[RFC PATCH 15/39] KVM: guest_memfd: hugetlb: allocate and truncate from hugetlb

Ackerley Tng
2024-09-10T23:44:58Z

If HugeTLB is requested at guest_memfd creation time, HugeTLB pages
will be used to back guest_memfd.

Signed-off-by: Ackerley Tng <ackerleytng@google.com>
---
virt/kvm/guest_memfd.c | 252 ++++++++++++++++++++++++++++++++++++++---
1 file changed, 239 insertions(+), 13 deletions(-)

diff --git a/virt/kvm/guest_memfd.c b/virt/kvm/guest_memfd.c
index 31e1115273e1..2e6f12e2bac8 100644
--- a/virt/kvm/guest_memfd.c
+++ b/virt/kvm/guest_memfd.c
@@ -8,6 +8,8 @@
#include <linux/pseudo_fs.h>
#include <linux/pagemap.h>
#include <linux/anon_inodes.h>
+#include <linux/memcontrol.h>
+#include <linux/mempolicy.h>

#include "kvm_mm.h"

@@ -29,6 +31,13 @@ static struct kvm_gmem_hugetlb *kvm_gmem_hgmem(struct inode *inode)
return inode->i_mapping->i_private_data;
}

+static bool is_kvm_gmem_hugetlb(struct inode *inode)
+{
+ u64 flags = (u64)inode->i_private;
+
+ return flags & KVM_GUEST_MEMFD_HUGETLB;
+}
+
/**
* folio_file_pfn - like folio_file_page, but return a pfn.
* @folio: The folio which contains this index.
@@ -58,6 +67,9 @@ static int __kvm_gmem_prepare_folio(struct kvm *kvm, struct kvm_memory_slot *slo
return 0;
}

+/**
+ * Use the uptodate flag to indicate that the folio is prepared for KVM's usage.
+ */
static inline void kvm_gmem_mark_prepared(struct folio *folio)
{
folio_mark_uptodate(folio);
@@ -72,13 +84,18 @@ static inline void kvm_gmem_mark_prepared(struct folio *folio)
static int kvm_gmem_prepare_folio(struct kvm *kvm, struct kvm_memory_slot *slot,
gfn_t gfn, struct folio *folio)
{
- unsigned long nr_pages, i;
pgoff_t index;
int r;

- nr_pages = folio_nr_pages(folio);
- for (i = 0; i < nr_pages; i++)
- clear_highpage(folio_page(folio, i));
+ if (folio_test_hugetlb(folio)) {
+ folio_zero_user(folio, folio->index << PAGE_SHIFT);
+ } else {
+ unsigned long nr_pages, i;
+
+ nr_pages = folio_nr_pages(folio);
+ for (i = 0; i < nr_pages; i++)
+ clear_highpage(folio_page(folio, i));
+ }

/*
* Preparing huge folios should always be safe, since it should
@@ -103,6 +120,174 @@ static int kvm_gmem_prepare_folio(struct kvm *kvm, struct kvm_memory_slot *slot,
return r;
}

+static int kvm_gmem_get_mpol_node_nodemask(gfp_t gfp_mask,
+ struct mempolicy **mpol,
+ nodemask_t **nodemask)
+{
+ /*
+ * TODO: mempolicy would probably have to be stored on the inode, use
+ * task policy for now.
+ */
+ *mpol = get_task_policy(current);
+
+ /* TODO: ignore interleaving (set ilx to 0) for now. */
+ return policy_node_nodemask(*mpol, gfp_mask, 0, nodemask);
+}
+
+static struct folio *kvm_gmem_hugetlb_alloc_folio(struct hstate *h,
+ struct hugepage_subpool *spool)
+{
+ bool memcg_charge_was_prepared;
+ struct mem_cgroup *memcg;
+ struct mempolicy *mpol;
+ nodemask_t *nodemask;
+ struct folio *folio;
+ gfp_t gfp_mask;
+ int ret;
+ int nid;
+
+ gfp_mask = htlb_alloc_mask(h);
+
+ memcg = get_mem_cgroup_from_current();
+ ret = mem_cgroup_hugetlb_try_charge(memcg,
+ gfp_mask | __GFP_RETRY_MAYFAIL,
+ pages_per_huge_page(h));
+ if (ret == -ENOMEM)
+ goto err;
+
+ memcg_charge_was_prepared = ret != -EOPNOTSUPP;
+
+ /* Pages are only to be taken from guest_memfd subpool and nowhere else. */
+ if (hugepage_subpool_get_pages(spool, 1))
+ goto err_cancel_charge;
+
+ nid = kvm_gmem_get_mpol_node_nodemask(htlb_alloc_mask(h), &mpol,
+ &nodemask);
+ /*
+ * charge_cgroup_reservation is false because we didn't make any cgroup
+ * reservations when creating the guest_memfd subpool.
+ *
+ * use_hstate_resv is true because we reserved from global hstate when
+ * creating the guest_memfd subpool.
+ */
+ folio = hugetlb_alloc_folio(h, mpol, nid, nodemask, false, true);
+ mpol_cond_put(mpol);
+
+ if (!folio)
+ goto err_put_pages;
+
+ hugetlb_set_folio_subpool(folio, spool);
+
+ if (memcg_charge_was_prepared)
+ mem_cgroup_commit_charge(folio, memcg);
+
+out:
+ mem_cgroup_put(memcg);
+
+ return folio;
+
+err_put_pages:
+ hugepage_subpool_put_pages(spool, 1);
+
+err_cancel_charge:
+ if (memcg_charge_was_prepared)
+ mem_cgroup_cancel_charge(memcg, pages_per_huge_page(h));
+
+err:
+ folio = ERR_PTR(-ENOMEM);
+ goto out;
+}
+
+static int kvm_gmem_hugetlb_filemap_add_folio(struct address_space *mapping,
+ struct folio *folio, pgoff_t index,
+ gfp_t gfp)
+{
+ int ret;
+
+ __folio_set_locked(folio);
+ ret = __filemap_add_folio(mapping, folio, index, gfp, NULL);
+ if (unlikely(ret)) {
+ __folio_clear_locked(folio);
+ return ret;
+ }
+
+ /*
+ * In hugetlb_add_to_page_cache(), there is a call to
+ * folio_clear_hugetlb_restore_reserve(). This is handled when the pages
+ * are removed from the page cache in unmap_hugepage_range() ->
+ * __unmap_hugepage_range() by conditionally calling
+ * folio_set_hugetlb_restore_reserve(). In kvm_gmem_hugetlb's usage of
+ * hugetlb, there are no VMAs involved, and pages are never taken from
+ * the surplus, so when pages are freed, the hstate reserve must be
+ * restored. Hence, this function makes no call to
+ * folio_clear_hugetlb_restore_reserve().
+ */
+
+ /* mark folio dirty so that it will not be removed from cache/inode */
+ folio_mark_dirty(folio);
+
+ return 0;
+}
+
+static struct folio *kvm_gmem_hugetlb_alloc_and_cache_folio(struct inode *inode,
+ pgoff_t index)
+{
+ struct kvm_gmem_hugetlb *hgmem;
+ struct folio *folio;
+ int ret;
+
+ hgmem = kvm_gmem_hgmem(inode);
+ folio = kvm_gmem_hugetlb_alloc_folio(hgmem->h, hgmem->spool);
+ if (IS_ERR(folio))
+ return folio;
+
+ /* TODO: Fix index here to be aligned to huge page size. */
+ ret = kvm_gmem_hugetlb_filemap_add_folio(
+ inode->i_mapping, folio, index, htlb_alloc_mask(hgmem->h));
+ if (ret) {
+ folio_put(folio);
+ return ERR_PTR(ret);
+ }
+
+ spin_lock(&inode->i_lock);
+ inode->i_blocks += blocks_per_huge_page(hgmem->h);
+ spin_unlock(&inode->i_lock);
+
+ return folio;
+}
+
+static struct folio *kvm_gmem_get_hugetlb_folio(struct inode *inode,
+ pgoff_t index)
+{
+ struct address_space *mapping;
+ struct folio *folio;
+ struct hstate *h;
+ pgoff_t hindex;
+ u32 hash;
+
+ h = kvm_gmem_hgmem(inode)->h;
+ hindex = index >> huge_page_order(h);
+ mapping = inode->i_mapping;
+
+ /* To lock, we calculate the hash using the hindex and not index. */
+ hash = hugetlb_fault_mutex_hash(mapping, hindex);
+ mutex_lock(&hugetlb_fault_mutex_table[hash]);
+
+ /*
+ * The filemap is indexed with index and not hindex. Taking lock on
+ * folio to align with kvm_gmem_get_regular_folio()
+ */
+ folio = filemap_lock_folio(mapping, index);
+ if (!IS_ERR(folio))
+ goto out;
+
+ folio = kvm_gmem_hugetlb_alloc_and_cache_folio(inode, index);
+out:
+ mutex_unlock(&hugetlb_fault_mutex_table[hash]);
+
+ return folio;
+}
+
/*
* Returns a locked folio on success. The caller is responsible for
* setting the up-to-date flag before the memory is mapped into the guest.
@@ -114,8 +299,10 @@ static int kvm_gmem_prepare_folio(struct kvm *kvm, struct kvm_memory_slot *slot,
*/
static struct folio *kvm_gmem_get_folio(struct inode *inode, pgoff_t index)
{
- /* TODO: Support huge pages. */
- return filemap_grab_folio(inode->i_mapping, index);
+ if (is_kvm_gmem_hugetlb(inode))
+ return kvm_gmem_get_hugetlb_folio(inode, index);
+ else
+ return filemap_grab_folio(inode->i_mapping, index);
}

static void kvm_gmem_invalidate_begin(struct kvm_gmem *gmem, pgoff_t start,
@@ -240,6 +427,35 @@ static void kvm_gmem_hugetlb_truncate_folios_range(struct inode *inode,
spin_unlock(&inode->i_lock);
}

+static void kvm_gmem_hugetlb_truncate_range(struct inode *inode, loff_t lstart,
+ loff_t lend)
+{
+ loff_t full_hpage_start;
+ loff_t full_hpage_end;
+ unsigned long hsize;
+ struct hstate *h;
+
+ h = kvm_gmem_hgmem(inode)->h;
+ hsize = huge_page_size(h);
+
+ full_hpage_start = round_up(lstart, hsize);
+ full_hpage_end = round_down(lend, hsize);
+
+ if (lstart < full_hpage_start) {
+ hugetlb_zero_partial_page(h, inode->i_mapping, lstart,
+ full_hpage_start);
+ }
+
+ if (full_hpage_end > full_hpage_start) {
+ kvm_gmem_hugetlb_truncate_folios_range(inode, full_hpage_start,
+ full_hpage_end);
+ }
+
+ if (lend > full_hpage_end) {
+ hugetlb_zero_partial_page(h, inode->i_mapping, full_hpage_end,
+ lend);
+ }
+}

static long kvm_gmem_punch_hole(struct inode *inode, loff_t offset, loff_t len)
{
@@ -257,7 +473,12 @@ static long kvm_gmem_punch_hole(struct inode *inode, loff_t offset, loff_t len)
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);
+ if (is_kvm_gmem_hugetlb(inode)) {
+ kvm_gmem_hugetlb_truncate_range(inode, offset, offset + len);
+ } else {
+ 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);
@@ -279,8 +500,15 @@ static long kvm_gmem_allocate(struct inode *inode, loff_t offset, loff_t len)

filemap_invalidate_lock_shared(mapping);

- start = offset >> PAGE_SHIFT;
- end = (offset + len) >> PAGE_SHIFT;
+ if (is_kvm_gmem_hugetlb(inode)) {
+ unsigned long hsize = huge_page_size(kvm_gmem_hgmem(inode)->h);
+
+ start = round_down(offset, hsize) >> PAGE_SHIFT;
+ end = round_down(offset + len, hsize) >> PAGE_SHIFT;
+ } else {
+ start = offset >> PAGE_SHIFT;
+ end = (offset + len) >> PAGE_SHIFT;
+ }

r = 0;
for (index = start; index < end; ) {
@@ -408,9 +636,7 @@ static void kvm_gmem_hugetlb_teardown(struct inode *inode)

static void kvm_gmem_evict_inode(struct inode *inode)
{
- u64 flags = (u64)inode->i_private;
-
- if (flags & KVM_GUEST_MEMFD_HUGETLB)
+ if (is_kvm_gmem_hugetlb(inode))
kvm_gmem_hugetlb_teardown(inode);
else
truncate_inode_pages_final(inode->i_mapping);
@@ -827,7 +1053,7 @@ __kvm_gmem_get_pfn(struct file *file, struct kvm_memory_slot *slot,

*pfn = folio_file_pfn(folio, index);
if (max_order)
- *max_order = 0;
+ *max_order = folio_order(folio);

*is_prepared = folio_test_uptodate(folio);
return folio;
--
2.46.0.598.g6f2099f65c-goog