	ms_hyperv.misc_features = cpuid_edx(HYPERV_CPUID_FEATURES);
 	ms_hyperv.hints    = cpuid_eax(HYPERV_CPUID_ENLIGHTMENT_INFO);

-	pr_info("Hyper-V: features 0x%x, hints 0x%x, misc 0x%x\n",
-		ms_hyperv.features, ms_hyperv.hints, ms_hyperv.misc_features);
+	pr_info("Hyper-V: privilege flags low:0x%x, high:0x%x, hints:0x%x, misc:0x%x\n",

+		ms_hyperv.features, ms_hyperv.priv_high, ms_hyperv.hints,
+		ms_hyperv.misc_features);

 	ms_hyperv.max_vp_index = cpuid_eax(HYPERV_CPUID_IMPLEMENT_LIMITS);
 	ms_hyperv.max_lp_index = cpuid_ebx(HYPERV_CPUID_IMPLEMENT_LIMITS);

diff --git a/drivers/hv/Kconfig b/drivers/hv/Kconfig
index 79e5356a737a..66c794d92391 100644
--- a/drivers/hv/Kconfig
+++ b/drivers/hv/Kconfig

@@ -23,6 +23,7 @@ config HYPERV_UTILS
 config HYPERV_BALLOON
 	tristate "Microsoft Hyper-V Balloon driver"
 	depends on HYPERV
+	select PAGE_REPORTING

 	help
 	  Select this option to enable Hyper-V Balloon driver.

diff --git a/drivers/hv/hv_balloon.c b/drivers/hv/hv_balloon.c
index 8c471823a5af..c0ff0a48f540 100644
--- a/drivers/hv/hv_balloon.c
+++ b/drivers/hv/hv_balloon.c

@@ -21,6 +21,7 @@
 #include <linux/memory.h>
 #include <linux/notifier.h>
 #include <linux/percpu_counter.h>
+#include <linux/page_reporting.h>

 #include <linux/hyperv.h>
 #include <asm/hyperv-tlfs.h>

@@ -563,6 +564,10 @@ struct hv_dynmem_device {
 	 * The negotiated version agreed by host.
 	 */
 	__u32 version;
+
+#ifdef CONFIG_PAGE_REPORTING
+	struct page_reporting_dev_info pr_dev_info;
+#endif
 };

 static struct hv_dynmem_device dm_device;

@@ -1568,6 +1573,84 @@ static void balloon_onchannelcallback(void *context)

 }

+#ifdef CONFIG_PAGE_REPORTING
+/* Hyper-V only supports reporting 2MB pages or higher */

+}
+
+static void disable_page_reporting(void)
+{
+	if (dm_device.pr_dev_info.report) {
+		page_reporting_unregister(&dm_device.pr_dev_info);
+		dm_device.pr_dev_info.report = NULL;
+	}
+}
+#endif /* CONFIG_PAGE_REPORTING */
+
 static int balloon_connect_vsp(struct hv_device *dev)
 {
 	struct dm_version_request version_req;

@@ -1713,6 +1796,10 @@ static int balloon_probe(struct hv_device *dev,
 	if (ret != 0)
 		return ret;

+#ifdef CONFIG_PAGE_REPORTING
+	enable_page_reporting();
+#endif
+
 	dm_device.state = DM_INITIALIZED;

 	dm_device.thread =

@@ -1731,6 +1818,9 @@ static int balloon_probe(struct hv_device *dev,
 #ifdef CONFIG_MEMORY_HOTPLUG
 	unregister_memory_notifier(&hv_memory_nb);
 	restore_online_page_callback(&hv_online_page);
+#endif
+#ifdef CONFIG_PAGE_REPORTING
+	disable_page_reporting();
 #endif

 	return ret;
 }

@@ -1753,6 +1843,9 @@ static int balloon_remove(struct hv_device *dev)
 #ifdef CONFIG_MEMORY_HOTPLUG
 	unregister_memory_notifier(&hv_memory_nb);
 	restore_online_page_callback(&hv_online_page);
+#endif
+#ifdef CONFIG_PAGE_REPORTING
+	disable_page_reporting();
 #endif

 	spin_lock_irqsave(&dm_device.ha_lock, flags);
 	list_for_each_entry_safe(has, tmp, &dm->ha_region_list, list) {

diff --git a/include/asm-generic/hyperv-tlfs.h b/include/asm-generic/hyperv-tlfs.h
index e73a11850055..75c20be2cc44 100644
--- a/include/asm-generic/hyperv-tlfs.h
+++ b/include/asm-generic/hyperv-tlfs.h

@@ -89,6 +89,7 @@
 #define HV_ACCESS_STATS				BIT(8)
 #define HV_DEBUGGING				BIT(11)
 #define HV_CPU_POWER_MANAGEMENT			BIT(12)
+#define HV_ENABLE_EXTENDED_HYPERCALLS		BIT(20)


 /*

@@ -152,11 +153,18 @@ struct ms_hyperv_tsc_page {
 #define HVCALL_FLUSH_GUEST_PHYSICAL_ADDRESS_SPACE 0x00af
 #define HVCALL_FLUSH_GUEST_PHYSICAL_ADDRESS_LIST 0x00b0

+/* Extended hypercalls */
+#define HV_EXT_CALL_QUERY_CAPABILITIES		0x8001
+#define HV_EXT_CALL_MEMORY_HEAT_HINT		0x8003
+
 #define HV_FLUSH_ALL_PROCESSORS			BIT(0)
 #define HV_FLUSH_ALL_VIRTUAL_ADDRESS_SPACES	BIT(1)
 #define HV_FLUSH_NON_GLOBAL_MAPPINGS_ONLY	BIT(2)
 #define HV_FLUSH_USE_EXTENDED_RANGE_FORMAT	BIT(3)

+/* Extended capability bits */
+#define HV_EXT_CAPABILITY_MEMORY_COLD_DISCARD_HINT BIT(8)
+
 enum HV_GENERIC_SET_FORMAT {
 	HV_GENERIC_SET_SPARSE_4K,
 	HV_GENERIC_SET_ALL,

@@ -367,7 +375,7 @@ struct hv_guest_mapping_flush {
  */
 #define HV_MAX_FLUSH_PAGES (2048)

-/* HvFlushGuestPhysicalAddressList hypercall */
+/* HvFlushGuestPhysicalAddressList, HvExtCallMemoryHeatHint hypercall */
 union hv_gpa_page_range {
 	u64 address_space;
 	struct {

@@ -375,6 +383,12 @@ union hv_gpa_page_range {
 		u64 largepage:1;
 		u64 basepfn:52;
 	} page;
+	struct {
+		u64 reserved:12;
+		u64 page_size:1;
+		u64 reserved1:8;
+		u64 base_large_pfn:43;
+	};
 };

 /*

@@ -494,4 +508,20 @@ struct hv_set_vp_registers_input {
 	} element[];
 } __packed;

+/*
+ * The whole argument should fit in a page to be able to pass to the hypervisor
+ * in one hypercall.
+ */
+#define HV_MEMORY_HINT_MAX_GPA_PAGE_RANGES  \
+	((PAGE_SIZE - sizeof(struct hv_memory_hint)) / \

+		sizeof(union hv_gpa_page_range))
+
+/* HvExtCallMemoryHeatHint hypercall */
+#define HV_EXT_MEMORY_HEAT_HINT_TYPE_COLD_DISCARD	2
+struct hv_memory_hint {
+	u64 type:2;
+	u64 reserved:62;
+	union hv_gpa_page_range ranges[];
+} __packed;
+
 #endif

diff --git a/include/asm-generic/mshyperv.h b/include/asm-generic/mshyperv.h
index c57799684170..93c1303f5e00 100644
--- a/include/asm-generic/mshyperv.h
+++ b/include/asm-generic/mshyperv.h

@@ -27,6 +27,7 @@

 struct ms_hyperv_info {
 	u32 features;
+	u32 priv_high;
 	u32 misc_features;
 	u32 hints;
 	u32 nested_features;

@@ -170,6 +171,7 @@ void hyperv_report_panic_msg(phys_addr_t pa, size_t size);
 bool hv_is_hyperv_initialized(void);
 bool hv_is_hibernation_supported(void);
 void hyperv_cleanup(void);
+bool hv_query_ext_cap(u64 cap_query);
 #else /* CONFIG_HYPERV */
 static inline bool hv_is_hyperv_initialized(void) { return false; }
 static inline bool hv_is_hibernation_supported(void) { return false; }
--

2.17.1