[RFC][Patch v8 1/7] KVM: Support for guest free page hinting

[Nitesh Narayan Lal]

This patch includes the following:
1. Basic skeleton for the support
2. Enablement of x86 platform to use the same

Signed-off-by: Nitesh Narayan Lal <nitesh@xxxxxxxxxx>
---
 arch/x86/Kbuild              |  2 +-
 arch/x86/kvm/Kconfig         |  8 ++++++++
 arch/x86/kvm/Makefile        |  2 ++
 include/linux/gfp.h          |  9 +++++++++
 include/linux/page_hinting.h | 17 +++++++++++++++++
 virt/kvm/page_hinting.c      | 36 ++++++++++++++++++++++++++++++++++++
 6 files changed, 73 insertions(+), 1 deletion(-)
 create mode 100644 include/linux/page_hinting.h
 create mode 100644 virt/kvm/page_hinting.c

diff --git a/arch/x86/Kbuild b/arch/x86/Kbuild
index c625f57472f7..3244df4ee311 100644
--- a/arch/x86/Kbuild
+++ b/arch/x86/Kbuild
@@ -2,7 +2,7 @@ obj-y += entry/
 
 obj-$(CONFIG_PERF_EVENTS) += events/
 
-obj-$(CONFIG_KVM) += kvm/
+obj-$(subst m,y,$(CONFIG_KVM)) += kvm/
 
 # Xen paravirtualization support
 obj-$(CONFIG_XEN) += xen/
diff --git a/arch/x86/kvm/Kconfig b/arch/x86/kvm/Kconfig
index 72fa955f4a15..2fae31459706 100644
--- a/arch/x86/kvm/Kconfig
+++ b/arch/x86/kvm/Kconfig
@@ -96,6 +96,14 @@ config KVM_MMU_AUDIT
 	 This option adds a R/W kVM module parameter 'mmu_audit', which allows
 	 auditing of KVM MMU events at runtime.
 
+# KVM_FREE_PAGE_HINTING will allow the guest to report the free pages to the
+# host in regular interval of time.
+config KVM_FREE_PAGE_HINTING
+       def_bool y
+       depends on KVM
+       select VIRTIO
+       select VIRTIO_BALLOON
+
 # OK, it's a little counter-intuitive to do this, but it puts it neatly under
 # the virtualization menu.
 source "drivers/vhost/Kconfig"
diff --git a/arch/x86/kvm/Makefile b/arch/x86/kvm/Makefile
index 69b3a7c30013..78640a80501e 100644
--- a/arch/x86/kvm/Makefile
+++ b/arch/x86/kvm/Makefile
@@ -16,6 +16,8 @@ kvm-y			+= x86.o mmu.o emulate.o i8259.o irq.o lapic.o \
 			   i8254.o ioapic.o irq_comm.o cpuid.o pmu.o mtrr.o \
 			   hyperv.o page_track.o debugfs.o
 
+obj-$(CONFIG_KVM_FREE_PAGE_HINTING)    += $(KVM)/page_hinting.o
+
 kvm-intel-y		+= vmx/vmx.o vmx/vmenter.o vmx/pmu_intel.o vmx/vmcs12.o vmx/evmcs.o vmx/nested.o
 kvm-amd-y		+= svm.o pmu_amd.o
 
diff --git a/include/linux/gfp.h b/include/linux/gfp.h
index 5f5e25fd6149..e596527284ba 100644
--- a/include/linux/gfp.h
+++ b/include/linux/gfp.h
@@ -7,6 +7,7 @@
 #include <linux/stddef.h>
 #include <linux/linkage.h>
 #include <linux/topology.h>
+#include <linux/page_hinting.h>
 
 struct vm_area_struct;
 
@@ -456,6 +457,14 @@ static inline struct zonelist *node_zonelist(int nid, gfp_t flags)
 	return NODE_DATA(nid)->node_zonelists + gfp_zonelist(flags);
 }
 
+#ifdef	CONFIG_KVM_FREE_PAGE_HINTING
+#define HAVE_ARCH_FREE_PAGE
+static inline void arch_free_page(struct page *page, int order)
+{
+	guest_free_page(page, order);
+}
+#endif
+
 #ifndef HAVE_ARCH_FREE_PAGE
 static inline void arch_free_page(struct page *page, int order) { }
 #endif
diff --git a/include/linux/page_hinting.h b/include/linux/page_hinting.h
new file mode 100644
index 000000000000..b54f7428f348
--- /dev/null
+++ b/include/linux/page_hinting.h
@@ -0,0 +1,17 @@
+/*
+ * Size of the array which is used to store the freed pages is defined by
+ * MAX_FGPT_ENTRIES. If possible, we have to find a better way using which
+ * we can get rid of the hardcoded array size.
+ */
+#define MAX_FGPT_ENTRIES	1000
+/*
+ * hypervisor_pages - It is a dummy structure passed with the hypercall.
+ * @pfn: page frame number for the page which needs to be sent to the host.
+ * @order: order of the page needs to be reported to the host.
+ */
+struct hypervisor_pages {
+	unsigned long pfn;
+	unsigned int order;
+};
+
+void guest_free_page(struct page *page, int order);
diff --git a/virt/kvm/page_hinting.c b/virt/kvm/page_hinting.c
new file mode 100644
index 000000000000..818bd6b84e0c
--- /dev/null
+++ b/virt/kvm/page_hinting.c
@@ -0,0 +1,36 @@
+#include <linux/gfp.h>
+#include <linux/mm.h>
+#include <linux/kernel.h>
+
+/*
+ * struct kvm_free_pages - Tracks the pages which are freed by the guest.
+ * @pfn: page frame number for the page which is freed.
+ * @order: order corresponding to the page freed.
+ * @zonenum: zone number to which the freed page belongs.
+ */
+struct kvm_free_pages {
+	unsigned long pfn;
+	unsigned int order;
+	int zonenum;
+};
+
+/*
+ * struct page_hinting - holds array objects for the structures used to track
+ * guest free pages, along with an index variable for each of them.
+ * @kvm_pt: array object for the structure kvm_free_pages.
+ * @kvm_pt_idx: index for kvm_free_pages object.
+ * @hypervisor_pagelist: array object for the structure hypervisor_pages.
+ * @hyp_idx: index for hypervisor_pages object.
+ */
+struct page_hinting {
+	struct kvm_free_pages kvm_pt[MAX_FGPT_ENTRIES];
+	int kvm_pt_idx;
+	struct hypervisor_pages hypervisor_pagelist[MAX_FGPT_ENTRIES];
+	int hyp_idx;
+};
+
+DEFINE_PER_CPU(struct page_hinting, hinting_obj);
+
+void guest_free_page(struct page *page, int order)
+{
+}
-- 
2.17.2