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Message-ID: <8f8b6d6f44cdc6b27db11e1e867dc92efca6d177.1747264138.git.ackerleytng@google.com>
Date: Wed, 14 May 2025 16:42:07 -0700
From: Ackerley Tng <ackerleytng@...gle.com>
To: kvm@...r.kernel.org, linux-mm@...ck.org, linux-kernel@...r.kernel.org,
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Subject: [RFC PATCH v2 28/51] mm: Introduce guestmem_hugetlb to support
folio_put() handling of guestmem pages
The PGTY_guestmem_hugetlb is introduced so folios can be marked for
further cleanup by guestmem_hugetlb.
guestmem_hugetlb folios can have positive mapcounts, which will
conflict with the installation of a page type. Hence,
PGTY_guestmem_hugetlb will only be installed when a folio is
truncated, after the folio has been unmapped and has a mapcount of 0.
Signed-off-by: Fuad Tabba <tabba@...gle.com>
Acked-by: Vlastimil Babka <vbabka@...e.cz>
Acked-by: David Hildenbrand <david@...hat.com>
Signed-off-by: Ackerley Tng <ackerleytng@...gle.com>
Change-Id: I635f8929e06f73d7899737bd47090b7cbc7222dc
---
include/linux/page-flags.h | 17 +++++++++++++++++
mm/Kconfig | 10 ++++++++++
mm/Makefile | 1 +
mm/debug.c | 1 +
mm/guestmem_hugetlb.c | 14 ++++++++++++++
mm/guestmem_hugetlb.h | 9 +++++++++
mm/swap.c | 9 +++++++++
7 files changed, 61 insertions(+)
create mode 100644 mm/guestmem_hugetlb.c
create mode 100644 mm/guestmem_hugetlb.h
diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
index 9dd60fb8c33f..543f6481ca60 100644
--- a/include/linux/page-flags.h
+++ b/include/linux/page-flags.h
@@ -965,6 +965,7 @@ enum pagetype {
PGTY_zsmalloc = 0xf6,
PGTY_unaccepted = 0xf7,
PGTY_large_kmalloc = 0xf8,
+ PGTY_guestmem_hugetlb = 0xf9,
PGTY_mapcount_underflow = 0xff
};
@@ -1114,6 +1115,22 @@ FOLIO_TYPE_OPS(hugetlb, hugetlb)
FOLIO_TEST_FLAG_FALSE(hugetlb)
#endif
+/*
+ * PGTY_guestmem_hugetlb, for now, is used to mark a folio as requiring further
+ * cleanup by the guestmem_hugetlb allocator. This page type is installed only
+ * at truncation time, by guest_memfd, if further cleanup is required. It is
+ * safe to install this page type at truncation time because by then mapcount
+ * would be 0.
+ *
+ * The plan is to always set this page type for any folios allocated by
+ * guestmem_hugetlb once typed folios can be mapped to userspace cleanly.
+ */
+#ifdef CONFIG_GUESTMEM_HUGETLB
+FOLIO_TYPE_OPS(guestmem_hugetlb, guestmem_hugetlb)
+#else
+FOLIO_TEST_FLAG_FALSE(guestmem_hugetlb)
+#endif
+
PAGE_TYPE_OPS(Zsmalloc, zsmalloc, zsmalloc)
/*
diff --git a/mm/Kconfig b/mm/Kconfig
index e113f713b493..131adc49f58d 100644
--- a/mm/Kconfig
+++ b/mm/Kconfig
@@ -1216,6 +1216,16 @@ config SECRETMEM
memory areas visible only in the context of the owning process and
not mapped to other processes and other kernel page tables.
+config GUESTMEM_HUGETLB
+ bool "Enable guestmem_hugetlb allocator for guest_memfd"
+ depends on HUGETLBFS
+ help
+ Enable this to make HugeTLB folios available to guest_memfd
+ (KVM virtualization) as backing memory.
+
+ This feature wraps HugeTLB as a custom allocator that
+ guest_memfd can use.
+
config ANON_VMA_NAME
bool "Anonymous VMA name support"
depends on PROC_FS && ADVISE_SYSCALLS && MMU
diff --git a/mm/Makefile b/mm/Makefile
index e7f6bbf8ae5f..c91c8e8fef71 100644
--- a/mm/Makefile
+++ b/mm/Makefile
@@ -127,6 +127,7 @@ obj-$(CONFIG_PAGE_EXTENSION) += page_ext.o
obj-$(CONFIG_PAGE_TABLE_CHECK) += page_table_check.o
obj-$(CONFIG_CMA_DEBUGFS) += cma_debug.o
obj-$(CONFIG_SECRETMEM) += secretmem.o
+obj-$(CONFIG_GUESTMEM_HUGETLB) += guestmem_hugetlb.o
obj-$(CONFIG_CMA_SYSFS) += cma_sysfs.o
obj-$(CONFIG_USERFAULTFD) += userfaultfd.o
obj-$(CONFIG_IDLE_PAGE_TRACKING) += page_idle.o
diff --git a/mm/debug.c b/mm/debug.c
index db83e381a8ae..439ab128772d 100644
--- a/mm/debug.c
+++ b/mm/debug.c
@@ -56,6 +56,7 @@ static const char *page_type_names[] = {
DEF_PAGETYPE_NAME(table),
DEF_PAGETYPE_NAME(buddy),
DEF_PAGETYPE_NAME(unaccepted),
+ DEF_PAGETYPE_NAME(guestmem_hugetlb),
};
static const char *page_type_name(unsigned int page_type)
diff --git a/mm/guestmem_hugetlb.c b/mm/guestmem_hugetlb.c
new file mode 100644
index 000000000000..51a724ebcc50
--- /dev/null
+++ b/mm/guestmem_hugetlb.c
@@ -0,0 +1,14 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * guestmem_hugetlb is an allocator for guest_memfd. guest_memfd wraps HugeTLB
+ * as an allocator for guest_memfd.
+ */
+
+#include <linux/mm_types.h>
+
+#include "guestmem_hugetlb.h"
+
+void guestmem_hugetlb_handle_folio_put(struct folio *folio)
+{
+ WARN_ONCE(1, "A placeholder that shouldn't trigger. Work in progress.");
+}
diff --git a/mm/guestmem_hugetlb.h b/mm/guestmem_hugetlb.h
new file mode 100644
index 000000000000..5c9452b77252
--- /dev/null
+++ b/mm/guestmem_hugetlb.h
@@ -0,0 +1,9 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _LINUX_MM_GUESTMEM_HUGETLB_H
+#define _LINUX_MM_GUESTMEM_HUGETLB_H
+
+#include <linux/mm_types.h>
+
+void guestmem_hugetlb_handle_folio_put(struct folio *folio);
+
+#endif
diff --git a/mm/swap.c b/mm/swap.c
index d0a5971787c4..2747230ced89 100644
--- a/mm/swap.c
+++ b/mm/swap.c
@@ -40,6 +40,10 @@
#include "internal.h"
+#ifdef CONFIG_GUESTMEM_HUGETLB
+#include "guestmem_hugetlb.h"
+#endif
+
#define CREATE_TRACE_POINTS
#include <trace/events/pagemap.h>
@@ -101,6 +105,11 @@ static void free_typed_folio(struct folio *folio)
case PGTY_hugetlb:
free_huge_folio(folio);
return;
+#endif
+#ifdef CONFIG_GUESTMEM_HUGETLB
+ case PGTY_guestmem_hugetlb:
+ guestmem_hugetlb_handle_folio_put(folio);
+ return;
#endif
default:
WARN_ON_ONCE(1);
--
2.49.0.1045.g170613ef41-goog
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