[PATCH RFC v15 20/30] virt: gunyah: Implement guestmemfd

[Elliot Berman]

Memory provided to Gunyah virtual machines are provided by a
Gunyah guestmemfd. Because memory provided to virtual machines may be
unmapped at stage-2 from the host (i.e. in the hypervisor's page tables
for the host), special care needs to be taken to ensure that the kernel
doesn't have a page mapped when it is lent to the guest. Without this
tracking, a kernel panic could be induced  by userspace tricking the
kernel into accessing guest-private memory.

Introduce the basic guestmemfd ops and ioctl. Userspace should be able
to access the memory unless it is provided to the guest virtual machine:
this is necessary to allow userspace to preload binaries such as the
kernel Image prior to running the VM. Subsequent commits will wire up
providing the memory to the guest.

Signed-off-by: Elliot Berman <quic_eberman@xxxxxxxxxxx>
---
 drivers/virt/gunyah/Makefile      |   2 +-
 drivers/virt/gunyah/guest_memfd.c | 269 ++++++++++++++++++++++++++++++++++++++
 drivers/virt/gunyah/vm_mgr.c      |   9 ++
 drivers/virt/gunyah/vm_mgr.h      |   2 +
 include/uapi/linux/gunyah.h       |  19 +++
 5 files changed, 300 insertions(+), 1 deletion(-)

diff --git a/drivers/virt/gunyah/Makefile b/drivers/virt/gunyah/Makefile
index ffcde0e0ccfa..9d514b2baa3a 100644
--- a/drivers/virt/gunyah/Makefile
+++ b/drivers/virt/gunyah/Makefile
@@ -1,6 +1,6 @@
 # SPDX-License-Identifier: GPL-2.0
 
-gunyah_rsc_mgr-y += rsc_mgr.o rsc_mgr_rpc.o vm_mgr.o vm_mgr_mem.o
+gunyah_rsc_mgr-y += rsc_mgr.o rsc_mgr_rpc.o vm_mgr.o vm_mgr_mem.o guest_memfd.o
 
 obj-$(CONFIG_GUNYAH) += gunyah.o gunyah_rsc_mgr.o gunyah_vcpu.o
 obj-$(CONFIG_GUNYAH_PLATFORM_HOOKS) += gunyah_platform_hooks.o
diff --git a/drivers/virt/gunyah/guest_memfd.c b/drivers/virt/gunyah/guest_memfd.c
new file mode 100644
index 000000000000..709aae9a1f44
--- /dev/null
+++ b/drivers/virt/gunyah/guest_memfd.c
@@ -0,0 +1,269 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright (c) 2023 Qualcomm Innovation Center, Inc. All rights reserved.
+ */
+
+#define pr_fmt(fmt) "gunyah_guest_mem: " fmt
+
+#include <linux/anon_inodes.h>
+#include <linux/types.h>
+#include <linux/falloc.h>
+#include <linux/file.h>
+#include <linux/migrate.h>
+#include <linux/pagemap.h>
+
+#include <uapi/linux/gunyah.h>
+
+static struct folio *gunyah_gmem_get_huge_folio(struct inode *inode,
+						pgoff_t index)
+{
+#ifdef CONFIG_TRANSPARENT_HUGEPAGE
+	unsigned long huge_index = round_down(index, HPAGE_PMD_NR);
+	unsigned long flags = (unsigned long)inode->i_private;
+	struct address_space *mapping = inode->i_mapping;
+	gfp_t gfp = mapping_gfp_mask(mapping);
+	struct folio *folio;
+
+	if (!(flags & GHMF_ALLOW_HUGEPAGE))
+		return NULL;
+
+	if (filemap_range_has_page(mapping, huge_index << PAGE_SHIFT,
+				   (huge_index + HPAGE_PMD_NR - 1)
+					   << PAGE_SHIFT))
+		return NULL;
+
+	folio = filemap_alloc_folio(gfp, HPAGE_PMD_ORDER);
+	if (!folio)
+		return NULL;
+
+	if (filemap_add_folio(mapping, folio, huge_index, gfp)) {
+		folio_put(folio);
+		return NULL;
+	}
+
+	return folio;
+#else
+	return NULL;
+#endif
+}
+
+static struct folio *gunyah_gmem_get_folio(struct inode *inode, pgoff_t index)
+{
+	struct folio *folio;
+
+	folio = gunyah_gmem_get_huge_folio(inode, index);
+	if (!folio) {
+		folio = filemap_grab_folio(inode->i_mapping, index);
+		if (IS_ERR_OR_NULL(folio))
+			return NULL;
+	}
+
+	/*
+	 * Use the up-to-date flag to track whether or not the memory has been
+	 * zeroed before being handed off to the guest.  There is no backing
+	 * storage for the memory, so the folio will remain up-to-date until
+	 * it's removed.
+	 */
+	if (!folio_test_uptodate(folio)) {
+		unsigned long nr_pages = folio_nr_pages(folio);
+		unsigned long i;
+
+		for (i = 0; i < nr_pages; i++)
+			clear_highpage(folio_page(folio, i));
+
+		folio_mark_uptodate(folio);
+	}
+
+	/*
+	 * Ignore accessed, referenced, and dirty flags.  The memory is
+	 * unevictable and there is no storage to write back to.
+	 */
+	return folio;
+}
+
+static vm_fault_t gunyah_gmem_host_fault(struct vm_fault *vmf)
+{
+	struct folio *folio;
+
+	folio = gunyah_gmem_get_folio(file_inode(vmf->vma->vm_file),
+				      vmf->pgoff);
+	if (!folio || folio_test_private(folio)) {
+		folio_unlock(folio);
+		folio_put(folio);
+		return VM_FAULT_SIGBUS;
+	}
+
+	vmf->page = folio_file_page(folio, vmf->pgoff);
+
+	return VM_FAULT_LOCKED;
+}
+
+static const struct vm_operations_struct gunyah_gmem_vm_ops = {
+	.fault = gunyah_gmem_host_fault,
+};
+
+static int gunyah_gmem_mmap(struct file *file, struct vm_area_struct *vma)
+{
+	file_accessed(file);
+	vma->vm_ops = &gunyah_gmem_vm_ops;
+	return 0;
+}
+
+static long gunyah_gmem_punch_hole(struct inode *inode, loff_t offset,
+				   loff_t len)
+{
+	truncate_inode_pages_range(inode->i_mapping, offset, offset + len - 1);
+
+	return 0;
+}
+
+static long gunyah_gmem_allocate(struct inode *inode, loff_t offset, loff_t len)
+{
+	struct address_space *mapping = inode->i_mapping;
+	pgoff_t start, index, end;
+	int r;
+
+	/* Dedicated guest is immutable by default. */
+	if (offset + len > i_size_read(inode))
+		return -EINVAL;
+
+	filemap_invalidate_lock_shared(mapping);
+
+	start = offset >> PAGE_SHIFT;
+	end = (offset + len) >> PAGE_SHIFT;
+
+	r = 0;
+	for (index = start; index < end;) {
+		struct folio *folio;
+
+		if (signal_pending(current)) {
+			r = -EINTR;
+			break;
+		}
+
+		folio = gunyah_gmem_get_folio(inode, index);
+		if (!folio) {
+			r = -ENOMEM;
+			break;
+		}
+
+		index = folio_next_index(folio);
+
+		folio_unlock(folio);
+		folio_put(folio);
+
+		/* 64-bit only, wrapping the index should be impossible. */
+		if (WARN_ON_ONCE(!index))
+			break;
+
+		cond_resched();
+	}
+
+	filemap_invalidate_unlock_shared(mapping);
+
+	return r;
+}
+
+static long gunyah_gmem_fallocate(struct file *file, int mode, loff_t offset,
+				  loff_t len)
+{
+	long ret;
+
+	if (!(mode & FALLOC_FL_KEEP_SIZE))
+		return -EOPNOTSUPP;
+
+	if (mode & ~(FALLOC_FL_KEEP_SIZE | FALLOC_FL_PUNCH_HOLE |
+		     FALLOC_FL_ZERO_RANGE))
+		return -EOPNOTSUPP;
+
+	if (!PAGE_ALIGNED(offset) || !PAGE_ALIGNED(len))
+		return -EINVAL;
+
+	if (mode & FALLOC_FL_PUNCH_HOLE)
+		ret = gunyah_gmem_punch_hole(file_inode(file), offset, len);
+	else
+		ret = gunyah_gmem_allocate(file_inode(file), offset, len);
+
+	if (!ret)
+		file_modified(file);
+	return ret;
+}
+
+static int gunyah_gmem_release(struct inode *inode, struct file *file)
+{
+	gunyah_gmem_punch_hole(inode, 0, U64_MAX);
+
+	return 0;
+}
+
+static const struct file_operations gunyah_gmem_fops = {
+	.owner = THIS_MODULE,
+	.llseek = generic_file_llseek,
+	.mmap = gunyah_gmem_mmap,
+	.open = generic_file_open,
+	.fallocate = gunyah_gmem_fallocate,
+	.release = gunyah_gmem_release,
+};
+
+static const struct address_space_operations gunyah_gmem_aops = {
+	.dirty_folio = noop_dirty_folio,
+	.migrate_folio = migrate_folio,
+	.error_remove_folio = generic_error_remove_folio,
+};
+
+int gunyah_guest_mem_create(struct gunyah_create_mem_args *args)
+{
+	const char *anon_name = "[gh-gmem]";
+	unsigned long fd_flags = 0;
+	struct inode *inode;
+	struct file *file;
+	int fd, err;
+
+	if (!PAGE_ALIGNED(args->size))
+		return -EINVAL;
+
+	if (args->flags & ~(GHMF_CLOEXEC | GHMF_ALLOW_HUGEPAGE))
+		return -EINVAL;
+
+	if (args->flags & GHMF_CLOEXEC)
+		fd_flags |= O_CLOEXEC;
+
+	fd = get_unused_fd_flags(fd_flags);
+	if (fd < 0)
+		return fd;
+
+	/*
+	 * Use the so called "secure" variant, which creates a unique inode
+	 * instead of reusing a single inode.  Each guest_memfd instance needs
+	 * its own inode to track the size, flags, etc.
+	 */
+	file = anon_inode_create_getfile(anon_name, &gunyah_gmem_fops, NULL,
+					 O_RDWR, NULL);
+	if (IS_ERR(file)) {
+		err = PTR_ERR(file);
+		goto err_fd;
+	}
+
+	file->f_flags |= O_LARGEFILE;
+
+	inode = file->f_inode;
+	WARN_ON(file->f_mapping != inode->i_mapping);
+
+	inode->i_private = (void *)(unsigned long)args->flags;
+	inode->i_mapping->a_ops = &gunyah_gmem_aops;
+	inode->i_mode |= S_IFREG;
+	inode->i_size = args->size;
+	mapping_set_gfp_mask(inode->i_mapping, GFP_HIGHUSER);
+	mapping_set_large_folios(inode->i_mapping);
+	mapping_set_unmovable(inode->i_mapping);
+	// mapping_set_release_always(inode->i_mapping);
+	/* Unmovable mappings are supposed to be marked unevictable as well. */
+	WARN_ON_ONCE(!mapping_unevictable(inode->i_mapping));
+
+	fd_install(fd, file);
+	return fd;
+
+err_fd:
+	put_unused_fd(fd);
+	return err;
+}
diff --git a/drivers/virt/gunyah/vm_mgr.c b/drivers/virt/gunyah/vm_mgr.c
index 9e402e6ea7fe..cd978d1ce93f 100644
--- a/drivers/virt/gunyah/vm_mgr.c
+++ b/drivers/virt/gunyah/vm_mgr.c
@@ -799,6 +799,15 @@ long gunyah_dev_vm_mgr_ioctl(struct gunyah_rm *rm, unsigned int cmd,
 	switch (cmd) {
 	case GUNYAH_CREATE_VM:
 		return gunyah_dev_ioctl_create_vm(rm, arg);
+	case GUNYAH_CREATE_GUEST_MEM: {
+		struct gunyah_create_mem_args args;
+
+		if (copy_from_user(&args, (const void __user *)arg,
+				   sizeof(args)))
+			return -EFAULT;
+
+		return gunyah_guest_mem_create(&args);
+	}
 	default:
 		return -ENOTTY;
 	}
diff --git a/drivers/virt/gunyah/vm_mgr.h b/drivers/virt/gunyah/vm_mgr.h
index 348dbeda57ec..d26693d10d22 100644
--- a/drivers/virt/gunyah/vm_mgr.h
+++ b/drivers/virt/gunyah/vm_mgr.h
@@ -77,4 +77,6 @@ void gunyah_vm_reclaim_memory(struct gunyah_vm *ghvm);
 
 int gunyah_vm_mmio_write(struct gunyah_vm *ghvm, u64 addr, u32 len, u64 data);
 
+int gunyah_guest_mem_create(struct gunyah_create_mem_args *args);
+
 #endif
diff --git a/include/uapi/linux/gunyah.h b/include/uapi/linux/gunyah.h
index 46f7d3aa61d0..c5f506350364 100644
--- a/include/uapi/linux/gunyah.h
+++ b/include/uapi/linux/gunyah.h
@@ -20,6 +20,25 @@
  */
 #define GUNYAH_CREATE_VM _IO(GUNYAH_IOCTL_TYPE, 0x0) /* Returns a Gunyah VM fd */
 
+enum gunyah_mem_flags {
+	GHMF_CLOEXEC = (1UL << 0),
+	GHMF_ALLOW_HUGEPAGE = (1UL << 1),
+};
+
+/**
+ * struct gunyah_create_mem_args - Description of guest memory to create
+ * @flags: See GHMF_*.
+ */
+struct gunyah_create_mem_args {
+	__u64 flags;
+	__u64 size;
+	__u64 reserved[6];
+};
+
+#define GUNYAH_CREATE_GUEST_MEM      \
+	_IOW(GUNYAH_IOCTL_TYPE, 0x8, \
+	     struct gunyah_create_mem_args) /* Returns a Gunyah memory fd */
+
 /*
  * ioctls for gunyah-vm fds (returned by GUNYAH_CREATE_VM)
  */

-- 
2.43.0