[PATCH 2/8] pdx: introduce function to calculate max PFN based on PDX compression

[Roger Pau Monne <roger.pau@xxxxxxxxxx>]

This is the code already present and used by x86 in setup_max_pdx(), which
takes into account the current PDX compression, plus the limitation of the
virtual memory layout to return the maximum usable PFN in the system,
possibly truncating the input PFN provided by the caller.

This helper will be used by upcoming PDX related changes that introduce a
new compression algorithm.

Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
---
 xen/arch/x86/setup.c  | 19 ++-----------------
 xen/common/pdx.c      | 25 +++++++++++++++++++++++++
 xen/include/xen/pdx.h |  8 ++++++++
 3 files changed, 35 insertions(+), 17 deletions(-)

diff --git a/xen/arch/x86/setup.c b/xen/arch/x86/setup.c
index 1f5cb67bd0ee..ea670567cbf7 100644
--- a/xen/arch/x86/setup.c
+++ b/xen/arch/x86/setup.c
@@ -721,23 +721,8 @@ static uint64_t __init consider_modules(
 
 static void __init setup_max_pdx(unsigned long top_page)
 {
-    max_pdx = pfn_to_pdx(top_page - 1) + 1;
-
-    if ( max_pdx > (DIRECTMAP_SIZE >> PAGE_SHIFT) )
-        max_pdx = DIRECTMAP_SIZE >> PAGE_SHIFT;
-
-    if ( max_pdx > FRAMETABLE_NR )
-        max_pdx = FRAMETABLE_NR;
-
-    if ( max_pdx > MPT_VIRT_SIZE / sizeof(unsigned long) )
-        max_pdx = MPT_VIRT_SIZE / sizeof(unsigned long);
-
-#ifdef PAGE_LIST_NULL
-    if ( max_pdx >= PAGE_LIST_NULL )
-        max_pdx = PAGE_LIST_NULL - 1;
-#endif
-
-    max_page = pdx_to_pfn(max_pdx - 1) + 1;
+    max_page = get_max_pfn(top_page);
+    max_pdx = pfn_to_pdx(max_page - 1) + 1;
 }
 
 /* A temporary copy of the e820 map that we can mess with during bootstrap. */
diff --git a/xen/common/pdx.c b/xen/common/pdx.c
index b8384e6189df..3004c5f28bdd 100644
--- a/xen/common/pdx.c
+++ b/xen/common/pdx.c
@@ -55,6 +55,31 @@ void set_pdx_range(unsigned long smfn, unsigned long emfn)
         __set_bit(idx, pdx_group_valid);
 }
 
+unsigned long get_max_pfn(unsigned long top_pfn)
+{
+    unsigned long pdx = pfn_to_pdx(top_pfn - 1) + 1;
+
+#ifdef DIRECTMAP_SIZE
+    if ( pdx > (DIRECTMAP_SIZE >> PAGE_SHIFT) )
+        pdx = DIRECTMAP_SIZE >> PAGE_SHIFT;
+#endif
+
+    if ( pdx > FRAMETABLE_NR )
+        pdx = FRAMETABLE_NR;
+
+#ifdef MPT_VIRT_SIZE
+    if ( pdx > MPT_VIRT_SIZE / sizeof(unsigned long) )
+        pdx = MPT_VIRT_SIZE / sizeof(unsigned long);
+#endif
+
+#ifdef PAGE_LIST_NULL
+    if ( pdx >= PAGE_LIST_NULL )
+        pdx = PAGE_LIST_NULL - 1;
+#endif
+
+    return pdx_to_pfn(pdx - 1) + 1;
+}
+
 #ifdef CONFIG_PDX_COMPRESSION
 
 /*
diff --git a/xen/include/xen/pdx.h b/xen/include/xen/pdx.h
index 9faeea3ac9f2..0f580853cb2e 100644
--- a/xen/include/xen/pdx.h
+++ b/xen/include/xen/pdx.h
@@ -92,6 +92,14 @@ void set_pdx_range(unsigned long smfn, unsigned long emfn);
  */
 bool __mfn_valid(unsigned long mfn);
 
+/**
+ * Get maximum usable PFN given the virtual address space restrictions.
+ *
+ * @param pdx Maximum PFN
+ * @return Possibly truncated maximum PFN
+ */
+unsigned long get_max_pfn(unsigned long top_pfn);
+
 #define page_to_pdx(pg)  ((pg) - frame_table)
 #define pdx_to_page(pdx) gcc11_wrap(frame_table + (pdx))
 
-- 
2.49.0