[XEN][PATCH] xen/x86: guest_access: optimize raw_x_guest() for PV and HVM combinations

[Grygorii Strashko <grygorii_strashko@xxxxxxxx>]

From: Grygorii Strashko <grygorii_strashko@xxxxxxxx>

Xen uses below pattern for raw_x_guest() functions:

define raw_copy_to_guest(dst, src, len)        \
    (is_hvm_vcpu(current) ?                     \
     copy_to_user_hvm((dst), (src), (len)) :    \
     copy_to_guest_pv(dst, src, len))

How this pattern is working depends on CONFIG_PV/CONFIG_HVM as:
- PV=y and HVM=y
  Proper guest access function is selected depending on domain type.
- PV=y and HVM=n
  Only PV domains are possible. is_hvm_domain/vcpu() will constify to "false"
  and compiler will optimize code and skip HVM specific part.
- PV=n and HVM=y
  Only HVM domains are possible. is_hvm_domain/vcpu() will not be constified.
  No PV specific code will be optimized by compiler.
- PV=n and HVM=n
  No guests should possible. The code will still follow PV path.

Rework raw_x_guest() code to use required functions explicitly for each
combination of CONFIG_PV/CONFIG_HVM with main intention to optimize code for
(PV=n and HVM=y) case.

For the case (PV=n and HVM=n) empty stubs are created which return (1)
indicating failure. Hence, no guests should possible in this case -
which means no access to guest memory  should ever happen.
The two calls of __raw_copy_to_guest() in 
common/domain.c->update_runstate_area()
are fixed for this case by explicitly cast the return value to void
(MISRA C Rule 17.7).

Finally build arch/x86/usercopy.c only for PV=y.

The measured (bloat-o-meter) improvement for (PV=n and HVM=y) case is:
  add/remove: 0/10 grow/shrink: 2/90 up/down: 163/-30932 (-30769)
  Total: Before=1937113, After=1906344, chg -1.59%

Signed-off-by: Grygorii Strashko <grygorii_strashko@xxxxxxxx>
---
 xen/arch/x86/Makefile                   |  2 +-
 xen/arch/x86/include/asm/guest_access.h | 38 +++++++++++++++++++++++++
 xen/common/domain.c                     | 10 ++++---
 3 files changed, 45 insertions(+), 5 deletions(-)

diff --git a/xen/arch/x86/Makefile b/xen/arch/x86/Makefile
index 407571c510e1..27f131ffeb61 100644
--- a/xen/arch/x86/Makefile
+++ b/xen/arch/x86/Makefile
@@ -71,7 +71,7 @@ obj-y += time.o
 obj-y += traps-setup.o
 obj-y += traps.o
 obj-$(CONFIG_INTEL) += tsx.o
-obj-y += usercopy.o
+obj-$(CONFIG_PV) += usercopy.o
 obj-y += x86_emulate.o
 obj-$(CONFIG_TBOOT) += tboot.o
 obj-y += hpet.o
diff --git a/xen/arch/x86/include/asm/guest_access.h 
b/xen/arch/x86/include/asm/guest_access.h
index 69716c8b41bb..36aeb89524ab 100644
--- a/xen/arch/x86/include/asm/guest_access.h
+++ b/xen/arch/x86/include/asm/guest_access.h
@@ -13,6 +13,7 @@
 #include <asm/hvm/guest_access.h>
 
 /* Raw access functions: no type checking. */
+#if defined(CONFIG_PV) && defined(CONFIG_HVM)
 #define raw_copy_to_guest(dst, src, len)        \
     (is_hvm_vcpu(current) ?                     \
      copy_to_user_hvm((dst), (src), (len)) :    \
@@ -34,6 +35,43 @@
      copy_from_user_hvm((dst), (src), (len)) :  \
      __copy_from_guest_pv(dst, src, len))
 
+#elif defined(CONFIG_HVM)
+#define raw_copy_to_guest(dst, src, len)        \
+     copy_to_user_hvm((dst), (src), (len))
+#define raw_copy_from_guest(dst, src, len)      \
+     copy_from_user_hvm((dst), (src), (len))
+#define raw_clear_guest(dst,  len)              \
+     clear_user_hvm((dst), (len))
+#define __raw_copy_to_guest(dst, src, len)      \
+     copy_to_user_hvm((dst), (src), (len))
+#define __raw_copy_from_guest(dst, src, len)    \
+     copy_from_user_hvm((dst), (src), (len))
+
+#elif defined(CONFIG_PV)
+#define raw_copy_to_guest(dst, src, len)        \
+     copy_to_guest_pv(dst, src, len)
+#define raw_copy_from_guest(dst, src, len)      \
+     copy_from_guest_pv(dst, src, len)
+#define raw_clear_guest(dst,  len)              \
+     clear_guest_pv(dst, len)
+#define __raw_copy_to_guest(dst, src, len)      \
+     __copy_to_guest_pv(dst, src, len)
+#define __raw_copy_from_guest(dst, src, len)    \
+     __copy_from_guest_pv(dst, src, len)
+
+#else
+#define raw_copy_to_guest(dst, src, len)        \
+        ((void)(dst), (void)(src), (void)(len), 1)
+#define raw_copy_from_guest(dst, src, len)      \
+        ((void)(dst), (void)(src), (void)(len), 1)
+#define raw_clear_guest(dst, len)               \
+        ((void)(dst), (void)(len), 1)
+#define __raw_copy_to_guest(dst, src, len)      \
+        ((void)(dst), (void)(src), (void)(len), 1)
+#define __raw_copy_from_guest(dst, src, len)    \
+        ((void)(dst), (void)(src), (void)(len), 1)
+#endif
+
 /*
  * Pre-validate a guest handle.
  * Allows use of faster __copy_* functions.
diff --git a/xen/common/domain.c b/xen/common/domain.c
index 4f91316ad93e..c603edcc7d46 100644
--- a/xen/common/domain.c
+++ b/xen/common/domain.c
@@ -1985,8 +1985,9 @@ bool update_runstate_area(struct vcpu *v)
 #endif
         guest_handle--;
         runstate.state_entry_time |= XEN_RUNSTATE_UPDATE;
-        __raw_copy_to_guest(guest_handle,
-                            (void *)(&runstate.state_entry_time + 1) - 1, 1);
+        (void)__raw_copy_to_guest(guest_handle,
+                                  (void *)(&runstate.state_entry_time + 1) - 1,
+                                  1);
         smp_wmb();
     }
 
@@ -2008,8 +2009,9 @@ bool update_runstate_area(struct vcpu *v)
     {
         runstate.state_entry_time &= ~XEN_RUNSTATE_UPDATE;
         smp_wmb();
-        __raw_copy_to_guest(guest_handle,
-                            (void *)(&runstate.state_entry_time + 1) - 1, 1);
+        (void)__raw_copy_to_guest(guest_handle,
+                                  (void *)(&runstate.state_entry_time + 1) - 1,
+                                  1);
     }
 
     update_guest_memory_policy(v, &policy);
-- 
2.34.1