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From:   Alexander Graf <graf@amazon.com>
To:     <linux-kernel@vger.kernel.org>
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        <devicetree@vger.kernel.org>,
        <linux-arm-kernel@lists.infradead.org>,
        <kexec@lists.infradead.org>, <linux-doc@vger.kernel.org>,
        <x86@kernel.org>, Eric Biederman <ebiederm@xmission.com>,
        "H. Peter Anvin" <hpa@zytor.com>,
        Andy Lutomirski <luto@kernel.org>,
        Peter Zijlstra <peterz@infradead.org>,
        "Rob Herring" <robh+dt@kernel.org>,
        Steven Rostedt <rostedt@goodmis.org>,
        "Andrew Morton" <akpm@linux-foundation.org>,
        Mark Rutland <mark.rutland@arm.com>,
        "Tom Lendacky" <thomas.lendacky@amd.com>,
        Ashish Kalra <ashish.kalra@amd.com>,
        James Gowans <jgowans@amazon.com>,
        Stanislav Kinsburskii <skinsburskii@linux.microsoft.com>,
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        <madvenka@linux.microsoft.com>,
        Anthony Yznaga <anthony.yznaga@oracle.com>,
        Usama Arif <usama.arif@bytedance.com>,
        David Woodhouse <dwmw@amazon.co.uk>,
        Benjamin Herrenschmidt <benh@kernel.crashing.org>
Subject: [PATCH 07/15] x86: Add KHO support
Date:   Wed, 13 Dec 2023 00:04:44 +0000
Message-ID: <20231213000452.88295-8-graf@amazon.com>
In-Reply-To: <20231213000452.88295-1-graf@amazon.com>
References: <20231213000452.88295-1-graf@amazon.com>
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We now have all bits in place to support KHO kexecs. This patch adds
awareness of KHO in the kexec file as well as boot path for x86 and
adds the respective kconfig option to the architecture so that it can
use KHO successfully.

In addition, it enlightens it decompression code with KHO so that its
KASLR location finder only considers memory regions that are not already
occupied by KHO memory.

Signed-off-by: Alexander Graf <graf@amazon.com>
---
 arch/x86/Kconfig                      | 12 ++++++
 arch/x86/boot/compressed/kaslr.c      | 55 +++++++++++++++++++++++++++
 arch/x86/include/uapi/asm/bootparam.h | 15 +++++++-
 arch/x86/kernel/e820.c                |  9 +++++
 arch/x86/kernel/kexec-bzimage64.c     | 39 +++++++++++++++++++
 arch/x86/kernel/setup.c               | 46 ++++++++++++++++++++++
 arch/x86/mm/init_32.c                 |  7 ++++
 arch/x86/mm/init_64.c                 |  7 ++++
 8 files changed, 189 insertions(+), 1 deletion(-)

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 3762f41bb092..849e6ddc5d94 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -2103,6 +2103,18 @@ config ARCH_SUPPORTS_CRASH_HOTPLUG
 config ARCH_HAS_GENERIC_CRASHKERNEL_RESERVATION
 	def_bool CRASH_CORE
 
+config KEXEC_KHO
+	bool "kexec handover"
+	depends on KEXEC
+	select MEMBLOCK_SCRATCH
+	select LIBFDT
+	select CMA
+	help
+	  Allow kexec to hand over state across kernels by generating and
+	  passing additional metadata to the target kernel. This is useful
+	  to keep data or state alive across the kexec. For this to work,
+	  both source and target kernels need to have this option enabled.
+
 config PHYSICAL_START
 	hex "Physical address where the kernel is loaded" if (EXPERT || CRASH_DUMP)
 	default "0x1000000"
diff --git a/arch/x86/boot/compressed/kaslr.c b/arch/x86/boot/compressed/kaslr.c
index dec961c6d16a..93ea292e4c18 100644
--- a/arch/x86/boot/compressed/kaslr.c
+++ b/arch/x86/boot/compressed/kaslr.c
@@ -29,6 +29,7 @@
 #include <linux/uts.h>
 #include <linux/utsname.h>
 #include <linux/ctype.h>
+#include <uapi/linux/kexec.h>
 #include <generated/utsversion.h>
 #include <generated/utsrelease.h>
 
@@ -472,6 +473,60 @@ static bool mem_avoid_overlap(struct mem_vector *img,
 			}
 		}
 
+#ifdef CONFIG_KEXEC_KHO
+		if (ptr->type == SETUP_KEXEC_KHO) {
+			struct kho_data *kho = (struct kho_data *)ptr->data;
+			struct kho_mem *mems = (void *)kho->mem_cache_addr;
+			int nr_mems = kho->mem_cache_size / sizeof(*mems);
+			int i;
+
+			/* Avoid the mem cache */
+			avoid = (struct mem_vector) {
+				.start = kho->mem_cache_addr,
+				.size = kho->mem_cache_size,
+			};
+
+			if (mem_overlaps(img, &avoid) && (avoid.start < earliest)) {
+				*overlap = avoid;
+				earliest = overlap->start;
+				is_overlapping = true;
+			}
+
+			/* And the KHO DT */
+			avoid = (struct mem_vector) {
+				.start = kho->dt_addr,
+				.size = kho->dt_size,
+			};
+
+			if (mem_overlaps(img, &avoid) && (avoid.start < earliest)) {
+				*overlap = avoid;
+				earliest = overlap->start;
+				is_overlapping = true;
+			}
+
+			/* As well as any other KHO memory reservations */
+			for (i = 0; i < nr_mems; i++) {
+				avoid = (struct mem_vector) {
+					.start = mems[i].addr,
+					.size = mems[i].len,
+				};
+
+				/*
+				 * This mem starts after our current break.
+				 * The array is sorted, so we're done.
+				 */
+				if (avoid.start >= earliest)
+					break;
+
+				if (mem_overlaps(img, &avoid)) {
+					*overlap = avoid;
+					earliest = overlap->start;
+					is_overlapping = true;
+				}
+			}
+		}
+#endif
+
 		ptr = (struct setup_data *)(unsigned long)ptr->next;
 	}
 
diff --git a/arch/x86/include/uapi/asm/bootparam.h b/arch/x86/include/uapi/asm/bootparam.h
index 01d19fc22346..013af38a9673 100644
--- a/arch/x86/include/uapi/asm/bootparam.h
+++ b/arch/x86/include/uapi/asm/bootparam.h
@@ -13,7 +13,8 @@
 #define SETUP_CC_BLOB			7
 #define SETUP_IMA			8
 #define SETUP_RNG_SEED			9
-#define SETUP_ENUM_MAX			SETUP_RNG_SEED
+#define SETUP_KEXEC_KHO		10
+#define SETUP_ENUM_MAX			SETUP_KEXEC_KHO
 
 #define SETUP_INDIRECT			(1<<31)
 #define SETUP_TYPE_MAX			(SETUP_ENUM_MAX | SETUP_INDIRECT)
@@ -181,6 +182,18 @@ struct ima_setup_data {
 	__u64 size;
 } __attribute__((packed));
 
+/*
+ * Locations of kexec handover metadata
+ */
+struct kho_data {
+	__u64 dt_addr;
+	__u64 dt_size;
+	__u64 scratch_addr;
+	__u64 scratch_size;
+	__u64 mem_cache_addr;
+	__u64 mem_cache_size;
+} __attribute__((packed));
+
 /* The so-called "zeropage" */
 struct boot_params {
 	struct screen_info screen_info;			/* 0x000 */
diff --git a/arch/x86/kernel/e820.c b/arch/x86/kernel/e820.c
index fb8cf953380d..c891b83f5b1c 100644
--- a/arch/x86/kernel/e820.c
+++ b/arch/x86/kernel/e820.c
@@ -1341,6 +1341,15 @@ void __init e820__memblock_setup(void)
 			continue;
 
 		memblock_add(entry->addr, entry->size);
+
+		/*
+		 * At this point with KHO we only allocate from scratch memory
+		 * and only from memory below ISA_END_ADDRESS. Make sure that
+		 * when we add memory for the eligible range, we add it as
+		 * scratch memory so that we can resize the memblocks array.
+		 */
+		if (is_kho_boot() && (end <= ISA_END_ADDRESS))
+			memblock_mark_scratch(entry->addr, end);
 	}
 
 	/* Throw away partial pages: */
diff --git a/arch/x86/kernel/kexec-bzimage64.c b/arch/x86/kernel/kexec-bzimage64.c
index a61c12c01270..0cb8d0650a02 100644
--- a/arch/x86/kernel/kexec-bzimage64.c
+++ b/arch/x86/kernel/kexec-bzimage64.c
@@ -15,6 +15,7 @@
 #include <linux/slab.h>
 #include <linux/kexec.h>
 #include <linux/kernel.h>
+#include <linux/libfdt.h>
 #include <linux/mm.h>
 #include <linux/efi.h>
 #include <linux/random.h>
@@ -233,6 +234,33 @@ setup_ima_state(const struct kimage *image, struct boot_params *params,
 #endif /* CONFIG_IMA_KEXEC */
 }
 
+static void setup_kho(const struct kimage *image, struct boot_params *params,
+		       unsigned long params_load_addr,
+		       unsigned int setup_data_offset)
+{
+#ifdef CONFIG_KEXEC_KHO
+	struct setup_data *sd = (void *)params + setup_data_offset;
+	struct kho_data *kho = (void *)sd + sizeof(*sd);
+
+	sd->type = SETUP_KEXEC_KHO;
+	sd->len = sizeof(struct kho_data);
+
+	/* Only add if we have all KHO images in place */
+	if (!image->kho.dt.buffer || !image->kho.mem_cache.buffer)
+		return;
+
+	/* Add setup data */
+	kho->dt_addr = image->kho.dt.mem;
+	kho->dt_size = image->kho.dt.bufsz;
+	kho->scratch_addr = kho_scratch_phys;
+	kho->scratch_size = kho_scratch_len;
+	kho->mem_cache_addr = image->kho.mem_cache.mem;
+	kho->mem_cache_size = image->kho.mem_cache.bufsz;
+	sd->next = params->hdr.setup_data;
+	params->hdr.setup_data = params_load_addr + setup_data_offset;
+#endif /* CONFIG_KEXEC_KHO */
+}
+
 static int
 setup_boot_parameters(struct kimage *image, struct boot_params *params,
 		      unsigned long params_load_addr,
@@ -305,6 +333,13 @@ setup_boot_parameters(struct kimage *image, struct boot_params *params,
 				     sizeof(struct ima_setup_data);
 	}
 
+	if (IS_ENABLED(CONFIG_KEXEC_KHO)) {
+		/* Setup space to store preservation metadata */
+		setup_kho(image, params, params_load_addr, setup_data_offset);
+		setup_data_offset += sizeof(struct setup_data) +
+				     sizeof(struct kho_data);
+	}
+
 	/* Setup RNG seed */
 	setup_rng_seed(params, params_load_addr, setup_data_offset);
 
@@ -470,6 +505,10 @@ static void *bzImage64_load(struct kimage *image, char *kernel,
 		kbuf.bufsz += sizeof(struct setup_data) +
 			      sizeof(struct ima_setup_data);
 
+	if (IS_ENABLED(CONFIG_KEXEC_KHO))
+		kbuf.bufsz += sizeof(struct setup_data) +
+			      sizeof(struct kho_data);
+
 	params = kzalloc(kbuf.bufsz, GFP_KERNEL);
 	if (!params)
 		return ERR_PTR(-ENOMEM);
diff --git a/arch/x86/kernel/setup.c b/arch/x86/kernel/setup.c
index 1526747bedf2..196414c9c9e6 100644
--- a/arch/x86/kernel/setup.c
+++ b/arch/x86/kernel/setup.c
@@ -382,6 +382,29 @@ int __init ima_get_kexec_buffer(void **addr, size_t *size)
 }
 #endif
 
+static void __init add_kho(u64 phys_addr, u32 data_len)
+{
+#ifdef CONFIG_KEXEC_KHO
+	struct kho_data *kho;
+	u64 addr = phys_addr + sizeof(struct setup_data);
+	u64 size = data_len - sizeof(struct setup_data);
+
+	kho = early_memremap(addr, size);
+	if (!kho) {
+		pr_warn("setup: failed to memremap kho data (0x%llx, 0x%llx)\n",
+			 addr, size);
+		return;
+	}
+
+	kho_populate(kho->dt_addr, kho->scratch_addr, kho->scratch_size,
+		     kho->mem_cache_addr, kho->mem_cache_size);
+
+	early_memunmap(kho, size);
+#else
+	pr_warn("Passed KHO data, but CONFIG_KEXEC_KHO not set. Ignoring.\n");
+#endif
+}
+
 static void __init parse_setup_data(void)
 {
 	struct setup_data *data;
@@ -410,6 +433,9 @@ static void __init parse_setup_data(void)
 		case SETUP_IMA:
 			add_early_ima_buffer(pa_data);
 			break;
+		case SETUP_KEXEC_KHO:
+			add_kho(pa_data, data_len);
+			break;
 		case SETUP_RNG_SEED:
 			data = early_memremap(pa_data, data_len);
 			add_bootloader_randomness(data->data, data->len);
@@ -989,8 +1015,26 @@ void __init setup_arch(char **cmdline_p)
 	cleanup_highmap();
 
 	memblock_set_current_limit(ISA_END_ADDRESS);
+
 	e820__memblock_setup();
 
+	/*
+	 * We can resize memblocks at this point, let's dump all KHO
+	 * reservations in and switch from scratch-only to normal allocations
+	 */
+	kho_reserve_mem();
+
+	/* Allocations now skip scratch mem, return low 1M to the pool */
+	if (is_kho_boot()) {
+		u64 i;
+		phys_addr_t base, end;
+
+		__for_each_mem_range(i, &memblock.memory, NULL, NUMA_NO_NODE,
+				     MEMBLOCK_SCRATCH, &base, &end, NULL)
+			if (end <= ISA_END_ADDRESS)
+				memblock_clear_scratch(base, end - base);
+	}
+
 	/*
 	 * Needs to run after memblock setup because it needs the physical
 	 * memory size.
@@ -1106,6 +1150,8 @@ void __init setup_arch(char **cmdline_p)
 	 */
 	arch_reserve_crashkernel();
 
+	kho_reserve();
+
 	memblock_find_dma_reserve();
 
 	if (!early_xdbc_setup_hardware())
diff --git a/arch/x86/mm/init_32.c b/arch/x86/mm/init_32.c
index b63403d7179d..6c3810afed04 100644
--- a/arch/x86/mm/init_32.c
+++ b/arch/x86/mm/init_32.c
@@ -20,6 +20,7 @@
 #include <linux/smp.h>
 #include <linux/init.h>
 #include <linux/highmem.h>
+#include <linux/kexec.h>
 #include <linux/pagemap.h>
 #include <linux/pci.h>
 #include <linux/pfn.h>
@@ -738,6 +739,12 @@ void __init mem_init(void)
 	after_bootmem = 1;
 	x86_init.hyper.init_after_bootmem();
 
+	/*
+	 * Now that all KHO pages are marked as reserved, let's flip them back
+	 * to normal pages with accurate refcount.
+	 */
+	kho_populate_refcount();
+
 	/*
 	 * Check boundaries twice: Some fundamental inconsistencies can
 	 * be detected at build time already.
diff --git a/arch/x86/mm/init_64.c b/arch/x86/mm/init_64.c
index a190aae8ceaf..3ce1a4767610 100644
--- a/arch/x86/mm/init_64.c
+++ b/arch/x86/mm/init_64.c
@@ -20,6 +20,7 @@
 #include <linux/smp.h>
 #include <linux/init.h>
 #include <linux/initrd.h>
+#include <linux/kexec.h>
 #include <linux/pagemap.h>
 #include <linux/memblock.h>
 #include <linux/proc_fs.h>
@@ -1339,6 +1340,12 @@ void __init mem_init(void)
 	after_bootmem = 1;
 	x86_init.hyper.init_after_bootmem();
 
+	/*
+	 * Now that all KHO pages are marked as reserved, let's flip them back
+	 * to normal pages with accurate refcount.
+	 */
+	kho_populate_refcount();
+
 	/*
 	 * Must be done after boot memory is put on freelist, because here we
 	 * might set fields in deferred struct pages that have not yet been
-- 
2.40.1


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