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Message-ID: <ZzVAzc3rVTW9OCJP@google.com>
Date: Wed, 13 Nov 2024 16:14:05 -0800
From: Sean Christopherson <seanjc@...gle.com>
To: Paolo Bonzini <pbonzini@...hat.com>
Cc: linux-kernel@...r.kernel.org, kvm@...r.kernel.org, michael.roth@....com
Subject: Re: [PATCH 1/3] KVM: gmem: allocate private data for the gmem inode
+Ackerley, who's also working on resurrecting the file system[*]. At a glance,
there appear to be non-trivial differences, e.g. Ackerley's version has a call
to security_inode_init_security_anon(). I've paged out much of the inode stuff,
so I trust Ackerley's judgment far, far more than my own :-)
[*] https://lore.kernel.org/all/d1940d466fc69472c8b6dda95df2e0522b2d8744.1726009989.git.ackerleytng@google.com
On Fri, Nov 08, 2024, Paolo Bonzini wrote:
> In preparation for removing the usage of the uptodate flag,
> reintroduce the gmem filesystem type. We need it in order to
> free the private inode information.
>
> Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
> ---
> include/uapi/linux/magic.h | 1 +
> virt/kvm/guest_memfd.c | 117 +++++++++++++++++++++++++++++++++----
> virt/kvm/kvm_main.c | 7 ++-
> virt/kvm/kvm_mm.h | 8 ++-
> 4 files changed, 119 insertions(+), 14 deletions(-)
>
> diff --git a/include/uapi/linux/magic.h b/include/uapi/linux/magic.h
> index bb575f3ab45e..d856dd6a7ed9 100644
> --- a/include/uapi/linux/magic.h
> +++ b/include/uapi/linux/magic.h
> @@ -103,5 +103,6 @@
> #define DEVMEM_MAGIC 0x454d444d /* "DMEM" */
> #define SECRETMEM_MAGIC 0x5345434d /* "SECM" */
> #define PID_FS_MAGIC 0x50494446 /* "PIDF" */
> +#define KVM_GUEST_MEM_MAGIC 0x474d454d /* "GMEM" */
>
> #endif /* __LINUX_MAGIC_H__ */
> diff --git a/virt/kvm/guest_memfd.c b/virt/kvm/guest_memfd.c
> index 8f079a61a56d..3ea5a7597fd4 100644
> --- a/virt/kvm/guest_memfd.c
> +++ b/virt/kvm/guest_memfd.c
> @@ -4,9 +4,74 @@
> #include <linux/kvm_host.h>
> #include <linux/pagemap.h>
> #include <linux/anon_inodes.h>
> +#include <linux/pseudo_fs.h>
>
> #include "kvm_mm.h"
>
> +/* Do all the filesystem crap just for evict_inode... */
> +
> +static struct vfsmount *kvm_gmem_mnt __read_mostly;
> +
> +static void gmem_evict_inode(struct inode *inode)
> +{
> + kvfree(inode->i_private);
> + truncate_inode_pages_final(&inode->i_data);
> + clear_inode(inode);
> +}
> +
> +static const struct super_operations gmem_super_operations = {
> + .drop_inode = generic_delete_inode,
> + .evict_inode = gmem_evict_inode,
> + .statfs = simple_statfs,
> +};
> +
> +static int gmem_init_fs_context(struct fs_context *fc)
> +{
> + struct pseudo_fs_context *ctx = init_pseudo(fc, KVM_GUEST_MEM_MAGIC);
> + if (!ctx)
> + return -ENOMEM;
> +
> + ctx->ops = &gmem_super_operations;
> + return 0;
> +}
> +
> +static struct file_system_type kvm_gmem_fs_type = {
> + .name = "kvm_gmemfs",
> + .init_fs_context = gmem_init_fs_context,
> + .kill_sb = kill_anon_super,
> +};
> +
> +static struct file *kvm_gmem_create_file(const char *name, const struct file_operations *fops)
> +{
> + struct inode *inode;
> + struct file *file;
> +
> + if (fops->owner && !try_module_get(fops->owner))
> + return ERR_PTR(-ENOENT);
> +
> + inode = alloc_anon_inode(kvm_gmem_mnt->mnt_sb);
> + if (IS_ERR(inode)) {
> + file = ERR_CAST(inode);
> + goto err;
> + }
> + file = alloc_file_pseudo(inode, kvm_gmem_mnt, name, O_RDWR, fops);
> + if (IS_ERR(file))
> + goto err_iput;
> +
> + return file;
> +
> +err_iput:
> + iput(inode);
> +err:
> + module_put(fops->owner);
> + return file;
> +}
> +
> +
> +struct kvm_gmem_inode {
> + unsigned long flags;
> +};
> +
> struct kvm_gmem {
> struct kvm *kvm;
> struct xarray bindings;
> @@ -308,9 +373,31 @@ static struct file_operations kvm_gmem_fops = {
> .fallocate = kvm_gmem_fallocate,
> };
>
> -void kvm_gmem_init(struct module *module)
> +int kvm_gmem_init(struct module *module)
> {
> + int ret;
> +
> + ret = register_filesystem(&kvm_gmem_fs_type);
> + if (ret) {
> + pr_err("kvm-gmem: cannot register file system (%d)\n", ret);
> + return ret;
> + }
> +
> + kvm_gmem_mnt = kern_mount(&kvm_gmem_fs_type);
> + if (IS_ERR(kvm_gmem_mnt)) {
> + pr_err("kvm-gmem: kernel mount failed (%ld)\n", PTR_ERR(kvm_gmem_mnt));
> + return PTR_ERR(kvm_gmem_mnt);
> + }
> +
> kvm_gmem_fops.owner = module;
> +
> + return 0;
> +}
> +
> +void kvm_gmem_exit(void)
> +{
> + kern_unmount(kvm_gmem_mnt);
> + unregister_filesystem(&kvm_gmem_fs_type);
> }
>
> static int kvm_gmem_migrate_folio(struct address_space *mapping,
> @@ -394,15 +481,23 @@ static const struct inode_operations kvm_gmem_iops = {
>
> static int __kvm_gmem_create(struct kvm *kvm, loff_t size, u64 flags)
> {
> - const char *anon_name = "[kvm-gmem]";
> + const char *gmem_name = "[kvm-gmem]";
> + struct kvm_gmem_inode *i_gmem;
> struct kvm_gmem *gmem;
> struct inode *inode;
> struct file *file;
> int fd, err;
>
> + i_gmem = kvzalloc(sizeof(struct kvm_gmem_inode), GFP_KERNEL);
> + if (!i_gmem)
> + return -ENOMEM;
> + i_gmem->flags = flags;
> +
> fd = get_unused_fd_flags(0);
> - if (fd < 0)
> - return fd;
> + if (fd < 0) {
> + err = fd;
> + goto err_i_gmem;
> + }
>
> gmem = kzalloc(sizeof(*gmem), GFP_KERNEL);
> if (!gmem) {
> @@ -410,19 +505,19 @@ static int __kvm_gmem_create(struct kvm *kvm, loff_t size, u64 flags)
> goto err_fd;
> }
>
> - file = anon_inode_create_getfile(anon_name, &kvm_gmem_fops, gmem,
> - O_RDWR, NULL);
> + file = kvm_gmem_create_file(gmem_name, &kvm_gmem_fops);
> if (IS_ERR(file)) {
> err = PTR_ERR(file);
> goto err_gmem;
> }
>
> + inode = file->f_inode;
> +
> + file->f_mapping = inode->i_mapping;
> + file->private_data = gmem;
> file->f_flags |= O_LARGEFILE;
>
> - inode = file->f_inode;
> - WARN_ON(file->f_mapping != inode->i_mapping);
> -
> - inode->i_private = (void *)(unsigned long)flags;
> + inode->i_private = i_gmem;
> inode->i_op = &kvm_gmem_iops;
> inode->i_mapping->a_ops = &kvm_gmem_aops;
> inode->i_mode |= S_IFREG;
> @@ -444,6 +539,8 @@ static int __kvm_gmem_create(struct kvm *kvm, loff_t size, u64 flags)
> kfree(gmem);
> err_fd:
> put_unused_fd(fd);
> +err_i_gmem:
> + kvfree(i_gmem);
> return err;
> }
>
> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> index 279e03029ce1..8b7b4e0eb639 100644
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> @@ -6504,7 +6504,9 @@ int kvm_init(unsigned vcpu_size, unsigned vcpu_align, struct module *module)
> if (WARN_ON_ONCE(r))
> goto err_vfio;
>
> - kvm_gmem_init(module);
> + r = kvm_gmem_init(module);
> + if (r)
> + goto err_gmem;
>
> r = kvm_init_virtualization();
> if (r)
> @@ -6525,6 +6527,8 @@ int kvm_init(unsigned vcpu_size, unsigned vcpu_align, struct module *module)
> err_register:
> kvm_uninit_virtualization();
> err_virt:
> + kvm_gmem_exit();
> +err_gmem:
> kvm_vfio_ops_exit();
> err_vfio:
> kvm_async_pf_deinit();
> @@ -6556,6 +6560,7 @@ void kvm_exit(void)
> for_each_possible_cpu(cpu)
> free_cpumask_var(per_cpu(cpu_kick_mask, cpu));
> kmem_cache_destroy(kvm_vcpu_cache);
> + kvm_gmem_exit();
> kvm_vfio_ops_exit();
> kvm_async_pf_deinit();
> kvm_irqfd_exit();
> diff --git a/virt/kvm/kvm_mm.h b/virt/kvm/kvm_mm.h
> index 715f19669d01..91e4202574a8 100644
> --- a/virt/kvm/kvm_mm.h
> +++ b/virt/kvm/kvm_mm.h
> @@ -36,15 +36,17 @@ static inline void gfn_to_pfn_cache_invalidate_start(struct kvm *kvm,
> #endif /* HAVE_KVM_PFNCACHE */
>
> #ifdef CONFIG_KVM_PRIVATE_MEM
> -void kvm_gmem_init(struct module *module);
> +int kvm_gmem_init(struct module *module);
> +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 void kvm_gmem_init(struct module *module)
> +static inline void kvm_gmem_exit(void) {}
> +static inline int kvm_gmem_init(struct module *module)
> {
> -
> + return 0;
> }
>
> static inline int kvm_gmem_bind(struct kvm *kvm,
> --
> 2.43.5
>
>
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