Message-ID: <dd948073-0839-4f75-8cec-1f3041231ed7@amd.com>
Date: Wed, 8 Oct 2025 10:55:46 +0530
From: "Garg, Shivank" <shivankg@....com>
To: Sean Christopherson <seanjc@...gle.com>, Marc Zyngier <maz@...nel.org>,
 Oliver Upton <oliver.upton@...ux.dev>, Paolo Bonzini <pbonzini@...hat.com>
Cc: linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.linux.dev,
 kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
 David Hildenbrand <david@...hat.com>, Fuad Tabba <tabba@...gle.com>,
 Ackerley Tng <ackerleytng@...gle.com>, Ashish Kalra <ashish.kalra@....com>,
 Vlastimil Babka <vbabka@...e.cz>
Subject: Re: [PATCH v12 01/12] KVM: guest_memfd: Rename "struct kvm_gmem" to
 "struct gmem_file"



On 10/8/2025 3:44 AM, Sean Christopherson wrote:
> Rename the "kvm_gmem" structure to "gmem_file" in anticipation of using
> dedicated guest_memfd inodes instead of anonyomous inodes, at which point
> the "kvm_gmem" nomenclature becomes quite misleading.  In guest_memfd,
> inodes are effectively the raw underlying physical storage, and will be
> used to track properties of the physical memory, while each gmem file is
> effectively a single VM's view of that storage, and is used to track assets
> specific to its associated VM, e.g. memslots=>gmem bindings.
> 
> Using "kvm_gmem" suggests that the per-VM/per-file structures are _the_
> guest_memfd instance, which almost the exact opposite of reality.
> 
> Opportunistically rename local variables from "gmem" to "f", again to
> avoid confusion once guest_memfd specific inodes come along.
> 
> No functional change intended.
> 
> Signed-off-by: Sean Christopherson <seanjc@...gle.com>
> ---
>  virt/kvm/guest_memfd.c | 100 ++++++++++++++++++++++-------------------
>  1 file changed, 54 insertions(+), 46 deletions(-)
> 
> diff --git a/virt/kvm/guest_memfd.c b/virt/kvm/guest_memfd.c
> index fbca8c0972da..3c57fb42f12c 100644
> --- a/virt/kvm/guest_memfd.c
> +++ b/virt/kvm/guest_memfd.c
> @@ -7,7 +7,16 @@
>  
>  #include "kvm_mm.h"
>  
> -struct kvm_gmem {
> +/*
> + * A guest_memfd instance can be associated multiple VMs, each with its own
> + * "view" of the underlying physical memory.
> + *
> + * The gmem's inode is effectively the raw underlying physical storage, and is
> + * used to track properties of the physical memory, while each gmem file is
> + * effectively a single VM's view of that storage, and is used to track assets
> + * specific to its associated VM, e.g. memslots=>gmem bindings.
> + */
> +struct gmem_file {
>  	struct kvm *kvm;
>  	struct xarray bindings;
>  	struct list_head entry;
> @@ -110,16 +119,16 @@ static enum kvm_gfn_range_filter kvm_gmem_get_invalidate_filter(struct inode *in
>  	return KVM_FILTER_PRIVATE;
>  }
>  
> -static void __kvm_gmem_invalidate_begin(struct kvm_gmem *gmem, pgoff_t start,
> +static void __kvm_gmem_invalidate_begin(struct gmem_file *f, pgoff_t start,
>  					pgoff_t end,
>  					enum kvm_gfn_range_filter attr_filter)
>  {
>  	bool flush = false, found_memslot = false;
>  	struct kvm_memory_slot *slot;
> -	struct kvm *kvm = gmem->kvm;
> +	struct kvm *kvm = f->kvm;
>  	unsigned long index;
>  
> -	xa_for_each_range(&gmem->bindings, index, slot, start, end - 1) {
> +	xa_for_each_range(&f->bindings, index, slot, start, end - 1) {
>  		pgoff_t pgoff = slot->gmem.pgoff;
>  
>  		struct kvm_gfn_range gfn_range = {
> @@ -152,20 +161,20 @@ static void kvm_gmem_invalidate_begin(struct inode *inode, pgoff_t start,
>  {
>  	struct list_head *gmem_list = &inode->i_mapping->i_private_list;
>  	enum kvm_gfn_range_filter attr_filter;
> -	struct kvm_gmem *gmem;
> +	struct gmem_file *f;
>  
>  	attr_filter = kvm_gmem_get_invalidate_filter(inode);
>  
> -	list_for_each_entry(gmem, gmem_list, entry)
> -		__kvm_gmem_invalidate_begin(gmem, start, end, attr_filter);
> +	list_for_each_entry(f, gmem_list, entry)
> +		__kvm_gmem_invalidate_begin(f, start, end, attr_filter);
>  }
>  
> -static void __kvm_gmem_invalidate_end(struct kvm_gmem *gmem, pgoff_t start,
> +static void __kvm_gmem_invalidate_end(struct gmem_file *f, pgoff_t start,
>  				      pgoff_t end)
>  {
> -	struct kvm *kvm = gmem->kvm;
> +	struct kvm *kvm = f->kvm;
>  
> -	if (xa_find(&gmem->bindings, &start, end - 1, XA_PRESENT)) {
> +	if (xa_find(&f->bindings, &start, end - 1, XA_PRESENT)) {
>  		KVM_MMU_LOCK(kvm);
>  		kvm_mmu_invalidate_end(kvm);
>  		KVM_MMU_UNLOCK(kvm);
> @@ -176,10 +185,10 @@ static void kvm_gmem_invalidate_end(struct inode *inode, pgoff_t start,
>  				    pgoff_t end)
>  {
>  	struct list_head *gmem_list = &inode->i_mapping->i_private_list;
> -	struct kvm_gmem *gmem;
> +	struct gmem_file *f;
>  
> -	list_for_each_entry(gmem, gmem_list, entry)
> -		__kvm_gmem_invalidate_end(gmem, start, end);
> +	list_for_each_entry(f, gmem_list, entry)
> +		__kvm_gmem_invalidate_end(f, start, end);
>  }
>  
>  static long kvm_gmem_punch_hole(struct inode *inode, loff_t offset, loff_t len)
> @@ -277,9 +286,9 @@ static long kvm_gmem_fallocate(struct file *file, int mode, loff_t offset,
>  
>  static int kvm_gmem_release(struct inode *inode, struct file *file)
>  {
> -	struct kvm_gmem *gmem = file->private_data;
> +	struct gmem_file *f = file->private_data;
>  	struct kvm_memory_slot *slot;
> -	struct kvm *kvm = gmem->kvm;
> +	struct kvm *kvm = f->kvm;
>  	unsigned long index;
>  
>  	/*
> @@ -299,7 +308,7 @@ static int kvm_gmem_release(struct inode *inode, struct file *file)
>  
>  	filemap_invalidate_lock(inode->i_mapping);
>  
> -	xa_for_each(&gmem->bindings, index, slot)
> +	xa_for_each(&f->bindings, index, slot)
>  		WRITE_ONCE(slot->gmem.file, NULL);
>  
>  	/*
> @@ -307,18 +316,18 @@ static int kvm_gmem_release(struct inode *inode, struct file *file)
>  	 * 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_begin(f, 0, -1ul,
>  				    kvm_gmem_get_invalidate_filter(inode));
> -	__kvm_gmem_invalidate_end(gmem, 0, -1ul);
> +	__kvm_gmem_invalidate_end(f, 0, -1ul);
>  
> -	list_del(&gmem->entry);
> +	list_del(&f->entry);
>  
>  	filemap_invalidate_unlock(inode->i_mapping);
>  
>  	mutex_unlock(&kvm->slots_lock);
>  
> -	xa_destroy(&gmem->bindings);
> -	kfree(gmem);
> +	xa_destroy(&f->bindings);
> +	kfree(f);
>  
>  	kvm_put_kvm(kvm);
>  
> @@ -493,7 +502,7 @@ bool __weak kvm_arch_supports_gmem_init_shared(struct kvm *kvm)
>  static int __kvm_gmem_create(struct kvm *kvm, loff_t size, u64 flags)
>  {
>  	const char *anon_name = "[kvm-gmem]";
> -	struct kvm_gmem *gmem;
> +	struct gmem_file *f;
>  	struct inode *inode;
>  	struct file *file;
>  	int fd, err;
> @@ -502,14 +511,13 @@ static int __kvm_gmem_create(struct kvm *kvm, loff_t size, u64 flags)
>  	if (fd < 0)
>  		return fd;
>  
> -	gmem = kzalloc(sizeof(*gmem), GFP_KERNEL);
> -	if (!gmem) {
> +	f = kzalloc(sizeof(*f), GFP_KERNEL);
> +	if (!f) {
>  		err = -ENOMEM;
>  		goto err_fd;
>  	}
>  
> -	file = anon_inode_create_getfile(anon_name, &kvm_gmem_fops, gmem,
> -					 O_RDWR, NULL);
> +	file = anon_inode_create_getfile(anon_name, &kvm_gmem_fops, f, O_RDWR, NULL);
>  	if (IS_ERR(file)) {
>  		err = PTR_ERR(file);
>  		goto err_gmem;
> @@ -531,15 +539,15 @@ static int __kvm_gmem_create(struct kvm *kvm, loff_t size, u64 flags)
>  	WARN_ON_ONCE(!mapping_unevictable(inode->i_mapping));
>  
>  	kvm_get_kvm(kvm);
> -	gmem->kvm = kvm;
> -	xa_init(&gmem->bindings);
> -	list_add(&gmem->entry, &inode->i_mapping->i_private_list);
> +	f->kvm = kvm;
> +	xa_init(&f->bindings);
> +	list_add(&f->entry, &inode->i_mapping->i_private_list);
>  
>  	fd_install(fd, file);
>  	return fd;
>  
>  err_gmem:
> -	kfree(gmem);
> +	kfree(f);
>  err_fd:
>  	put_unused_fd(fd);
>  	return err;
> @@ -564,7 +572,7 @@ int kvm_gmem_bind(struct kvm *kvm, struct kvm_memory_slot *slot,
>  {
>  	loff_t size = slot->npages << PAGE_SHIFT;
>  	unsigned long start, end;
> -	struct kvm_gmem *gmem;
> +	struct gmem_file *f;
>  	struct inode *inode;
>  	struct file *file;
>  	int r = -EINVAL;
> @@ -578,8 +586,8 @@ int kvm_gmem_bind(struct kvm *kvm, struct kvm_memory_slot *slot,
>  	if (file->f_op != &kvm_gmem_fops)
>  		goto err;
>  
> -	gmem = file->private_data;
> -	if (gmem->kvm != kvm)
> +	f = file->private_data;
> +	if (f->kvm != kvm)
>  		goto err;
>  
>  	inode = file_inode(file);
> @@ -593,8 +601,8 @@ int kvm_gmem_bind(struct kvm *kvm, struct kvm_memory_slot *slot,
>  	start = offset >> PAGE_SHIFT;
>  	end = start + slot->npages;
>  
> -	if (!xa_empty(&gmem->bindings) &&
> -	    xa_find(&gmem->bindings, &start, end - 1, XA_PRESENT)) {
> +	if (!xa_empty(&f->bindings) &&
> +	    xa_find(&f->bindings, &start, end - 1, XA_PRESENT)) {
>  		filemap_invalidate_unlock(inode->i_mapping);
>  		goto err;
>  	}
> @@ -609,7 +617,7 @@ int kvm_gmem_bind(struct kvm *kvm, struct kvm_memory_slot *slot,
>  	if (kvm_gmem_supports_mmap(inode))
>  		slot->flags |= KVM_MEMSLOT_GMEM_ONLY;
>  
> -	xa_store_range(&gmem->bindings, start, end - 1, slot, GFP_KERNEL);
> +	xa_store_range(&f->bindings, start, end - 1, slot, GFP_KERNEL);
>  	filemap_invalidate_unlock(inode->i_mapping);
>  
>  	/*
> @@ -627,7 +635,7 @@ 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 gmem_file *f;
>  	struct file *file;
>  
>  	/*
> @@ -638,10 +646,10 @@ void kvm_gmem_unbind(struct kvm_memory_slot *slot)
>  	if (!file)
>  		return;
>  
> -	gmem = file->private_data;
> +	f = file->private_data;
>  
>  	filemap_invalidate_lock(file->f_mapping);
> -	xa_store_range(&gmem->bindings, start, end - 1, NULL, GFP_KERNEL);
> +	xa_store_range(&f->bindings, start, end - 1, NULL, GFP_KERNEL);
>  
>  	/*
>  	 * synchronize_srcu(&kvm->srcu) ensured that kvm_gmem_get_pfn()
> @@ -659,18 +667,18 @@ static struct folio *__kvm_gmem_get_pfn(struct file *file,
>  					pgoff_t index, kvm_pfn_t *pfn,
>  					bool *is_prepared, int *max_order)
>  {
> -	struct file *gmem_file = READ_ONCE(slot->gmem.file);
> -	struct kvm_gmem *gmem = file->private_data;
> +	struct file *slot_file = READ_ONCE(slot->gmem.file);
> +	struct gmem_file *f = file->private_data;
			^^^
>  	struct folio *folio;
>  
> -	if (file != gmem_file) {
> -		WARN_ON_ONCE(gmem_file);
> +	if (file != slot_file) {
> +		WARN_ON_ONCE(slot_file);
>  		return ERR_PTR(-EFAULT);
>  	}
>  
> -	gmem = file->private_data;
> -	if (xa_load(&gmem->bindings, index) != slot) {
> -		WARN_ON_ONCE(xa_load(&gmem->bindings, index));
> +	f = file->private_data;

This redundant initialization can be dropped.

I sent a cleanup patch including this change a few weeks ago:

https://lore.kernel.org/kvm/20250902080307.153171-2-shivankg@amd.com

Could you please review it?

Everything else looks good to me!

Reviewed-by: Shivank Garg <shivankg@....com>

> +	if (xa_load(&f->bindings, index) != slot) {
> +		WARN_ON_ONCE(xa_load(&f->bindings, index));
>  		return ERR_PTR(-EIO);
>  	}
>  

Thanks,
Shivank

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