[PATCH v2 07/32] kho: add interfaces to unpreserve folios and physical memory ranges

[Pasha Tatashin <pasha.tatashin@soleen.com>]

From: Changyuan Lyu <changyuanl@google.com>

Allow users of KHO to cancel the previous preservation by adding the
necessary interfaces to unpreserve folio.

Signed-off-by: Changyuan Lyu <changyuanl@google.com>
Co-developed-by: Pasha Tatashin <pasha.tatashin@soleen.com>
Signed-off-by: Pasha Tatashin <pasha.tatashin@soleen.com>
---
 include/linux/kexec_handover.h | 12 +++++
 kernel/kexec_handover.c        | 90 +++++++++++++++++++++++++++++-----
 2 files changed, 89 insertions(+), 13 deletions(-)

diff --git a/include/linux/kexec_handover.h b/include/linux/kexec_handover.h
index cabdff5f50a2..383e9460edb9 100644
--- a/include/linux/kexec_handover.h
+++ b/include/linux/kexec_handover.h
@@ -33,7 +33,9 @@ struct folio;
 bool kho_is_enabled(void);
 
 int kho_preserve_folio(struct folio *folio);
+int kho_unpreserve_folio(struct folio *folio);
 int kho_preserve_phys(phys_addr_t phys, size_t size);
+int kho_unpreserve_phys(phys_addr_t phys, size_t size);
 struct folio *kho_restore_folio(phys_addr_t phys);
 int kho_add_subtree(const char *name, void *fdt);
 void kho_remove_subtree(void *fdt);
@@ -58,11 +60,21 @@ static inline int kho_preserve_folio(struct folio *folio)
 	return -EOPNOTSUPP;
 }
 
+static inline int kho_unpreserve_folio(struct folio *folio)
+{
+	return -EOPNOTSUPP;
+}
+
 static inline int kho_preserve_phys(phys_addr_t phys, size_t size)
 {
 	return -EOPNOTSUPP;
 }
 
+static inline int kho_unpreserve_phys(phys_addr_t phys, size_t size)
+{
+	return -EOPNOTSUPP;
+}
+
 static inline struct folio *kho_restore_folio(phys_addr_t phys)
 {
 	return NULL;
diff --git a/kernel/kexec_handover.c b/kernel/kexec_handover.c
index 30d673f7f68a..26ad926912a7 100644
--- a/kernel/kexec_handover.c
+++ b/kernel/kexec_handover.c
@@ -136,26 +136,33 @@ static void *xa_load_or_alloc(struct xarray *xa, unsigned long index, size_t sz)
 	return elm;
 }
 
-static void __kho_unpreserve(struct kho_mem_track *track, unsigned long pfn,
-			     unsigned long end_pfn)
+static void __kho_unpreserve_order(struct kho_mem_track *track, unsigned long pfn,
+				   unsigned int order)
 {
 	struct kho_mem_phys_bits *bits;
 	struct kho_mem_phys *physxa;
+	const unsigned long pfn_high = pfn >> order;
 
-	while (pfn < end_pfn) {
-		const unsigned int order =
-			min(count_trailing_zeros(pfn), ilog2(end_pfn - pfn));
-		const unsigned long pfn_high = pfn >> order;
+	physxa = xa_load(&track->orders, order);
+	if (!physxa)
+		return;
 
-		physxa = xa_load(&track->orders, order);
-		if (!physxa)
-			continue;
+	bits = xa_load(&physxa->phys_bits, pfn_high / PRESERVE_BITS);
+	if (!bits)
+		return;
 
-		bits = xa_load(&physxa->phys_bits, pfn_high / PRESERVE_BITS);
-		if (!bits)
-			continue;
+	clear_bit(pfn_high % PRESERVE_BITS, bits->preserve);
+}
 
-		clear_bit(pfn_high % PRESERVE_BITS, bits->preserve);
+static void __kho_unpreserve(struct kho_mem_track *track, unsigned long pfn,
+			     unsigned long end_pfn)
+{
+	unsigned int order;
+
+	while (pfn < end_pfn) {
+		order = min(count_trailing_zeros(pfn), ilog2(end_pfn - pfn));
+
+		__kho_unpreserve_order(track, pfn, order);
 
 		pfn += 1 << order;
 	}
@@ -667,6 +674,30 @@ int kho_preserve_folio(struct folio *folio)
 }
 EXPORT_SYMBOL_GPL(kho_preserve_folio);
 
+/**
+ * kho_unpreserve_folio - unpreserve a folio.
+ * @folio: folio to unpreserve.
+ *
+ * Instructs KHO to unpreserve a folio that was preserved by
+ * kho_preserve_folio() before. The provided @folio (pfn and order)
+ * must exactly match a previously preserved folio.
+ *
+ * Return: 0 on success, error code on failure
+ */
+int kho_unpreserve_folio(struct folio *folio)
+{
+	const unsigned long pfn = folio_pfn(folio);
+	const unsigned int order = folio_order(folio);
+	struct kho_mem_track *track = &kho_out.track;
+
+	if (kho_out.finalized)
+		return -EBUSY;
+
+	__kho_unpreserve_order(track, pfn, order);
+	return 0;
+}
+EXPORT_SYMBOL_GPL(kho_unpreserve_folio);
+
 /**
  * kho_preserve_phys - preserve a physically contiguous range across kexec.
  * @phys: physical address of the range.
@@ -712,6 +743,39 @@ int kho_preserve_phys(phys_addr_t phys, size_t size)
 }
 EXPORT_SYMBOL_GPL(kho_preserve_phys);
 
+/**
+ * kho_unpreserve_phys - unpreserve a physically contiguous range.
+ * @phys: physical address of the range.
+ * @size: size of the range.
+ *
+ * Instructs KHO to unpreserve the memory range from @phys to @phys + @size.
+ * The @phys address must be aligned to @size, and @size must be a
+ * power-of-2 multiple of PAGE_SIZE.
+ * This call must exactly match a granularity at which memory was originally
+ * preserved (either by a `kho_preserve_phys` call with the same `phys` and
+ * `size`). Unpreserving arbitrary sub-ranges of larger preserved blocks is not
+ * supported.
+ *
+ * Return: 0 on success, error code on failure
+ */
+int kho_unpreserve_phys(phys_addr_t phys, size_t size)
+{
+	struct kho_mem_track *track = &kho_out.track;
+	unsigned long pfn = PHYS_PFN(phys);
+	unsigned long end_pfn = PHYS_PFN(phys + size);
+
+	if (kho_out.finalized)
+		return -EBUSY;
+
+	if (!PAGE_ALIGNED(phys) || !PAGE_ALIGNED(size))
+		return -EINVAL;
+
+	__kho_unpreserve(track, pfn, end_pfn);
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(kho_unpreserve_phys);
+
 static int __kho_abort(void)
 {
 	int err = 0;
-- 
2.50.0.727.gbf7dc18ff4-goog