From: "Madhavan T. Venkataraman" <madvenka@xxxxxxxxxxxxxxxxxxx>
Introduce the "Persistent-Across-Kexec memory (prmem)" feature that allows
user and kernel data to be persisted across kexecs.
The first step is to set aside some memory for storing persistent data.
Introduce a new kernel command line parameter for this:
prmem=size[KMG]
Allocate this memory from memblocks during boot. Make sure that the
allocation is done late enough so it does not interfere with any fixed
range allocations.
Define a "prmem_region" structure to store the range that is allocated. The
region structure will be used to manage the memory.
Define a "prmem" structure for storing persistence metadata.
Allocate a metadata page to contain the metadata structure. Initialize the
metadata. Add the initial region to a region list in the metadata.
Signed-off-by: Madhavan T. Venkataraman <madvenka@xxxxxxxxxxxxxxxxxxx>
---
arch/x86/kernel/setup.c | 2 +
include/linux/prmem.h | 76 ++++++++++++++++++++++++++++++++++++
kernel/Makefile | 1 +
kernel/prmem/Makefile | 3 ++
kernel/prmem/prmem_init.c | 27 +++++++++++++
kernel/prmem/prmem_parse.c | 33 ++++++++++++++++
kernel/prmem/prmem_region.c | 21 ++++++++++
kernel/prmem/prmem_reserve.c | 56 ++++++++++++++++++++++++++
mm/mm_init.c | 2 +
9 files changed, 221 insertions(+)
create mode 100644 include/linux/prmem.h
create mode 100644 kernel/prmem/Makefile
create mode 100644 kernel/prmem/prmem_init.c
create mode 100644 kernel/prmem/prmem_parse.c
create mode 100644 kernel/prmem/prmem_region.c
create mode 100644 kernel/prmem/prmem_reserve.c
diff --git a/arch/x86/kernel/setup.c b/arch/x86/kernel/setup.c
index fd975a4a5200..f2b13b3d3ead 100644
--- a/arch/x86/kernel/setup.c
+++ b/arch/x86/kernel/setup.c
@@ -25,6 +25,7 @@
#include <linux/static_call.h>
#include <linux/swiotlb.h>
#include <linux/random.h>
+#include <linux/prmem.h>
#include <uapi/linux/mount.h>
@@ -1231,6 +1232,7 @@ void __init setup_arch(char **cmdline_p)
* won't consume hotpluggable memory.
*/
reserve_crashkernel();
+ prmem_reserve();
memblock_find_dma_reserve();
diff --git a/include/linux/prmem.h b/include/linux/prmem.h
new file mode 100644
index 000000000000..7f22016c4ad2
--- /dev/null
+++ b/include/linux/prmem.h
@@ -0,0 +1,76 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Persistent-Across-Kexec memory (prmem) - Definitions.
+ *
+ * Copyright (C) 2023 Microsoft Corporation
+ * Author: Madhavan T. Venkataraman (madvenka@xxxxxxxxxxxxxxxxxxx)
+ */
+#ifndef _LINUX_PRMEM_H
+#define _LINUX_PRMEM_H
+/*
+ * The prmem feature can be used to persist kernel and user data across kexec
+ * reboots in memory for various uses. E.g.,
+ *
+ * - Saving cached data. E.g., database caches.
+ * - Saving state. E.g., KVM guest states.
+ * - Saving historical information since the last cold boot such as
+ * events, logs and journals.
+ * - Saving measurements for integrity checks on the next boot.
+ * - Saving driver data.
+ * - Saving IOMMU mappings.
+ * - Saving MMIO config information.
+ *
+ * This is useful on systems where there is no non-volatile storage or
+ * non-volatile storage is too slow.
+ */
+#include <linux/types.h>
+#include <linux/init.h>
+#include <linux/kernel.h>
+#include <linux/memblock.h>
+#include <linux/printk.h>
+
+#include <asm-generic/errno.h>
+#include <asm/page.h>
+#include <asm/setup.h>
+/*
+ * A prmem region supplies the memory for storing persistent data.
+ *
+ * node List node.
+ * pa Physical address of the region.
+ * size Size of the region in bytes.
+ */
+struct prmem_region {
+ struct list_head node;
+ unsigned long pa;
+ size_t size;
+};
+
+/*
+ * PRMEM metadata.
+ *
+ * metadata Physical address of the metadata page.
+ * size Size of initial memory allocated to prmem.
+ *
+ * regions List of memory regions.
+ */
+struct prmem {
+ unsigned long metadata;
+ size_t size;
+
+ /* Persistent Regions. */
+ struct list_head regions;
+};
+
+extern struct prmem *prmem;
+extern unsigned long prmem_metadata;
+extern unsigned long prmem_pa;
+extern size_t prmem_size;
+
+/* Kernel API. */
+void prmem_reserve(void);
+void prmem_init(void);
+
+/* Internal functions. */
+struct prmem_region *prmem_add_region(unsigned long pa, size_t size);
+
+#endif /* _LINUX_PRMEM_H */
diff --git a/kernel/Makefile b/kernel/Makefile
index 3947122d618b..43b485b0467a 100644
--- a/kernel/Makefile
+++ b/kernel/Makefile
@@ -50,6 +50,7 @@ obj-y += rcu/
obj-y += livepatch/
obj-y += dma/
obj-y += entry/
+obj-y += prmem/
obj-$(CONFIG_MODULES) += module/
obj-$(CONFIG_KCMP) += kcmp.o
diff --git a/kernel/prmem/Makefile b/kernel/prmem/Makefile
new file mode 100644
index 000000000000..11a53d49312a
--- /dev/null
+++ b/kernel/prmem/Makefile
@@ -0,0 +1,3 @@
+# SPDX-License-Identifier: GPL-2.0
+
+obj-y += prmem_parse.o prmem_reserve.o prmem_init.o prmem_region.o
diff --git a/kernel/prmem/prmem_init.c b/kernel/prmem/prmem_init.c
new file mode 100644
index 000000000000..97b550252028
--- /dev/null
+++ b/kernel/prmem/prmem_init.c
@@ -0,0 +1,27 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Persistent-Across-Kexec memory (prmem) - Initialization.
+ *
+ * Copyright (C) 2023 Microsoft Corporation
+ * Author: Madhavan T. Venkataraman (madvenka@xxxxxxxxxxxxxxxxxxx)
+ */
+#include <linux/prmem.h>
+
+bool prmem_inited;
+
+void __init prmem_init(void)
+{
+ if (!prmem)
+ return;
+
+ if (!prmem->metadata) {
+ /* Cold boot. */
+ prmem->metadata = prmem_metadata;
+ prmem->size = prmem_size;
+ INIT_LIST_HEAD(&prmem->regions);
+
+ if (!prmem_add_region(prmem_pa, prmem_size))
+ return;
+ }
+ prmem_inited = true;
+}
diff --git a/kernel/prmem/prmem_parse.c b/kernel/prmem/prmem_parse.c
new file mode 100644
index 000000000000..191655b53545
--- /dev/null
+++ b/kernel/prmem/prmem_parse.c
@@ -0,0 +1,33 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Persistent-Across-Kexec memory (prmem) - Process prmem cmdline parameter.
+ *
+ * Copyright (C) 2023 Microsoft Corporation
+ * Author: Madhavan T. Venkataraman (madvenka@xxxxxxxxxxxxxxxxxxx)
+ */
+#include <linux/prmem.h>
+
+/*
+ * Syntax: prmem=size[KMG]
+ *
+ * Specifies the size of the initial memory to be allocated to prmem.
+ */
+static int __init prmem_size_parse(char *cmdline)
+{
+ char *tmp, *cur = cmdline;
+ unsigned long size;
+
+ if (!cur)
+ return -EINVAL;
+
+ /* Get initial size. */
+ size = memparse(cur, &tmp);
+ if (cur == tmp || !size || size & (PAGE_SIZE - 1)) {
+ pr_warn("%s: Incorrect size %lx\n", __func__, size);
+ return -EINVAL;
+ }
+
+ prmem_size = size;
+ return 0;
+}
+early_param("prmem", prmem_size_parse);
diff --git a/kernel/prmem/prmem_region.c b/kernel/prmem/prmem_region.c
new file mode 100644
index 000000000000..8254dafcee13
--- /dev/null
+++ b/kernel/prmem/prmem_region.c
@@ -0,0 +1,21 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Persistent-Across-Kexec memory (prmem) - Regions.
+ *
+ * Copyright (C) 2023 Microsoft Corporation
+ * Author: Madhavan T. Venkataraman (madvenka@xxxxxxxxxxxxxxxxxxx)
+ */
+#include <linux/prmem.h>
+
+struct prmem_region *prmem_add_region(unsigned long pa, size_t size)
+{
+ struct prmem_region *region;
+
+ /* Allocate region structure from the base of the region itself. */
+ region = __va(pa);
+ region->pa = pa;
+ region->size = size;
+
+ list_add_tail(®ion->node, &prmem->regions);
+ return region;
+}
diff --git a/kernel/prmem/prmem_reserve.c b/kernel/prmem/prmem_reserve.c
new file mode 100644
index 000000000000..e20e31a61d12
--- /dev/null
+++ b/kernel/prmem/prmem_reserve.c
@@ -0,0 +1,56 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Persistent-Across-Kexec memory (prmem) - Reserve memory.
+ *
+ * Copyright (C) 2023 Microsoft Corporation
+ * Author: Madhavan T. Venkataraman (madvenka@xxxxxxxxxxxxxxxxxxx)
+ */
+#include <linux/prmem.h>
+
+struct prmem *prmem;
+unsigned long prmem_metadata;
+unsigned long prmem_pa;
+unsigned long prmem_size;
+
+void __init prmem_reserve(void)
+{
+ BUILD_BUG_ON(sizeof(*prmem) > PAGE_SIZE);
+
+ if (!prmem_size)
+ return;
+
+ /*
+ * prmem uses direct map addresses. If PAGE_OFFSET is randomized,
+ * these addresses will change across kexecs. Persistence cannot
+ * be supported.
+ */
+ if (kaslr_memory_enabled()) {
+ pr_warn("%s: Cannot support persistence because of KASLR.\n",
+ __func__);
+ return;
+ }
+
+ /* Allocate a metadata page. */
+ prmem_metadata = memblock_phys_alloc(PAGE_SIZE, PAGE_SIZE);
+ if (!prmem_metadata) {
+ pr_warn("%s: Could not allocate metadata at %lx\n", __func__,
+ prmem_metadata);
+ return;
+ }
+
+ /* Allocate initial memory. */
+ prmem_pa = memblock_phys_alloc(prmem_size, PAGE_SIZE);
+ if (!prmem_pa) {
+ pr_warn("%s: Could not allocate initial memory\n", __func__);
+ goto free_metadata;
+ }
+
+ /* Clear metadata. */
+ prmem = __va(prmem_metadata);
+ memset(prmem, 0, sizeof(*prmem));
+ return;
+
+free_metadata:
+ memblock_phys_free(prmem_metadata, PAGE_SIZE);
+ prmem = NULL;
+}
diff --git a/mm/mm_init.c b/mm/mm_init.c
index a1963c3322af..f12757829281 100644
--- a/mm/mm_init.c
+++ b/mm/mm_init.c
@@ -24,6 +24,7 @@
#include <linux/page_ext.h>
#include <linux/pti.h>
#include <linux/pgtable.h>
+#include <linux/prmem.h>
#include <linux/swap.h>
#include <linux/cma.h>
#include "internal.h"
@@ -2804,4 +2805,5 @@ void __init mm_core_init(void)
pti_init();
kmsan_init_runtime();
mm_cache_init();
+ prmem_init();
}
--
2.25.1
