On Fri, Apr 26, 2024, Paolo Bonzini wrote:
> On Thu, Apr 25, 2024 at 6:00 PM Sean Christopherson <seanjc@xxxxxxxxxx> wrote:
> >
> > On Thu, Apr 25, 2024, Paolo Bonzini wrote:
> > > On Thu, Apr 25, 2024 at 3:12 AM Isaku Yamahata <isaku.yamahata@xxxxxxxxx> wrote:
> > > > > > get_user_pages_fast(source addr)
> > > > > > read_lock(mmu_lock)
> > > > > > kvm_tdp_mmu_get_walk_private_pfn(vcpu, gpa, &pfn);
> > > > > > if the page table doesn't map gpa, error.
> > > > > > TDH.MEM.PAGE.ADD()
> > > > > > TDH.MR.EXTEND()
> > > > > > read_unlock(mmu_lock)
> > > > > > put_page()
> > > > >
> > > > > Hmm, KVM doesn't _need_ to use invalidate_lock to protect against guest_memfd
> > > > > invalidation, but I also don't see why it would cause problems.
> > >
> > > The invalidate_lock is only needed to operate on the guest_memfd, but
> > > it's a rwsem so there are no risks of lock inversion.
> > >
> > > > > I.e. why not
> > > > > take mmu_lock() in TDX's post_populate() implementation?
> > > >
> > > > We can take the lock. Because we have already populated the GFN of guest_memfd,
> > > > we need to make kvm_gmem_populate() not pass FGP_CREAT_ONLY. Otherwise we'll
> > > > get -EEXIST.
> > >
> > > I don't understand why TDH.MEM.PAGE.ADD() cannot be called from the
> > > post-populate hook. Can the code for TDH.MEM.PAGE.ADD be shared
> > > between the memory initialization ioctl and the page fault hook in
> > > kvm_x86_ops?
> >
> > Ah, because TDX is required to pre-fault the memory to establish the S-EPT walk,
> > and pre-faulting means guest_memfd()
> >
> > Requiring that guest_memfd not have a page when initializing the guest image
> > seems wrong, i.e. I don't think we want FGP_CREAT_ONLY. And not just because I
> > am a fan of pre-faulting, I think the semantics are bad.
>
> Ok, fair enough. I wanted to do the once-only test in common code but since
> SEV code checks for the RMP I can remove that. One less headache.
I definitely don't object to having a check in common code, and I'd be in favor
of removing the RMP checks if possible, but tracking needs to be something more
explicit in guest_memfd.
*sigh*
I even left behind a TODO for this exact thing, and y'all didn't even wave at it
as you flew by :-)
/*
* 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);
}
if (prepare) {
int r = kvm_gmem_prepare_folio(inode, index, folio);
if (r < 0) {
folio_unlock(folio);
folio_put(folio);
return ERR_PTR(r);
}
}
Compile tested only (and not even fully as I didn't bother defining
CONFIG_HAVE_KVM_GMEM_INITIALIZE), but I think this is the basic gist.
8< --------------------------------
// 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/anon_inodes.h>
#include "kvm_mm.h"
struct kvm_gmem {
struct kvm *kvm;
struct xarray bindings;
struct list_head entry;
};
static int kvm_gmem_initialize_folio(struct kvm *kvm, struct folio *folio,
pgoff_t index, void __user *src,
void *opaque)
{
#ifdef CONFIG_HAVE_KVM_GMEM_INITIALIZE
return kvm_arch_gmem_initialize(kvm, folio, index, src, opaque);
#else
unsigned long nr_pages = folio_nr_pages(folio);
unsigned long i;
if (WARN_ON_ONCE(src))
return -EIO;
for (i = 0; i < nr_pages; i++)
clear_highpage(folio_file_page(folio, index + i));
#endif
return 0;
}
static pgoff_t kvm_gmem_get_index(struct kvm_memory_slot *slot, gfn_t gfn)
{
return gfn - slot->base_gfn + slot->gmem.pgoff;
}
static inline struct file *kvm_gmem_get_file(struct kvm_memory_slot *slot)
{
/*
* Do not return slot->gmem.file if it has already been closed;
* there might be some time between the last fput() and when
* kvm_gmem_release() clears slot->gmem.file, and you do not
* want to spin in the meanwhile.
*/
return get_file_active(&slot->gmem.file);
}
static struct folio *__kvm_gmem_get_folio(struct inode *inode, pgoff_t index)
{
fgf_t fgp_flags = FGP_LOCK | FGP_ACCESSED | FGP_CREAT;
struct folio *folio;
/*
* The caller is responsible for managing the up-to-date flag (or not),
* as the memory doesn't need to be initialized until it's actually
* mapped into the guest. Waiting to initialize memory is necessary
* for VM types where the memory can be initialized exactly once.
*
* Ignore accessed, referenced, and dirty flags. The memory is
* unevictable and there is no storage to write back to.
*
* TODO: Support huge pages.
*/
folio = __filemap_get_folio(inode->i_mapping, index, fgp_flags,
mapping_gfp_mask(inode->i_mapping));
if (folio_test_hwpoison(folio)) {
folio_unlock(folio);
return ERR_PTR(-EHWPOISON);
}
return folio;
}
static struct folio *kvm_gmem_get_folio(struct file *file,
struct kvm_memory_slot *slot,
gfn_t gfn)
{
pgoff_t index = kvm_gmem_get_index(slot, gfn);
struct kvm_gmem *gmem = file->private_data;
struct inode *inode;
if (file != slot->gmem.file) {
WARN_ON_ONCE(slot->gmem.file);
return ERR_PTR(-EFAULT);
}
gmem = file->private_data;
if (xa_load(&gmem->bindings, index) != slot) {
WARN_ON_ONCE(xa_load(&gmem->bindings, index));
return ERR_PTR(-EIO);
}
inode = file_inode(file);
/*
* The caller is responsible for managing the up-to-date flag (or not),
* as the memory doesn't need to be initialized until it's actually
* mapped into the guest. Waiting to initialize memory is necessary
* for VM types where the memory can be initialized exactly once.
*
* Ignore accessed, referenced, and dirty flags. The memory is
* unevictable and there is no storage to write back to.
*
* TODO: Support huge pages.
*/
return __kvm_gmem_get_folio(inode, index);
}
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 = kvm_gmem_get_index(slot, gfn);
struct file *file = kvm_gmem_get_file(slot);
struct folio *folio;
struct page *page;
if (!file)
return -EFAULT;
folio = kvm_gmem_get_folio(file, slot, gfn);
if (IS_ERR(folio))
goto out;
if (!folio_test_uptodate(folio)) {
kvm_gmem_initialize_folio(kvm, folio, index, NULL, NULL);
folio_mark_uptodate(folio);
}
page = folio_file_page(folio, index);
*pfn = page_to_pfn(page);
if (max_order)
*max_order = 0;
out:
fput(file);
return IS_ERR(folio) ? PTR_ERR(folio) : 0;
}
EXPORT_SYMBOL_GPL(kvm_gmem_get_pfn);
long kvm_gmem_populate(struct kvm *kvm, gfn_t base_gfn, void __user *base_src,
long npages, void *opaque)
{
struct kvm_memory_slot *slot;
struct file *file;
int ret = 0, max_order;
long i;
lockdep_assert_held(&kvm->slots_lock);
if (npages < 0)
return -EINVAL;
slot = gfn_to_memslot(kvm, base_gfn);
if (!kvm_slot_can_be_private(slot))
return -EINVAL;
file = kvm_gmem_get_file(slot);
if (!file)
return -EFAULT;
filemap_invalidate_lock(file->f_mapping);
npages = min_t(ulong, slot->npages - (base_gfn - slot->base_gfn), npages);
for (i = 0; i < npages; i += (1 << max_order)) {
void __user *src = base_src + i * PAGE_SIZE;
gfn_t gfn = base_gfn + i;
pgoff_t index = kvm_gmem_get_index(slot, gfn);
struct folio *folio;
folio = kvm_gmem_get_folio(file, slot, gfn);
if (IS_ERR(folio)) {
ret = PTR_ERR(folio);
break;
}
if (folio_test_uptodate(folio)) {
folio_put(folio);
ret = -EEXIST;
break;
}
kvm_gmem_initialize_folio(kvm, folio, index, src, opaque);
folio_unlock(folio);
folio_put(folio);
}
filemap_invalidate_unlock(file->f_mapping);
fput(file);
return ret && !i ? ret : i;
}
EXPORT_SYMBOL_GPL(kvm_gmem_populate);
static void kvm_gmem_invalidate_begin(struct kvm_gmem *gmem, pgoff_t start,
pgoff_t end)
{
bool flush = false, found_memslot = false;
struct kvm_memory_slot *slot;
struct kvm *kvm = gmem->kvm;
unsigned long index;
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,
};
if (!found_memslot) {
found_memslot = true;
KVM_MMU_LOCK(kvm);
kvm_mmu_invalidate_begin(kvm);
}
flush |= kvm_mmu_unmap_gfn_range(kvm, &gfn_range);
}
if (flush)
kvm_flush_remote_tlbs(kvm);
if (found_memslot)
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;
if (xa_find(&gmem->bindings, &start, end - 1, XA_PRESENT)) {
KVM_MMU_LOCK(kvm);
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->i_private_list;
pgoff_t start = offset >> PAGE_SHIFT;
pgoff_t end = (offset + len) >> PAGE_SHIFT;
struct kvm_gmem *gmem;
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);
return 0;
}
static long kvm_gmem_punch_hole(struct inode *inode, loff_t offset, loff_t len)
{
int r;
/*
* Bindings must be stable across invalidation to ensure the start+end
* are balanced.
*/
filemap_invalidate_lock(inode->i_mapping);
r = __kvm_gmem_punch_hole(inode, offset, len);
filemap_invalidate_unlock(inode->i_mapping);
return r;
}
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 (IS_ERR(folio)) {
r = PTR_ERR(folio);
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;
/*
* 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);
filemap_invalidate_lock(inode->i_mapping);
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);
list_del(&gmem->entry);
filemap_invalidate_unlock(inode->i_mapping);
mutex_unlock(&kvm->slots_lock);
xa_destroy(&gmem->bindings);
kfree(gmem);
kvm_put_kvm(kvm);
return 0;
}
static struct file_operations kvm_gmem_fops = {
.open = generic_file_open,
.release = kvm_gmem_release,
.fallocate = kvm_gmem_fallocate,
};
void kvm_gmem_init(struct module *module)
{
kvm_gmem_fops.owner = module;
}
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_folio(struct address_space *mapping, struct folio *folio)
{
struct list_head *gmem_list = &mapping->i_private_list;
struct kvm_gmem *gmem;
pgoff_t start, end;
filemap_invalidate_lock_shared(mapping);
start = folio->index;
end = start + folio_nr_pages(folio);
list_for_each_entry(gmem, gmem_list, entry)
kvm_gmem_invalidate_begin(gmem, start, end);
/*
* Do not truncate the range, what action is taken in response to the
* error is userspace's decision (assuming the architecture supports
* gracefully handling memory errors). If/when the guest attempts to
* access a poisoned page, kvm_gmem_get_pfn() will return -EHWPOISON,
* at which point KVM can either terminate the VM or propagate the
* error to userspace.
*/
list_for_each_entry(gmem, gmem_list, entry)
kvm_gmem_invalidate_end(gmem, start, end);
filemap_invalidate_unlock_shared(mapping);
return MF_DELAYED;
}
#ifdef CONFIG_HAVE_KVM_GMEM_INVALIDATE
static void kvm_gmem_free_folio(struct folio *folio)
{
struct page *page = folio_page(folio, 0);
kvm_pfn_t pfn = page_to_pfn(page);
int order = folio_order(folio);
kvm_arch_gmem_invalidate(pfn, pfn + (1ul << order));
}
#endif
static const struct address_space_operations kvm_gmem_aops = {
.dirty_folio = noop_dirty_folio,
.migrate_folio = kvm_gmem_migrate_folio,
.error_remove_folio = kvm_gmem_error_folio,
#ifdef CONFIG_HAVE_KVM_GMEM_INVALIDATE
.free_folio = kvm_gmem_free_folio,
#endif
};
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;
generic_fillattr(idmap, request_mask, inode, stat);
return 0;
}
static int kvm_gmem_setattr(struct mnt_idmap *idmap, struct dentry *dentry,
struct iattr *attr)
{
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, u64 flags)
{
const char *anon_name = "[kvm-gmem]";
struct kvm_gmem *gmem;
struct inode *inode;
struct file *file;
int fd, err;
fd = get_unused_fd_flags(0);
if (fd < 0)
return fd;
gmem = kzalloc(sizeof(*gmem), GFP_KERNEL);
if (!gmem) {
err = -ENOMEM;
goto err_fd;
}
file = anon_inode_create_getfile(anon_name, &kvm_gmem_fops, gmem,
O_RDWR, NULL);
if (IS_ERR(file)) {
err = PTR_ERR(file);
goto err_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_op = &kvm_gmem_iops;
inode->i_mapping->a_ops = &kvm_gmem_aops;
inode->i_mapping->flags |= AS_INACCESSIBLE;
inode->i_mode |= S_IFREG;
inode->i_size = size;
mapping_set_gfp_mask(inode->i_mapping, GFP_HIGHUSER);
mapping_set_unmovable(inode->i_mapping);
/* Unmovable mappings are supposed to be marked unevictable as well. */
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);
fd_install(fd, file);
return fd;
err_gmem:
kfree(gmem);
err_fd:
put_unused_fd(fd);
return err;
}
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 (size <= 0 || !PAGE_ALIGNED(size))
return -EINVAL;
return __kvm_gmem_create(kvm, size, flags);
}
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;
struct kvm_gmem *gmem;
struct inode *inode;
struct file *file;
int r = -EINVAL;
BUILD_BUG_ON(sizeof(gfn_t) != sizeof(slot->gmem.pgoff));
file = fget(fd);
if (!file)
return -EBADF;
if (file->f_op != &kvm_gmem_fops)
goto err;
gmem = file->private_data;
if (gmem->kvm != kvm)
goto err;
inode = file_inode(file);
if (offset < 0 || !PAGE_ALIGNED(offset) ||
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.
*/
r = 0;
err:
fput(file);
return r;
}
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);
}
