[RFC PATCH v2 6/7] pmpool: Restore state from device tree post-kexec

[Stanislav Kinsburskii <skinsburskii@linux.microsoft.com>]

From: Stanislav Kinsburskii <stanislav.kinsburskii@gmail.com>

Retrieve the pmpool bitmap from metadata in the fdt passed over kexec,
bypassing the need for reinitialization. This ensures the seamless transfer
of the pmpool state across kexec.

Signed-off-by: Stanislav Kinsburskii <skinsburskii@linux.microsoft.com>
---
 mm/pmpool.c |   46 ++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 46 insertions(+)

diff --git a/mm/pmpool.c b/mm/pmpool.c
index f2173db782d6..6c1a28fd3493 100644
--- a/mm/pmpool.c
+++ b/mm/pmpool.c
@@ -9,6 +9,7 @@
 #include <linux/libfdt.h>
 #include <linux/memblock.h>
 #include <linux/mm.h>
+#include <linux/of.h>
 #include <linux/pmpool.h>
 
 #include "cma.h"
@@ -49,11 +50,56 @@ static void pmpool_fixup_cma(struct cma *cma)
 	pr_info("CMA bitmap moved to %#llx\n", virt_to_phys(cma->bitmap));
 }
 
+static int pmpool_fdt_restore(struct cma *cma)
+{
+	struct device_node *dn;
+	u64 val;
+
+	dn = of_find_compatible_node(NULL, NULL, "pmpool");
+	if (!dn)
+		return -ENOENT;
+
+	if (of_property_read_u64(dn, "base", &val)) {
+		pr_err("invalid fdt: no base\n");
+		return -EINVAL;
+	}
+	if (val != PFN_PHYS(cma->base_pfn)) {
+		pr_err("fdt base doesn't match: %#llx != %#llx\n",
+			val, PFN_PHYS(cma->base_pfn));
+		return -EINVAL;
+	}
+
+	if (of_property_read_u64(dn, "size", &val)) {
+		pr_err("invalid fdt: no size\n");
+		return -EINVAL;
+	}
+	if (val != (cma->count << PAGE_SHIFT)) {
+		pr_err("fdt size doesn't match: %#llx != %#lx\n",
+			val, cma->count << PAGE_SHIFT);
+		return -EINVAL;
+	}
+
+	if (of_property_read_u64(dn, "bitmap", &val)) {
+		pr_err("invalid fdt: no bitmap\n");
+		return -EINVAL;
+	}
+
+	pr_info("CMA bitmap restored to %#llx\n", val);
+
+	bitmap_free(cma->bitmap);
+	cma->bitmap = phys_to_virt(val);
+
+	return 0;
+}
+
 static int __init default_pmpool_fixup_cma(void)
 {
 	if (!default_pmpool)
 		return 0;
 
+	if (!pmpool_fdt_restore(default_pmpool->cma))
+		return 0;
+
 	pmpool_fixup_cma(default_pmpool->cma);
 	return 0;
 }