@@ -44,6 +44,7 @@ config KVM
select KVM_VFIO
select SRCU
select HAVE_KVM_PM_NOTIFIER if PM
+ select MEMFD_OPS
help
Support hosting fully virtualized guest machines using hardware
virtualization extensions. You will need a fairly recent
@@ -11,7 +11,8 @@ KVM := ../../../virt/kvm
kvm-y += $(KVM)/kvm_main.o $(KVM)/coalesced_mmio.o \
$(KVM)/eventfd.o $(KVM)/irqchip.o $(KVM)/vfio.o \
- $(KVM)/dirty_ring.o $(KVM)/binary_stats.o
+ $(KVM)/dirty_ring.o $(KVM)/binary_stats.o \
+ $(KVM)/memfd.o
kvm-$(CONFIG_KVM_ASYNC_PF) += $(KVM)/async_pf.o
kvm-y += x86.o emulate.o i8259.o irq.o lapic.o \
@@ -773,6 +773,14 @@ static inline void kvm_irqfd_exit(void)
{
}
#endif
+
+int kvm_memfd_register(struct kvm *kvm,
+ const struct kvm_userspace_memory_region_ext *mem,
+ struct kvm_memory_slot *slot);
+void kvm_memfd_unregister(struct kvm *kvm, struct kvm_memory_slot *slot);
+long kvm_memfd_get_pfn(struct kvm_memory_slot *slot, gfn_t gfn, int *order);
+void kvm_memfd_put_pfn(kvm_pfn_t pfn);
+
int kvm_init(void *opaque, unsigned vcpu_size, unsigned vcpu_align,
struct module *module);
void kvm_exit(void);
new file mode 100644
@@ -0,0 +1,95 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * memfd.c: routines for fd based guest memory
+ * Copyright (c) 2021, Intel Corporation.
+ *
+ * Author:
+ * Chao Peng <chao.p.peng@linux.intel.com>
+ */
+
+#include <linux/kvm_host.h>
+#include <linux/memfd.h>
+
+#ifdef CONFIG_MEMFD_OPS
+static const struct memfd_pfn_ops *memfd_ops;
+
+static void memfd_invalidate_page_range(struct inode *inode, void *owner,
+ pgoff_t start, pgoff_t end)
+{
+}
+
+static void memfd_fallocate(struct inode *inode, void *owner,
+ pgoff_t start, pgoff_t end)
+{
+}
+
+static bool memfd_get_owner(void *owner)
+{
+ return kvm_get_kvm_safe(owner);
+}
+
+static void memfd_put_owner(void *owner)
+{
+ kvm_put_kvm(owner);
+}
+
+static const struct memfd_falloc_notifier memfd_notifier = {
+ .invalidate_page_range = memfd_invalidate_page_range,
+ .fallocate = memfd_fallocate,
+ .get_owner = memfd_get_owner,
+ .put_owner = memfd_put_owner,
+};
+#endif
+
+long kvm_memfd_get_pfn(struct kvm_memory_slot *slot, gfn_t gfn, int *order)
+{
+#ifdef CONFIG_MEMFD_OPS
+ pgoff_t index = gfn - slot->base_gfn +
+ (slot->file_ofs >> PAGE_SHIFT);
+
+ return memfd_ops->get_lock_pfn(slot->file->f_inode, index, order);
+#else
+ return -1;
+#endif
+}
+
+void kvm_memfd_put_pfn(kvm_pfn_t pfn)
+{
+#ifdef CONFIG_MEMFD_OPS
+ memfd_ops->put_unlock_pfn(pfn);
+#endif
+}
+
+int kvm_memfd_register(struct kvm *kvm,
+ const struct kvm_userspace_memory_region_ext *mem,
+ struct kvm_memory_slot *slot)
+{
+#ifdef CONFIG_MEMFD_OPS
+ int ret;
+ struct fd fd = fdget(mem->fd);
+
+ if (!fd.file)
+ return -EINVAL;
+
+ ret = memfd_register_falloc_notifier(fd.file->f_inode, kvm,
+ &memfd_notifier, &memfd_ops);
+ if (ret)
+ return ret;
+
+ slot->file = fd.file;
+ slot->file_ofs = mem->ofs;
+ return 0;
+#else
+ return -EOPNOTSUPP;
+#endif
+}
+
+void kvm_memfd_unregister(struct kvm *kvm, struct kvm_memory_slot *slot)
+{
+#ifdef CONFIG_MEMFD_OPS
+ if (slot->file) {
+ fput(slot->file);
+ slot->file = NULL;
+ }
+#endif
+}
This patch adds the new memfd facility in KVM using MEMFD_OPS to provide guest memory from a file descriptor created in user space with memfd_create() instead of traditional userspace hva. It mainly provides two kind of functions: - Pair/unpair a fd-based memslot to a memory backend that owns the file descriptor when such memslot gets created/deleted. - Get/put a pfn that to be used in KVM page fault handler from/to the paired memory backend. At the pairing time, KVM and the memfd subsystem exchange calllbacks that each can call into the other side. These callbacks are the major places to implement fd-based guest memory provisioning. KVM->memfd: - get_pfn: get and lock a page at specified offset in the fd. - put_pfn: put and unlock the pfn. Note: page needs to be locked between get_pfn/put_pfn to ensure pfn is valid when KVM uses it to establish the mapping in the secondary MMU page table. memfd->KVM: - invalidate_page_range: called when userspace punch hole on the fd, KVM should unmap related pages in the second MMU. - fallocate: called when userspace fallocate space on the fd, KVM can map related pages in the second MMU. - get/put_owner: used to ensure guest is still alive using a reference mechanism when calling above invalidate/fallocate callbacks. Signed-off-by: Yu Zhang <yu.c.zhang@linux.intel.com> Signed-off-by: Chao Peng <chao.p.peng@linux.intel.com> --- arch/x86/kvm/Kconfig | 1 + arch/x86/kvm/Makefile | 3 +- include/linux/kvm_host.h | 8 ++++ virt/kvm/memfd.c | 95 ++++++++++++++++++++++++++++++++++++++++ 4 files changed, 106 insertions(+), 1 deletion(-) create mode 100644 virt/kvm/memfd.c