Re: [RFC PATCH v11 12/29] KVM: Add KVM_CREATE_GUEST_MEMFD ioctl() for guest-specific backing memory
From: Yuan Yao
Date: Fri Jul 21 2023 - 02:17:02 EST
On Tue, Jul 18, 2023 at 04:44:55PM -0700, Sean Christopherson wrote:
> TODO
>
> Cc: Fuad Tabba <tabba@xxxxxxxxxx>
> Cc: Vishal Annapurve <vannapurve@xxxxxxxxxx>
> Cc: Ackerley Tng <ackerleytng@xxxxxxxxxx>
> Cc: Jarkko Sakkinen <jarkko@xxxxxxxxxx>
> Cc: Maciej Szmigiero <mail@xxxxxxxxxxxxxxxxxxxxx>
> Cc: Vlastimil Babka <vbabka@xxxxxxx>
> Cc: David Hildenbrand <david@xxxxxxxxxx>
> Cc: Quentin Perret <qperret@xxxxxxxxxx>
> Cc: Michael Roth <michael.roth@xxxxxxx>
> Cc: Wang <wei.w.wang@xxxxxxxxx>
> Cc: Liam Merwick <liam.merwick@xxxxxxxxxx>
> Cc: Isaku Yamahata <isaku.yamahata@xxxxxxxxx>
> Co-developed-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
> Co-developed-by: Yu Zhang <yu.c.zhang@xxxxxxxxxxxxxxx>
> Signed-off-by: Yu Zhang <yu.c.zhang@xxxxxxxxxxxxxxx>
> Co-developed-by: Chao Peng <chao.p.peng@xxxxxxxxxxxxxxx>
> Signed-off-by: Chao Peng <chao.p.peng@xxxxxxxxxxxxxxx>
> Co-developed-by: Ackerley Tng <ackerleytng@xxxxxxxxxx>
> Signed-off-by: Ackerley Tng <ackerleytng@xxxxxxxxxx>
> Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>
> ---
> include/linux/kvm_host.h | 48 +++
> include/uapi/linux/kvm.h | 14 +-
> include/uapi/linux/magic.h | 1 +
> virt/kvm/Kconfig | 4 +
> virt/kvm/Makefile.kvm | 1 +
> virt/kvm/guest_mem.c | 591 +++++++++++++++++++++++++++++++++++++
> virt/kvm/kvm_main.c | 58 +++-
> virt/kvm/kvm_mm.h | 38 +++
> 8 files changed, 750 insertions(+), 5 deletions(-)
> create mode 100644 virt/kvm/guest_mem.c
>
> diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> index 97db63da6227..0d1e2ee8ae7a 100644
> --- a/include/linux/kvm_host.h
> +++ b/include/linux/kvm_host.h
> @@ -592,8 +592,20 @@ struct kvm_memory_slot {
> u32 flags;
> short id;
> u16 as_id;
> +
> +#ifdef CONFIG_KVM_PRIVATE_MEM
> + struct {
> + struct file __rcu *file;
> + pgoff_t pgoff;
> + } gmem;
> +#endif
> };
>
> +static inline bool kvm_slot_can_be_private(const struct kvm_memory_slot *slot)
> +{
> + return slot && (slot->flags & KVM_MEM_PRIVATE);
> +}
> +
> static inline bool kvm_slot_dirty_track_enabled(const struct kvm_memory_slot *slot)
> {
> return slot->flags & KVM_MEM_LOG_DIRTY_PAGES;
> @@ -688,6 +700,17 @@ static inline int kvm_arch_vcpu_memslots_id(struct kvm_vcpu *vcpu)
> }
> #endif
>
> +/*
> + * Arch code must define kvm_arch_has_private_mem if support for private memory
> + * is enabled.
> + */
> +#if !defined(kvm_arch_has_private_mem) && !IS_ENABLED(CONFIG_KVM_PRIVATE_MEM)
> +static inline bool kvm_arch_has_private_mem(struct kvm *kvm)
> +{
> + return false;
> +}
> +#endif
> +
> struct kvm_memslots {
> u64 generation;
> atomic_long_t last_used_slot;
> @@ -1380,6 +1403,7 @@ void *kvm_mmu_memory_cache_alloc(struct kvm_mmu_memory_cache *mc);
> void kvm_mmu_invalidate_begin(struct kvm *kvm);
> void kvm_mmu_invalidate_range_add(struct kvm *kvm, gfn_t start, gfn_t end);
> void kvm_mmu_invalidate_end(struct kvm *kvm);
> +bool kvm_mmu_unmap_gfn_range(struct kvm *kvm, struct kvm_gfn_range *range);
>
> long kvm_arch_dev_ioctl(struct file *filp,
> unsigned int ioctl, unsigned long arg);
> @@ -2313,6 +2337,30 @@ static inline unsigned long kvm_get_memory_attributes(struct kvm *kvm, gfn_t gfn
>
> bool kvm_arch_post_set_memory_attributes(struct kvm *kvm,
> struct kvm_gfn_range *range);
> +
> +static inline bool kvm_mem_is_private(struct kvm *kvm, gfn_t gfn)
> +{
> + return IS_ENABLED(CONFIG_KVM_PRIVATE_MEM) &&
> + kvm_get_memory_attributes(kvm, gfn) & KVM_MEMORY_ATTRIBUTE_PRIVATE;
> +}
> +#else
> +static inline bool kvm_mem_is_private(struct kvm *kvm, gfn_t gfn)
> +{
> + return false;
> +}
> #endif /* CONFIG_KVM_GENERIC_MEMORY_ATTRIBUTES */
>
> +#ifdef CONFIG_KVM_PRIVATE_MEM
> +int kvm_gmem_get_pfn(struct kvm *kvm, struct kvm_memory_slot *slot,
> + gfn_t gfn, kvm_pfn_t *pfn, int *max_order);
> +#else
> +static inline int kvm_gmem_get_pfn(struct kvm *kvm,
> + struct kvm_memory_slot *slot, gfn_t gfn,
> + kvm_pfn_t *pfn, int *max_order)
> +{
> + KVM_BUG_ON(1, kvm);
> + return -EIO;
> +}
> +#endif /* CONFIG_KVM_PRIVATE_MEM */
> +
> #endif
> diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
> index f065c57db327..9b344fc98598 100644
> --- a/include/uapi/linux/kvm.h
> +++ b/include/uapi/linux/kvm.h
> @@ -102,7 +102,10 @@ struct kvm_userspace_memory_region2 {
> __u64 guest_phys_addr;
> __u64 memory_size;
> __u64 userspace_addr;
> - __u64 pad[16];
> + __u64 gmem_offset;
> + __u32 gmem_fd;
> + __u32 pad1;
> + __u64 pad2[14];
> };
>
> /*
> @@ -112,6 +115,7 @@ struct kvm_userspace_memory_region2 {
> */
> #define KVM_MEM_LOG_DIRTY_PAGES (1UL << 0)
> #define KVM_MEM_READONLY (1UL << 1)
> +#define KVM_MEM_PRIVATE (1UL << 2)
>
> /* for KVM_IRQ_LINE */
> struct kvm_irq_level {
> @@ -2284,4 +2288,12 @@ struct kvm_memory_attributes {
>
> #define KVM_MEMORY_ATTRIBUTE_PRIVATE (1ULL << 3)
>
> +#define KVM_CREATE_GUEST_MEMFD _IOWR(KVMIO, 0xd4, struct kvm_create_guest_memfd)
> +
> +struct kvm_create_guest_memfd {
> + __u64 size;
> + __u64 flags;
> + __u64 reserved[6];
> +};
> +
> #endif /* __LINUX_KVM_H */
> diff --git a/include/uapi/linux/magic.h b/include/uapi/linux/magic.h
> index 6325d1d0e90f..15041aa7d9ae 100644
> --- a/include/uapi/linux/magic.h
> +++ b/include/uapi/linux/magic.h
> @@ -101,5 +101,6 @@
> #define DMA_BUF_MAGIC 0x444d4142 /* "DMAB" */
> #define DEVMEM_MAGIC 0x454d444d /* "DMEM" */
> #define SECRETMEM_MAGIC 0x5345434d /* "SECM" */
> +#define GUEST_MEMORY_MAGIC 0x474d454d /* "GMEM" */
>
> #endif /* __LINUX_MAGIC_H__ */
> diff --git a/virt/kvm/Kconfig b/virt/kvm/Kconfig
> index 8375bc49f97d..3ee3205e0b39 100644
> --- a/virt/kvm/Kconfig
> +++ b/virt/kvm/Kconfig
> @@ -103,3 +103,7 @@ config KVM_GENERIC_MMU_NOTIFIER
> config KVM_GENERIC_MEMORY_ATTRIBUTES
> select KVM_GENERIC_MMU_NOTIFIER
> bool
> +
> +config KVM_PRIVATE_MEM
> + select XARRAY_MULTI
> + bool
> diff --git a/virt/kvm/Makefile.kvm b/virt/kvm/Makefile.kvm
> index 2c27d5d0c367..a5a61bbe7f4c 100644
> --- a/virt/kvm/Makefile.kvm
> +++ b/virt/kvm/Makefile.kvm
> @@ -12,3 +12,4 @@ kvm-$(CONFIG_KVM_ASYNC_PF) += $(KVM)/async_pf.o
> kvm-$(CONFIG_HAVE_KVM_IRQ_ROUTING) += $(KVM)/irqchip.o
> kvm-$(CONFIG_HAVE_KVM_DIRTY_RING) += $(KVM)/dirty_ring.o
> kvm-$(CONFIG_HAVE_KVM_PFNCACHE) += $(KVM)/pfncache.o
> +kvm-$(CONFIG_KVM_PRIVATE_MEM) += $(KVM)/guest_mem.o
> diff --git a/virt/kvm/guest_mem.c b/virt/kvm/guest_mem.c
> new file mode 100644
> index 000000000000..1b705fd63fa8
> --- /dev/null
> +++ b/virt/kvm/guest_mem.c
> @@ -0,0 +1,591 @@
> +// SPDX-License-Identifier: GPL-2.0
> +#include <linux/backing-dev.h>
> +#include <linux/falloc.h>
> +#include <linux/kvm_host.h>
> +#include <linux/pagemap.h>
> +#include <linux/pseudo_fs.h>
> +
> +#include <uapi/linux/magic.h>
> +
> +#include "kvm_mm.h"
> +
> +static struct vfsmount *kvm_gmem_mnt;
> +
> +struct kvm_gmem {
> + struct kvm *kvm;
> + struct xarray bindings;
> + struct list_head entry;
> +};
> +
> +static struct folio *kvm_gmem_get_folio(struct file *file, pgoff_t index)
> +{
> + struct folio *folio;
> +
> + /* TODO: Support huge pages. */
> + folio = filemap_grab_folio(file->f_mapping, index);
> + if (!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.
> + *
> + * TODO: Skip clearing pages when trusted firmware will do it when
> + * assigning memory to the guest.
> + */
> + 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 void kvm_gmem_invalidate_begin(struct kvm_gmem *gmem, pgoff_t start,
> + pgoff_t end)
> +{
> + struct kvm_memory_slot *slot;
> + struct kvm *kvm = gmem->kvm;
> + unsigned long index;
> + bool flush = false;
> +
> + KVM_MMU_LOCK(kvm);
> +
> + kvm_mmu_invalidate_begin(kvm);
> +
> + xa_for_each_range(&gmem->bindings, index, slot, start, end - 1) {
> + pgoff_t pgoff = slot->gmem.pgoff;
> +
> + struct kvm_gfn_range gfn_range = {
> + .start = slot->base_gfn + max(pgoff, start) - pgoff,
> + .end = slot->base_gfn + min(pgoff + slot->npages, end) - pgoff,
> + .slot = slot,
> + .may_block = true,
> + };
> +
> + flush |= kvm_mmu_unmap_gfn_range(kvm, &gfn_range);
> + }
> +
> + if (flush)
> + kvm_flush_remote_tlbs(kvm);
> +
> + KVM_MMU_UNLOCK(kvm);
> +}
> +
> +static void kvm_gmem_invalidate_end(struct kvm_gmem *gmem, pgoff_t start,
> + pgoff_t end)
> +{
> + struct kvm *kvm = gmem->kvm;
> +
> + KVM_MMU_LOCK(kvm);
> + if (xa_find(&gmem->bindings, &start, end - 1, XA_PRESENT))
> + kvm_mmu_invalidate_end(kvm);
> + KVM_MMU_UNLOCK(kvm);
> +}
> +
> +static long kvm_gmem_punch_hole(struct inode *inode, loff_t offset, loff_t len)
> +{
> + struct list_head *gmem_list = &inode->i_mapping->private_list;
> + pgoff_t start = offset >> PAGE_SHIFT;
> + pgoff_t end = (offset + len) >> PAGE_SHIFT;
> + struct kvm_gmem *gmem;
> +
> + /*
> + * Bindings must stable across invalidation to ensure the start+end
> + * are balanced.
> + */
> + filemap_invalidate_lock(inode->i_mapping);
> +
> + list_for_each_entry(gmem, gmem_list, entry)
> + kvm_gmem_invalidate_begin(gmem, start, end);
> +
> + truncate_inode_pages_range(inode->i_mapping, offset, offset + len - 1);
> +
> + list_for_each_entry(gmem, gmem_list, entry)
> + kvm_gmem_invalidate_end(gmem, start, end);
> +
> + filemap_invalidate_unlock(inode->i_mapping);
> +
> + return 0;
> +}
> +
> +static long kvm_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 = kvm_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 kvm_gmem_fallocate(struct file *file, int mode, loff_t offset,
> + loff_t len)
> +{
> + int ret;
> +
> + if (!(mode & FALLOC_FL_KEEP_SIZE))
> + return -EOPNOTSUPP;
> +
> + if (mode & ~(FALLOC_FL_KEEP_SIZE | FALLOC_FL_PUNCH_HOLE))
> + return -EOPNOTSUPP;
> +
> + if (!PAGE_ALIGNED(offset) || !PAGE_ALIGNED(len))
> + return -EINVAL;
> +
> + if (mode & FALLOC_FL_PUNCH_HOLE)
> + ret = kvm_gmem_punch_hole(file_inode(file), offset, len);
> + else
> + ret = kvm_gmem_allocate(file_inode(file), offset, len);
> +
> + if (!ret)
> + file_modified(file);
> + return ret;
> +}
> +
> +static int kvm_gmem_release(struct inode *inode, struct file *file)
> +{
> + struct kvm_gmem *gmem = file->private_data;
> + struct kvm_memory_slot *slot;
> + struct kvm *kvm = gmem->kvm;
> + unsigned long index;
> +
> + filemap_invalidate_lock(inode->i_mapping);
> +
> + /*
> + * Prevent concurrent attempts to *unbind* a memslot. This is the last
> + * reference to the file and thus no new bindings can be created, but
> + * dereferencing the slot for existing bindings needs to be protected
> + * against memslot updates, specifically so that unbind doesn't race
> + * and free the memslot (kvm_gmem_get_file() will return NULL).
> + */
> + mutex_lock(&kvm->slots_lock);
> +
> + xa_for_each(&gmem->bindings, index, slot)
> + rcu_assign_pointer(slot->gmem.file, NULL);
> +
> + synchronize_rcu();
> +
> + /*
> + * All in-flight operations are gone and new bindings can be created.
> + * Zap all SPTEs pointed at by this file. Do not free the backing
> + * memory, as its lifetime is associated with the inode, not the file.
> + */
> + kvm_gmem_invalidate_begin(gmem, 0, -1ul);
> + kvm_gmem_invalidate_end(gmem, 0, -1ul);
> +
> + mutex_unlock(&kvm->slots_lock);
> +
> + list_del(&gmem->entry);
> +
> + filemap_invalidate_unlock(inode->i_mapping);
> +
> + xa_destroy(&gmem->bindings);
> + kfree(gmem);
> +
> + kvm_put_kvm(kvm);
> +
> + return 0;
> +}
> +
> +static struct file *kvm_gmem_get_file(struct kvm_memory_slot *slot)
> +{
> + struct file *file;
> +
> + rcu_read_lock();
> +
> + file = rcu_dereference(slot->gmem.file);
> + if (file && !get_file_rcu(file))
> + file = NULL;
> +
> + rcu_read_unlock();
> +
> + return file;
> +}
> +
> +static const struct file_operations kvm_gmem_fops = {
> + .open = generic_file_open,
> + .release = kvm_gmem_release,
> + .fallocate = kvm_gmem_fallocate,
> +};
> +
> +static int kvm_gmem_migrate_folio(struct address_space *mapping,
> + struct folio *dst, struct folio *src,
> + enum migrate_mode mode)
> +{
> + WARN_ON_ONCE(1);
> + return -EINVAL;
> +}
> +
> +static int kvm_gmem_error_page(struct address_space *mapping, struct page *page)
> +{
> + struct list_head *gmem_list = &mapping->private_list;
> + struct kvm_memory_slot *slot;
> + struct kvm_gmem *gmem;
> + unsigned long index;
> + pgoff_t start, end;
> + gfn_t gfn;
> +
> + filemap_invalidate_lock_shared(mapping);
> +
> + start = page->index;
> + end = start + thp_nr_pages(page);
> +
> + list_for_each_entry(gmem, gmem_list, entry) {
> + xa_for_each_range(&gmem->bindings, index, slot, start, end - 1) {
> + for (gfn = start; gfn < end; gfn++) {
Why the start end range used as gfn here ?
the page->index is offset of inode's page cache mapping and
gmem address space, IIUC, gfn calculation should follow same
way as kvm_gmem_invalidate_begin().
> + if (WARN_ON_ONCE(gfn < slot->base_gfn ||
> + gfn >= slot->base_gfn + slot->npages))
> + continue;
> +
> + /*
> + * FIXME: Tell userspace that the *private*
> + * memory encountered an error.
> + */
> + send_sig_mceerr(BUS_MCEERR_AR,
> + (void __user *)gfn_to_hva_memslot(slot, gfn),
> + PAGE_SHIFT, current);
> + }
> + }
> + }
> +
> + filemap_invalidate_unlock_shared(mapping);
> +
> + return 0;
> +}
> +
> +static const struct address_space_operations kvm_gmem_aops = {
> + .dirty_folio = noop_dirty_folio,
> +#ifdef CONFIG_MIGRATION
> + .migrate_folio = kvm_gmem_migrate_folio,
> +#endif
> + .error_remove_page = kvm_gmem_error_page,
> +};
> +
> +static int kvm_gmem_getattr(struct mnt_idmap *idmap,
> + const struct path *path, struct kstat *stat,
> + u32 request_mask, unsigned int query_flags)
> +{
> + struct inode *inode = path->dentry->d_inode;
> +
> + /* TODO */
> + generic_fillattr(idmap, inode, stat);
> + return 0;
> +}
> +
> +static int kvm_gmem_setattr(struct mnt_idmap *idmap, struct dentry *dentry,
> + struct iattr *attr)
> +{
> + /* TODO */
> + return -EINVAL;
> +}
> +static const struct inode_operations kvm_gmem_iops = {
> + .getattr = kvm_gmem_getattr,
> + .setattr = kvm_gmem_setattr,
> +};
> +
> +static int __kvm_gmem_create(struct kvm *kvm, loff_t size, struct vfsmount *mnt)
> +{
> + const char *anon_name = "[kvm-gmem]";
> + const struct qstr qname = QSTR_INIT(anon_name, strlen(anon_name));
> + struct kvm_gmem *gmem;
> + struct inode *inode;
> + struct file *file;
> + int fd, err;
> +
> + inode = alloc_anon_inode(mnt->mnt_sb);
> + if (IS_ERR(inode))
> + return PTR_ERR(inode);
> +
> + err = security_inode_init_security_anon(inode, &qname, NULL);
> + if (err)
> + goto err_inode;
> +
> + inode->i_private = (void *)(unsigned long)flags;
> + inode->i_op = &kvm_gmem_iops;
> + inode->i_mapping->a_ops = &kvm_gmem_aops;
> + inode->i_mode |= S_IFREG;
> + inode->i_size = size;
> + mapping_set_gfp_mask(inode->i_mapping, GFP_HIGHUSER);
> + mapping_set_unevictable(inode->i_mapping);
> + mapping_set_unmovable(inode->i_mapping);
> +
> + fd = get_unused_fd_flags(0);
> + if (fd < 0) {
> + err = fd;
> + goto err_inode;
> + }
> +
> + file = alloc_file_pseudo(inode, mnt, "kvm-gmem", O_RDWR, &kvm_gmem_fops);
> + if (IS_ERR(file)) {
> + err = PTR_ERR(file);
> + goto err_fd;
> + }
> +
> + file->f_flags |= O_LARGEFILE;
> + file->f_mapping = inode->i_mapping;
> +
> + gmem = kzalloc(sizeof(*gmem), GFP_KERNEL);
> + if (!gmem) {
> + err = -ENOMEM;
> + goto err_file;
> + }
> +
> + kvm_get_kvm(kvm);
> + gmem->kvm = kvm;
> + xa_init(&gmem->bindings);
> +
> + file->private_data = gmem;
> +
> + list_add(&gmem->entry, &inode->i_mapping->private_list);
> +
> + fd_install(fd, file);
> + return fd;
> +
> +err_file:
> + fput(file);
> +err_fd:
> + put_unused_fd(fd);
> +err_inode:
> + iput(inode);
> + return err;
> +}
> +
> +static bool kvm_gmem_is_valid_size(loff_t size, u64 flags)
> +{
> + if (size < 0 || !PAGE_ALIGNED(size))
> + return false;
> +
> + return true;
> +}
> +
> +int kvm_gmem_create(struct kvm *kvm, struct kvm_create_guest_memfd *args)
> +{
> + loff_t size = args->size;
> + u64 flags = args->flags;
> + u64 valid_flags = 0;
> +
> + if (flags & ~valid_flags)
> + return -EINVAL;
> +
> + if (!kvm_gmem_is_valid_size(size, flags))
> + return -EINVAL;
> +
> + return __kvm_gmem_create(kvm, size, flags, kvm_gmem_mnt);
> +}
> +
> +int kvm_gmem_bind(struct kvm *kvm, struct kvm_memory_slot *slot,
> + unsigned int fd, loff_t offset)
> +{
> + loff_t size = slot->npages << PAGE_SHIFT;
> + unsigned long start, end, flags;
> + struct kvm_gmem *gmem;
> + struct inode *inode;
> + struct file *file;
> +
> + BUILD_BUG_ON(sizeof(gfn_t) != sizeof(slot->gmem.pgoff));
> +
> + file = fget(fd);
> + if (!file)
> + return -EINVAL;
> +
> + if (file->f_op != &kvm_gmem_fops)
> + goto err;
> +
> + gmem = file->private_data;
> + if (gmem->kvm != kvm)
> + goto err;
> +
> + inode = file_inode(file);
> + flags = (unsigned long)inode->i_private;
> +
> + /*
> + * For simplicity, require the offset into the file and the size of the
> + * memslot to be aligned to the largest possible page size used to back
> + * the file (same as the size of the file itself).
> + */
> + if (!kvm_gmem_is_valid_size(offset, flags) ||
> + !kvm_gmem_is_valid_size(size, flags))
> + goto err;
> +
> + if (offset + size > i_size_read(inode))
> + goto err;
> +
> + filemap_invalidate_lock(inode->i_mapping);
> +
> + start = offset >> PAGE_SHIFT;
> + end = start + slot->npages;
> +
> + if (!xa_empty(&gmem->bindings) &&
> + xa_find(&gmem->bindings, &start, end - 1, XA_PRESENT)) {
> + filemap_invalidate_unlock(inode->i_mapping);
> + goto err;
> + }
> +
> + /*
> + * No synchronize_rcu() needed, any in-flight readers are guaranteed to
> + * be see either a NULL file or this new file, no need for them to go
> + * away.
> + */
> + rcu_assign_pointer(slot->gmem.file, file);
> + slot->gmem.pgoff = start;
> +
> + xa_store_range(&gmem->bindings, start, end - 1, slot, GFP_KERNEL);
> + filemap_invalidate_unlock(inode->i_mapping);
> +
> + /*
> + * Drop the reference to the file, even on success. The file pins KVM,
> + * not the other way 'round. Active bindings are invalidated if the
> + * file is closed before memslots are destroyed.
> + */
> + fput(file);
> + return 0;
> +
> +err:
> + fput(file);
> + return -EINVAL;
> +}
> +
> +void kvm_gmem_unbind(struct kvm_memory_slot *slot)
> +{
> + unsigned long start = slot->gmem.pgoff;
> + unsigned long end = start + slot->npages;
> + struct kvm_gmem *gmem;
> + struct file *file;
> +
> + /*
> + * Nothing to do if the underlying file was already closed (or is being
> + * closed right now), kvm_gmem_release() invalidates all bindings.
> + */
> + file = kvm_gmem_get_file(slot);
> + if (!file)
> + return;
> +
> + gmem = file->private_data;
> +
> + filemap_invalidate_lock(file->f_mapping);
> + xa_store_range(&gmem->bindings, start, end - 1, NULL, GFP_KERNEL);
> + rcu_assign_pointer(slot->gmem.file, NULL);
> + synchronize_rcu();
> + filemap_invalidate_unlock(file->f_mapping);
> +
> + fput(file);
> +}
> +
> +int kvm_gmem_get_pfn(struct kvm *kvm, struct kvm_memory_slot *slot,
> + gfn_t gfn, kvm_pfn_t *pfn, int *max_order)
> +{
> + pgoff_t index = gfn - slot->base_gfn + slot->gmem.pgoff;
> + struct kvm_gmem *gmem;
> + struct folio *folio;
> + struct page *page;
> + struct file *file;
> +
> + file = kvm_gmem_get_file(slot);
> + if (!file)
> + return -EFAULT;
> +
> + gmem = file->private_data;
> +
> + if (WARN_ON_ONCE(xa_load(&gmem->bindings, index) != slot)) {
> + fput(file);
> + return -EIO;
> + }
> +
> + folio = kvm_gmem_get_folio(file_inode(file), index);
> + if (!folio) {
> + fput(file);
> + return -ENOMEM;
> + }
> +
> + page = folio_file_page(folio, index);
> +
> + *pfn = page_to_pfn(page);
> + *max_order = compound_order(compound_head(page));
> +
> + folio_unlock(folio);
> + fput(file);
> +
> + return 0;
> +}
> +EXPORT_SYMBOL_GPL(kvm_gmem_get_pfn);
> +
> +static int kvm_gmem_init_fs_context(struct fs_context *fc)
> +{
> + if (!init_pseudo(fc, GUEST_MEMORY_MAGIC))
> + return -ENOMEM;
> +
> + return 0;
> +}
> +
> +static struct file_system_type kvm_gmem_fs = {
> + .name = "kvm_guest_memory",
> + .init_fs_context = kvm_gmem_init_fs_context,
> + .kill_sb = kill_anon_super,
> +};
> +
> +int kvm_gmem_init(void)
> +{
> + kvm_gmem_mnt = kern_mount(&kvm_gmem_fs);
> + if (IS_ERR(kvm_gmem_mnt))
> + return PTR_ERR(kvm_gmem_mnt);
> +
> + /* For giggles. Userspace can never map this anyways. */
> + kvm_gmem_mnt->mnt_flags |= MNT_NOEXEC;
> +
> + return 0;
> +}
> +
> +void kvm_gmem_exit(void)
> +{
> + kern_unmount(kvm_gmem_mnt);
> + kvm_gmem_mnt = NULL;
> +}
> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> index 1a31bfa025b0..a8686e8473a4 100644
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> @@ -761,7 +761,7 @@ void kvm_mmu_invalidate_range_add(struct kvm *kvm, gfn_t start, gfn_t end)
> }
> }
>
> -static bool kvm_mmu_unmap_gfn_range(struct kvm *kvm, struct kvm_gfn_range *range)
> +bool kvm_mmu_unmap_gfn_range(struct kvm *kvm, struct kvm_gfn_range *range)
> {
> kvm_mmu_invalidate_range_add(kvm, range->start, range->end);
> return kvm_unmap_gfn_range(kvm, range);
> @@ -992,6 +992,9 @@ static void kvm_destroy_dirty_bitmap(struct kvm_memory_slot *memslot)
> /* This does not remove the slot from struct kvm_memslots data structures */
> static void kvm_free_memslot(struct kvm *kvm, struct kvm_memory_slot *slot)
> {
> + if (slot->flags & KVM_MEM_PRIVATE)
> + kvm_gmem_unbind(slot);
> +
> kvm_destroy_dirty_bitmap(slot);
>
> kvm_arch_free_memslot(kvm, slot);
> @@ -1556,10 +1559,18 @@ static void kvm_replace_memslot(struct kvm *kvm,
> }
> }
>
> -static int check_memory_region_flags(const struct kvm_userspace_memory_region2 *mem)
> +static int check_memory_region_flags(struct kvm *kvm,
> + const struct kvm_userspace_memory_region2 *mem)
> {
> u32 valid_flags = KVM_MEM_LOG_DIRTY_PAGES;
>
> + if (kvm_arch_has_private_mem(kvm))
> + valid_flags |= KVM_MEM_PRIVATE;
> +
> + /* Dirty logging private memory is not currently supported. */
> + if (mem->flags & KVM_MEM_PRIVATE)
> + valid_flags &= ~KVM_MEM_LOG_DIRTY_PAGES;
> +
> #ifdef __KVM_HAVE_READONLY_MEM
> valid_flags |= KVM_MEM_READONLY;
> #endif
> @@ -1968,7 +1979,7 @@ int __kvm_set_memory_region(struct kvm *kvm,
> int as_id, id;
> int r;
>
> - r = check_memory_region_flags(mem);
> + r = check_memory_region_flags(kvm, mem);
> if (r)
> return r;
>
> @@ -1987,6 +1998,10 @@ int __kvm_set_memory_region(struct kvm *kvm,
> !access_ok((void __user *)(unsigned long)mem->userspace_addr,
> mem->memory_size))
> return -EINVAL;
> + if (mem->flags & KVM_MEM_PRIVATE &&
> + (mem->gmem_offset & (PAGE_SIZE - 1) ||
> + mem->gmem_offset + mem->memory_size < mem->gmem_offset))
> + return -EINVAL;
> if (as_id >= KVM_ADDRESS_SPACE_NUM || id >= KVM_MEM_SLOTS_NUM)
> return -EINVAL;
> if (mem->guest_phys_addr + mem->memory_size < mem->guest_phys_addr)
> @@ -2025,6 +2040,9 @@ int __kvm_set_memory_region(struct kvm *kvm,
> if ((kvm->nr_memslot_pages + npages) < kvm->nr_memslot_pages)
> return -EINVAL;
> } else { /* Modify an existing slot. */
> + /* Private memslots are immutable, they can only be deleted. */
> + if (mem->flags & KVM_MEM_PRIVATE)
> + return -EINVAL;
> if ((mem->userspace_addr != old->userspace_addr) ||
> (npages != old->npages) ||
> ((mem->flags ^ old->flags) & KVM_MEM_READONLY))
> @@ -2053,10 +2071,23 @@ int __kvm_set_memory_region(struct kvm *kvm,
> new->npages = npages;
> new->flags = mem->flags;
> new->userspace_addr = mem->userspace_addr;
> + if (mem->flags & KVM_MEM_PRIVATE) {
> + r = kvm_gmem_bind(kvm, new, mem->gmem_fd, mem->gmem_offset);
> + if (r)
> + goto out;
> + }
>
> r = kvm_set_memslot(kvm, old, new, change);
> if (r)
> - kfree(new);
> + goto out_restricted;
> +
> + return 0;
> +
> +out_restricted:
> + if (mem->flags & KVM_MEM_PRIVATE)
> + kvm_gmem_unbind(new);
> +out:
> + kfree(new);
> return r;
> }
> EXPORT_SYMBOL_GPL(__kvm_set_memory_region);
> @@ -2356,6 +2387,8 @@ static int kvm_vm_ioctl_clear_dirty_log(struct kvm *kvm,
> #ifdef CONFIG_KVM_GENERIC_MEMORY_ATTRIBUTES
> static u64 kvm_supported_mem_attributes(struct kvm *kvm)
> {
> + if (kvm_arch_has_private_mem(kvm))
> + return KVM_MEMORY_ATTRIBUTE_PRIVATE;
> return 0;
> }
>
> @@ -5134,6 +5167,16 @@ static long kvm_vm_ioctl(struct file *filp,
> case KVM_GET_STATS_FD:
> r = kvm_vm_ioctl_get_stats_fd(kvm);
> break;
> + case KVM_CREATE_GUEST_MEMFD: {
> + struct kvm_create_guest_memfd guest_memfd;
> +
> + r = -EFAULT;
> + if (copy_from_user(&guest_memfd, argp, sizeof(guest_memfd)))
> + goto out;
> +
> + r = kvm_gmem_create(kvm, &guest_memfd);
> + break;
> + }
> default:
> r = kvm_arch_vm_ioctl(filp, ioctl, arg);
> }
> @@ -6255,12 +6298,17 @@ int kvm_init(unsigned vcpu_size, unsigned vcpu_align, struct module *module)
> if (r)
> goto err_async_pf;
>
> + r = kvm_gmem_init();
> + if (r)
> + goto err_gmem;
> +
> kvm_chardev_ops.owner = module;
>
> kvm_preempt_ops.sched_in = kvm_sched_in;
> kvm_preempt_ops.sched_out = kvm_sched_out;
>
> kvm_init_debug();
> + kvm_gmem_init();
>
> r = kvm_vfio_ops_init();
> if (WARN_ON_ONCE(r))
> @@ -6281,6 +6329,8 @@ int kvm_init(unsigned vcpu_size, unsigned vcpu_align, struct module *module)
> err_register:
> kvm_vfio_ops_exit();
> err_vfio:
> + kvm_gmem_exit();
> +err_gmem:
> kvm_async_pf_deinit();
> err_async_pf:
> kvm_irqfd_exit();
> diff --git a/virt/kvm/kvm_mm.h b/virt/kvm/kvm_mm.h
> index 180f1a09e6ba..798f20d612bb 100644
> --- a/virt/kvm/kvm_mm.h
> +++ b/virt/kvm/kvm_mm.h
> @@ -37,4 +37,42 @@ static inline void gfn_to_pfn_cache_invalidate_start(struct kvm *kvm,
> }
> #endif /* HAVE_KVM_PFNCACHE */
>
> +#ifdef CONFIG_KVM_PRIVATE_MEM
> +int kvm_gmem_init(void);
> +void kvm_gmem_exit(void);
> +int kvm_gmem_create(struct kvm *kvm, struct kvm_create_guest_memfd *args);
> +int kvm_gmem_bind(struct kvm *kvm, struct kvm_memory_slot *slot,
> + unsigned int fd, loff_t offset);
> +void kvm_gmem_unbind(struct kvm_memory_slot *slot);
> +#else
> +static inline int kvm_gmem_init(void)
> +{
> + return 0;
> +}
> +
> +static inline void kvm_gmem_exit(void)
> +{
> +
> +}
> +
> +static inline int kvm_gmem_create(struct kvm *kvm,
> + struct kvm_create_guest_memfd *args)
> +{
> + return -EOPNOTSUPP;
> +}
> +
> +static inline int kvm_gmem_bind(struct kvm *kvm,
> + struct kvm_memory_slot *slot,
> + unsigned int fd, loff_t offset)
> +{
> + WARN_ON_ONCE(1);
> + return -EIO;
> +}
> +
> +static inline void kvm_gmem_unbind(struct kvm_memory_slot *slot)
> +{
> + WARN_ON_ONCE(1);
> +}
> +#endif /* CONFIG_KVM_PRIVATE_MEM */
> +
> #endif /* __KVM_MM_H__ */
> --
> 2.41.0.255.g8b1d071c50-goog
>