[PATCH] x86/shadow: Fix PV32 shadowing in !HVM builds

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

The OSSTest bisector identified an issue with c/s 1894049fa283 ("x86/shadow:
L2H shadow type is PV32-only") in !HVM builds.

The bug is ultimately caused by sh_type_to_size[] not actually being specific
to HVM guests, and it's position in shadow/hvm.c mislead the reasoning.

To fix the issue that OSSTest identified, SH_type_l2h_64_shadow must still
have the value 1 in any CONFIG_PV32 build.  But simply adjusting this leaves
us with misleading logic, and a reasonable chance of making a related error
again in the future.

In hindsight, moving sh_type_to_size[] out of common.c in the first place a
mistake.  Therefore, move sh_type_to_size[] back to living in common.c,
leaving a comment explaining why it happens to be inside an HVM conditional.

This effectively reverts the second half of 4fec945409fc ("x86/shadow: adjust
and move sh_type_to_size[]") while retaining the other improvements from the
same changeset.

While making this change, also adjust the sh_type_to_size[] declaration to
match its definition.

Fixes: 4fec945409fc ("x86/shadow: adjust and move sh_type_to_size[]")
Fixes: 1894049fa283 ("x86/shadow: L2H shadow type is PV32-only")
Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
---
CC: Jan Beulich <JBeulich@xxxxxxxx>
CC: Roger Pau Monné <roger.pau@xxxxxxxxxx>
CC: Wei Liu <wl@xxxxxxx>
CC: George Dunlap <george.dunlap@xxxxxxxxxxxxx>
CC: Tim Deegan <tim@xxxxxxx>

I was unsure whether it was reasonable to move the table back into its old
position but it can live pretty much anywhere in common.c as far as I'm
concerned.
---
 xen/arch/x86/mm/shadow/common.c  | 38 ++++++++++++++++++++++++++++++++++++++
 xen/arch/x86/mm/shadow/hvm.c     | 31 -------------------------------
 xen/arch/x86/mm/shadow/private.h |  2 +-
 3 files changed, 39 insertions(+), 32 deletions(-)

diff --git a/xen/arch/x86/mm/shadow/common.c b/xen/arch/x86/mm/shadow/common.c
index 26901b8b3bcf..a74b15e3e75b 100644
--- a/xen/arch/x86/mm/shadow/common.c
+++ b/xen/arch/x86/mm/shadow/common.c
@@ -39,6 +39,44 @@
 #include <public/sched.h>
 #include "private.h"
 
+/*
+ * This table shows the allocation behaviour of the different modes:
+ *
+ * Xen paging      64b  64b  64b
+ * Guest paging    32b  pae  64b
+ * PV or HVM       HVM  HVM   *
+ * Shadow paging   pae  pae  64b
+ *
+ * sl1 size         8k   4k   4k
+ * sl2 size        16k   4k   4k
+ * sl3 size         -    -    4k
+ * sl4 size         -    -    4k
+ *
+ * Note: our accessor, shadow_size(), can optimise out this table in PV-only
+ * builds.
+ */
+#ifdef CONFIG_HVM
+const uint8_t sh_type_to_size[] = {
+    [SH_type_l1_32_shadow]   = 2,
+    [SH_type_fl1_32_shadow]  = 2,
+    [SH_type_l2_32_shadow]   = 4,
+    [SH_type_l1_pae_shadow]  = 1,
+    [SH_type_fl1_pae_shadow] = 1,
+    [SH_type_l2_pae_shadow]  = 1,
+    [SH_type_l1_64_shadow]   = 1,
+    [SH_type_fl1_64_shadow]  = 1,
+    [SH_type_l2_64_shadow]   = 1,
+#ifdef CONFIG_PV32
+    [SH_type_l2h_64_shadow]  = 1,
+#endif
+    [SH_type_l3_64_shadow]   = 1,
+    [SH_type_l4_64_shadow]   = 1,
+    [SH_type_p2m_table]      = 1,
+    [SH_type_monitor_table]  = 1,
+    [SH_type_oos_snapshot]   = 1,
+};
+#endif /* CONFIG_HVM */
+
 DEFINE_PER_CPU(uint32_t,trace_shadow_path_flags);
 
 static int cf_check sh_enable_log_dirty(struct domain *, bool log_global);
diff --git a/xen/arch/x86/mm/shadow/hvm.c b/xen/arch/x86/mm/shadow/hvm.c
index 918865cf1b6a..88c3c16322f2 100644
--- a/xen/arch/x86/mm/shadow/hvm.c
+++ b/xen/arch/x86/mm/shadow/hvm.c
@@ -33,37 +33,6 @@
 
 #include "private.h"
 
-/*
- * This table shows the allocation behaviour of the different modes:
- *
- * Xen paging      64b  64b  64b
- * Guest paging    32b  pae  64b
- * PV or HVM       HVM  HVM   *
- * Shadow paging   pae  pae  64b
- *
- * sl1 size         8k   4k   4k
- * sl2 size        16k   4k   4k
- * sl3 size         -    -    4k
- * sl4 size         -    -    4k
- */
-const uint8_t sh_type_to_size[] = {
-    [SH_type_l1_32_shadow]   = 2,
-    [SH_type_fl1_32_shadow]  = 2,
-    [SH_type_l2_32_shadow]   = 4,
-    [SH_type_l1_pae_shadow]  = 1,
-    [SH_type_fl1_pae_shadow] = 1,
-    [SH_type_l2_pae_shadow]  = 1,
-    [SH_type_l1_64_shadow]   = 1,
-    [SH_type_fl1_64_shadow]  = 1,
-    [SH_type_l2_64_shadow]   = 1,
-/*  [SH_type_l2h_64_shadow]  = 1,  PV32-only */
-    [SH_type_l3_64_shadow]   = 1,
-    [SH_type_l4_64_shadow]   = 1,
-    [SH_type_p2m_table]      = 1,
-    [SH_type_monitor_table]  = 1,
-    [SH_type_oos_snapshot]   = 1,
-};
-
 /**************************************************************************/
 /* x86 emulator support for the shadow code
  */
diff --git a/xen/arch/x86/mm/shadow/private.h b/xen/arch/x86/mm/shadow/private.h
index 7d6c846c8037..79d82364fc92 100644
--- a/xen/arch/x86/mm/shadow/private.h
+++ b/xen/arch/x86/mm/shadow/private.h
@@ -362,7 +362,7 @@ static inline int mfn_oos_may_write(mfn_t gmfn)
 #endif /* (SHADOW_OPTIMIZATIONS & SHOPT_OUT_OF_SYNC) */
 
 /* Figure out the size (in pages) of a given shadow type */
-extern const u8 sh_type_to_size[SH_type_unused];
+extern const uint8_t sh_type_to_size[SH_type_unused];
 static inline unsigned int
 shadow_size(unsigned int shadow_type)
 {
-- 
2.11.0