mm: convert track_pfn_insert() to pfnmap_setup_cachemode*()

...  by factoring it out from track_pfn_remap() into
pfnmap_setup_cachemode() and provide pfnmap_setup_cachemode_pfn() as a
replacement for track_pfn_insert().

For PMDs/PUDs, we keep checking a single pfn only.  Add some
documentation, and also document why it is valid to not check the whole
pfn range.

We'll reuse pfnmap_setup_cachemode() from core MM next.

Link: https://lkml.kernel.org/r/20250512123424.637989-3-david@redhat.com
Signed-off-by: David Hildenbrand <david@redhat.com>
Acked-by: Ingo Molnar <mingo@kernel.org>	[x86 bits]
Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Reviewed-by: Liam R. Howlett <Liam.Howlett@oracle.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Borislav Betkov <bp@alien8.de>
Cc: Dave Airlie <airlied@gmail.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Jani Nikula <jani.nikula@linux.intel.com>
Cc: Jann Horn <jannh@google.com>
Cc: Jonas Lahtinen <joonas.lahtinen@linux.intel.com>
Cc: "Masami Hiramatsu (Google)" <mhiramat@kernel.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Peter Xu <peterx@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Thomas Gleinxer <tglx@linutronix.de>
Cc: Tvrtko Ursulin <tursulin@ursulin.net>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

1 files changed, 44 insertions, 8 deletions

diff --git a/include/linux/pgtable.h b/include/linux/pgtable.h
index f1e890b60460..be1745839871 100644
--- a/include/linux/pgtable.h
+++ b/include/linux/pgtable.h
@@ -1496,13 +1496,10 @@ static inline int track_pfn_remap(struct vm_area_struct *vma, pgprot_t *prot,
 	return 0;
 }
 
-/*
- * track_pfn_insert is called when a _new_ single pfn is established
- * by vmf_insert_pfn().
- */
-static inline void track_pfn_insert(struct vm_area_struct *vma, pgprot_t *prot,
-				    pfn_t pfn)
+static inline int pfnmap_setup_cachemode(unsigned long pfn, unsigned long size,
+		pgprot_t *prot)
 {
+	return 0;
 }
 
 /*
@@ -1552,8 +1549,32 @@ static inline void untrack_pfn_clear(struct vm_area_struct *vma)
 extern int track_pfn_remap(struct vm_area_struct *vma, pgprot_t *prot,
 			   unsigned long pfn, unsigned long addr,
 			   unsigned long size);
-extern void track_pfn_insert(struct vm_area_struct *vma, pgprot_t *prot,
-			     pfn_t pfn);
+
+/**
+ * pfnmap_setup_cachemode - setup the cachemode in the pgprot for a pfn range
+ * @pfn: the start of the pfn range
+ * @size: the size of the pfn range in bytes
+ * @prot: the pgprot to modify
+ *
+ * Lookup the cachemode for the pfn range starting at @pfn with the size
+ * @size and store it in @prot, leaving other data in @prot unchanged.
+ *
+ * This allows for a hardware implementation to have fine-grained control of
+ * memory cache behavior at page level granularity. Without a hardware
+ * implementation, this function does nothing.
+ *
+ * Currently there is only one implementation for this - x86 Page Attribute
+ * Table (PAT). See Documentation/arch/x86/pat.rst for more details.
+ *
+ * This function can fail if the pfn range spans pfns that require differing
+ * cachemodes. If the pfn range was previously verified to have a single
+ * cachemode, it is sufficient to query only a single pfn. The assumption is
+ * that this is the case for drivers using the vmf_insert_pfn*() interface.
+ *
+ * Returns 0 on success and -EINVAL on error.
+ */
+int pfnmap_setup_cachemode(unsigned long pfn, unsigned long size,
+		pgprot_t *prot);
 extern int track_pfn_copy(struct vm_area_struct *dst_vma,
 		struct vm_area_struct *src_vma, unsigned long *pfn);
 extern void untrack_pfn_copy(struct vm_area_struct *dst_vma,
@@ -1563,6 +1584,21 @@ extern void untrack_pfn(struct vm_area_struct *vma, unsigned long pfn,
 extern void untrack_pfn_clear(struct vm_area_struct *vma);
 #endif
 
+/**
+ * pfnmap_setup_cachemode_pfn - setup the cachemode in the pgprot for a pfn
+ * @pfn: the pfn
+ * @prot: the pgprot to modify
+ *
+ * Lookup the cachemode for @pfn and store it in @prot, leaving other
+ * data in @prot unchanged.
+ *
+ * See pfnmap_setup_cachemode() for details.
+ */
+static inline void pfnmap_setup_cachemode_pfn(unsigned long pfn, pgprot_t *prot)
+{
+	pfnmap_setup_cachemode(pfn, PAGE_SIZE, prot);
+}
+
 #ifdef CONFIG_MMU
 #ifdef __HAVE_COLOR_ZERO_PAGE
 static inline int is_zero_pfn(unsigned long pfn)