[PATCH 8/8] pdx: Add CONFIG_HAS_PDX_COMPRESSION as a Kconfig option

[Alejandro Vallejo <alejandro.vallejo@xxxxxxxxx>]

Adds a new compile-time flag to allow disabling pdx compression and
compiles out compression-related code/data. It also shorts the pdx<->pfn
conversion macros and creates stubs for masking fucntions.

Signed-off-by: Alejandro Vallejo <alejandro.vallejo@xxxxxxxxx>
---
 xen/arch/x86/domain.c | 19 +++++++++++++------
 xen/common/Kconfig    | 10 ++++++++++
 xen/common/pdx.c      | 15 +++++++++++----
 xen/include/xen/pdx.h | 34 ++++++++++++++++++++++++++++++++++
 4 files changed, 68 insertions(+), 10 deletions(-)

diff --git a/xen/arch/x86/domain.c b/xen/arch/x86/domain.c
index 39c2153165..c818ccc4d5 100644
--- a/xen/arch/x86/domain.c
+++ b/xen/arch/x86/domain.c
@@ -458,7 +458,7 @@ void domain_cpu_policy_changed(struct domain *d)
     }
 }
 
-#ifndef CONFIG_BIGMEM
+#if !defined(CONFIG_BIGMEM) && defined(CONFIG_HAS_PDX_COMPRESSION)
 /*
  * The hole may be at or above the 44-bit boundary, so we need to determine
  * the total bit count until reaching 32 significant (not squashed out) bits
@@ -485,13 +485,20 @@ static unsigned int __init noinline 
_domain_struct_bits(void)
 struct domain *alloc_domain_struct(void)
 {
     struct domain *d;
-#ifdef CONFIG_BIGMEM
-    const unsigned int bits = 0;
-#else
+
     /*
-     * We pack the PDX of the domain structure into a 32-bit field within
-     * the page_info structure. Hence the MEMF_bits() restriction.
+     * Without CONFIG_BIGMEM, we pack the PDX of the domain structure into
+     * a 32-bit field within the page_info structure. Hence the MEMF_bits()
+     * restriction. With PDX compression in place the number of bits must
+     * be calculated at runtime, but it's fixed otherwise.
+     *
+     * On systems with CONFIG_BIGMEM there's no packing, and so there's no
+     * such restriction.
      */
+#if defined(CONFIG_BIGMEM) || !defined(CONFIG_HAS_PDX_COMPRESSION)
+    const unsigned int bits = IS_ENABLED(CONFIG_BIGMEM) ? 0 :
+                                                          32 + PAGE_SHIFT;
+#else
     static unsigned int __read_mostly bits;
 
     if ( unlikely(!bits) )
diff --git a/xen/common/Kconfig b/xen/common/Kconfig
index 40ec63c4b2..6605a60ff7 100644
--- a/xen/common/Kconfig
+++ b/xen/common/Kconfig
@@ -23,6 +23,16 @@ config GRANT_TABLE
 
          If unsure, say Y.
 
+config HAS_PDX_COMPRESSION
+       bool "PDX (Page inDeX) compression support"
+       default ARM
+       help
+         PDX compression is a technique that allows the hypervisor to
+         represent physical addresses in a very space-efficient manner.
+         This is very helpful reducing memory wastage in systems with
+         memory banks with base addresses far from each other, but carrier
+         a performance cost.
+
 config ALTERNATIVE_CALL
        bool
 
diff --git a/xen/common/pdx.c b/xen/common/pdx.c
index cc963a3cb3..d0fac9d7c7 100644
--- a/xen/common/pdx.c
+++ b/xen/common/pdx.c
@@ -31,11 +31,15 @@ unsigned long __read_mostly pdx_group_valid[BITS_TO_LONGS(
 
 bool __mfn_valid(unsigned long mfn)
 {
-    if ( unlikely(evaluate_nospec(mfn >= max_page)) )
+    bool invalid = mfn >= max_page;
+#ifdef CONFIG_HAS_PDX_COMPRESSION
+    invalid |= mfn & pfn_hole_mask;
+#endif
+
+    if ( unlikely(evaluate_nospec(invalid)) )
         return false;
-    return likely(!(mfn & pfn_hole_mask)) &&
-           likely(test_bit(pfn_to_pdx(mfn) / PDX_GROUP_COUNT,
-                           pdx_group_valid));
+
+    return test_bit(pfn_to_pdx(mfn) / PDX_GROUP_COUNT, pdx_group_valid);
 }
 
 void set_pdx_range(unsigned long smfn, unsigned long emfn)
@@ -49,6 +53,8 @@ void set_pdx_range(unsigned long smfn, unsigned long emfn)
         __set_bit(idx, pdx_group_valid);
 }
 
+#ifdef CONFIG_HAS_PDX_COMPRESSION
+
 /*
  * Diagram to make sense of the following variables. The masks and shifts
  * are done on mfn values in order to convert to/from pdx:
@@ -178,6 +184,7 @@ void __init pfn_pdx_hole_setup(unsigned long mask)
     pfn_top_mask        = ~(pfn_pdx_bottom_mask | pfn_hole_mask);
     ma_top_mask         = pfn_top_mask << PAGE_SHIFT;
 }
+#endif /* CONFIG_HAS_PDX_COMPRESSION */
 
 
 /*
diff --git a/xen/include/xen/pdx.h b/xen/include/xen/pdx.h
index ce27177b56..5531890d1c 100644
--- a/xen/include/xen/pdx.h
+++ b/xen/include/xen/pdx.h
@@ -98,6 +98,8 @@ bool __mfn_valid(unsigned long mfn);
 #define mfn_to_pdx(mfn) pfn_to_pdx(mfn_x(mfn))
 #define pdx_to_mfn(pdx) _mfn(pdx_to_pfn(pdx))
 
+#ifdef CONFIG_HAS_PDX_COMPRESSION
+
 extern unsigned long pfn_pdx_bottom_mask, ma_va_bottom_mask;
 extern unsigned int pfn_pdx_hole_shift;
 extern unsigned long pfn_hole_mask;
@@ -225,7 +227,39 @@ static inline uint64_t directmapoff_to_maddr(unsigned long 
offset)
  *             position marks a potentially compressible bit.
  */
 void pfn_pdx_hole_setup(unsigned long mask);
+#else /* CONFIG_HAS_PDX_COMPRESSION */
+
+/* Without PDX compression we can skip some computations */
+
+/* pdx<->pfn == identity */
+#define pdx_to_pfn(x) (x)
+#define pfn_to_pdx(x) (x)
+
+/* directmap is indexed by by maddr */
+#define maddr_to_directmapoff(x) (x)
+#define directmapoff_to_maddr(x) (x)
+
+static inline bool pdx_is_region_compressible(unsigned long smfn,
+                                              unsigned long emfn)
+{
+    return true;
+}
+
+static inline uint64_t pdx_init_mask(uint64_t base_addr)
+{
+    return 0;
+}
+
+static inline uint64_t pdx_region_mask(uint64_t base, uint64_t len)
+{
+    return 0;
+}
+
+static inline void pfn_pdx_hole_setup(unsigned long mask)
+{
+}
 
+#endif /* CONFIG_HAS_PDX_COMPRESSION */
 #endif /* __XEN_PDX_H__ */
 
 /*
-- 
2.34.1