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 <[e-mail]>
Tested-by: Matheus Castello <[e-mail]>
Reviewed-by: Michael Kelley <[e-mail]>
Tested-by: Nathan Chancellor <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Wei Liu <[e-mail]>

arch/x86/hyperv/hv_init.c

···
 		x86_init.irqs.create_pci_msi_domain = hv_create_pci_msi_domain;
 #endif
 
+	/* Query the VMs extended capability once, so that it can be cached. */
+	hv_query_ext_cap(0);
 	return;
 
 remove_cpuhp_state:
···
 
 enum hv_isolation_type hv_get_isolation_type(void)
 {
-	if (!(ms_hyperv.features_b & HV_ISOLATION))
+	if (!(ms_hyperv.priv_high & HV_ISOLATION))
 		return HV_ISOLATION_TYPE_NONE;
 	return FIELD_GET(HV_ISOLATION_TYPE, ms_hyperv.isolation_config_b);
 }
···
 	return hv_get_isolation_type() != HV_ISOLATION_TYPE_NONE;
 }
 EXPORT_SYMBOL_GPL(hv_is_isolation_supported);
+
+/* Bit mask of the extended capability to query: see HV_EXT_CAPABILITY_xxx */
+bool hv_query_ext_cap(u64 cap_query)
+{
+	/*
+	 * The address of the 'hv_extended_cap' variable will be used as an
+	 * output parameter to the hypercall below and so it should be
+	 * compatible with 'virt_to_phys'. Which means, it's address should be
+	 * directly mapped. Use 'static' to keep it compatible; stack variables
+	 * can be virtually mapped, making them imcompatible with
+	 * 'virt_to_phys'.
+	 * Hypercall input/output addresses should also be 8-byte aligned.
+	 */
+	static u64 hv_extended_cap __aligned(8);
+	static bool hv_extended_cap_queried;
+	u64 status;
+
+	/*
+	 * 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 false;
+
+	/* Extended capabilities do not change at runtime. */
+	if (hv_extended_cap_queried)
+		return hv_extended_cap & cap_query;
+
+	status = hv_do_hypercall(HV_EXT_CALL_QUERY_CAPABILITIES, NULL,
+				 &hv_extended_cap);
+
+	/*
+	 * The query extended capabilities hypercall should not fail under
+	 * any normal circumstances. Avoid repeatedly making the hypercall, on
+	 * error.
+	 */
+	hv_extended_cap_queried = true;
+	status &= HV_HYPERCALL_RESULT_MASK;
+	if (status != HV_STATUS_SUCCESS) {
+		pr_err("Hyper-V: Extended query capabilities hypercall failed 0x%llx\n",
+		       status);
+		return false;
+	}
+
+	return hv_extended_cap & cap_query;
+}
+EXPORT_SYMBOL_GPL(hv_query_ext_cap);

arch/x86/kernel/cpu/mshyperv.c

···
 	 * Extract the features and hints
 	 */
 	ms_hyperv.features = cpuid_eax(HYPERV_CPUID_FEATURES);
-	ms_hyperv.features_b = cpuid_ebx(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);
···
 		x86_platform.calibrate_cpu = hv_get_tsc_khz;
 	}
 
-	if (ms_hyperv.features_b & HV_ISOLATION) {
+	if (ms_hyperv.priv_high & HV_ISOLATION) {
 		ms_hyperv.isolation_config_a = cpuid_eax(HYPERV_CPUID_ISOLATION_CONFIG);
 		ms_hyperv.isolation_config_b = cpuid_ebx(HYPERV_CPUID_ISOLATION_CONFIG);
 

drivers/hv/Kconfig

···
 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.
 

drivers/hv/hv_balloon.c

···
 #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>
···
 	 * The negotiated version agreed by host.
 	 */
 	__u32 version;
+
+	struct page_reporting_dev_info pr_dev_info;
 };
 
 static struct hv_dynmem_device dm_device;
···
 
 }
 
+/* Hyper-V only supports reporting 2MB pages or higher */
+#define HV_MIN_PAGE_REPORTING_ORDER	9
+#define HV_MIN_PAGE_REPORTING_LEN (HV_HYP_PAGE_SIZE << HV_MIN_PAGE_REPORTING_ORDER)
+static int hv_free_page_report(struct page_reporting_dev_info *pr_dev_info,
+		    struct scatterlist *sgl, unsigned int nents)
+{
+	unsigned long flags;
+	struct hv_memory_hint *hint;
+	int i;
+	u64 status;
+	struct scatterlist *sg;
+
+	WARN_ON_ONCE(nents > HV_MEMORY_HINT_MAX_GPA_PAGE_RANGES);
+	WARN_ON_ONCE(sgl->length < HV_MIN_PAGE_REPORTING_LEN);
+	local_irq_save(flags);
+	hint = *(struct hv_memory_hint **)this_cpu_ptr(hyperv_pcpu_input_arg);
+	if (!hint) {
+		local_irq_restore(flags);
+		return -ENOSPC;
+	}
+
+	hint->type = HV_EXT_MEMORY_HEAT_HINT_TYPE_COLD_DISCARD;
+	hint->reserved = 0;
+	for_each_sg(sgl, sg, nents, i) {
+		union hv_gpa_page_range *range;
+
+		range = &hint->ranges[i];
+		range->address_space = 0;
+		/* page reporting only reports 2MB pages or higher */
+		range->page.largepage = 1;
+		range->page.additional_pages =
+			(sg->length / HV_MIN_PAGE_REPORTING_LEN) - 1;
+		range->page_size = HV_GPA_PAGE_RANGE_PAGE_SIZE_2MB;
+		range->base_large_pfn =
+			page_to_hvpfn(sg_page(sg)) >> HV_MIN_PAGE_REPORTING_ORDER;
+	}
+
+	status = hv_do_rep_hypercall(HV_EXT_CALL_MEMORY_HEAT_HINT, nents, 0,
+				     hint, NULL);
+	local_irq_restore(flags);
+	if ((status & HV_HYPERCALL_RESULT_MASK) != HV_STATUS_SUCCESS) {
+		pr_err("Cold memory discard hypercall failed with status %llx\n",
+			status);
+		return -EINVAL;
+	}
+
+	return 0;
+}
+
+static void enable_page_reporting(void)
+{
+	int ret;
+
+	/* Essentially, validating 'PAGE_REPORTING_MIN_ORDER' is big enough. */
+	if (pageblock_order < HV_MIN_PAGE_REPORTING_ORDER) {
+		pr_debug("Cold memory discard is only supported on 2MB pages and above\n");
+		return;
+	}
+
+	if (!hv_query_ext_cap(HV_EXT_CAPABILITY_MEMORY_COLD_DISCARD_HINT)) {
+		pr_debug("Cold memory discard hint not supported by Hyper-V\n");
+		return;
+	}
+
+	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");
+	}
+}
+
+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;
+	}
+}
+
 static int balloon_connect_vsp(struct hv_device *dev)
 {
 	struct dm_version_request version_req;
···
 	if (ret != 0)
 		return ret;
 
+	enable_page_reporting();
 	dm_device.state = DM_INITIALIZED;
 
 	dm_device.thread =
···
 probe_error:
 	dm_device.state = DM_INIT_ERROR;
 	dm_device.thread  = NULL;
+	disable_page_reporting();
 	vmbus_close(dev->channel);
 #ifdef CONFIG_MEMORY_HOTPLUG
 	unregister_memory_notifier(&hv_memory_nb);
···
 	cancel_work_sync(&dm->ha_wrk.wrk);
 
 	kthread_stop(dm->thread);
+	disable_page_reporting();
 	vmbus_close(dev->channel);
 #ifdef CONFIG_MEMORY_HOTPLUG
 	unregister_memory_notifier(&hv_memory_nb);

include/asm-generic/hyperv-tlfs.h

···
 #define HV_ACCESS_STATS				BIT(8)
 #define HV_DEBUGGING				BIT(11)
 #define HV_CPU_MANAGEMENT			BIT(12)
+#define HV_ENABLE_EXTENDED_HYPERCALLS		BIT(20)
 #define HV_ISOLATION				BIT(22)
-
 
 /*
  * TSC page layout.
···
 #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,
···
  *  by the bitwidth of "additional_pages" in union hv_gpa_page_range.
  */
 #define HV_MAX_FLUSH_PAGES (2048)
+#define HV_GPA_PAGE_RANGE_PAGE_SIZE_2MB		0
+#define HV_GPA_PAGE_RANGE_PAGE_SIZE_1GB		1
 
-/* HvFlushGuestPhysicalAddressList hypercall */
+/* HvFlushGuestPhysicalAddressList, HvExtCallMemoryHeatHint hypercall */
 union hv_gpa_page_range {
 	u64 address_space;
 	struct {
···
 		u64 largepage:1;
 		u64 basepfn:52;
 	} page;
+	struct {
+		u64 reserved:12;
+		u64 page_size:1;
+		u64 reserved1:8;
+		u64 base_large_pfn:43;
+	};
 };
 
 /*
···
 
 #define HV_SOURCE_SHADOW_NONE               0x0
 #define HV_SOURCE_SHADOW_BRIDGE_BUS_RANGE   0x1
+
+/*
+ * 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  \
+	((HV_HYP_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

include/asm-generic/mshyperv.h

···
 
 struct ms_hyperv_info {
 	u32 features;
-	u32 features_b;
+	u32 priv_high;
 	u32 misc_features;
 	u32 hints;
 	u32 nested_features;
···
 enum hv_isolation_type hv_get_isolation_type(void);
 bool hv_is_isolation_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; }