[PATCH v1 6/7] xen/mem_access: wrap memory access when VM_EVENT=n

[Penny Zheng <Penny.Zheng@xxxxxxx>]

Feature memory access is based on vm event subsystem, and it could be disabled
in the future. So a few switch-blocks in do_altp2m_op() need
IS_ENABLED(CONFIG_VM_EVENT) wrapping to pass compilation when ALTP2M=y and
VM_EVENT=n(, hence MEM_ACCESS=n), like HVMOP_altp2m_set_mem_access, etc.
Function p2m_mem_access_check() still needs stub when VM_EVENT=n to
pass compilation.
Although local variable "req_ptr" still remains NULL throughout its lifetime,
with the change of NULL assignment, we will face runtime undefined error only
when CONFIG_USBAN is on. So we strengthen the condition check via adding
vm_event_is_enabled() for the special case.

Signed-off-by: Penny Zheng <Penny.Zheng@xxxxxxx>
---
v3 -> v4:
- a new commit split from previous "xen/vm_event: consolidate CONFIG_VM_EVENT"
- use IS_ENABLED() to replace #ifdef
- remove unnecessary changes in compat_altp2m_op()
- strengthen the condition check to fix runtime undefined error when
CONFIG_USBAN=y
---
 xen/arch/x86/hvm/hvm.c                | 97 +++++++++++++++------------
 xen/arch/x86/include/asm/mem_access.h | 10 +++
 2 files changed, 65 insertions(+), 42 deletions(-)

diff --git a/xen/arch/x86/hvm/hvm.c b/xen/arch/x86/hvm/hvm.c
index ebadcf2289..c3417b0593 100644
--- a/xen/arch/x86/hvm/hvm.c
+++ b/xen/arch/x86/hvm/hvm.c
@@ -52,6 +52,7 @@
 #include <asm/i387.h>
 #include <asm/mc146818rtc.h>
 #include <asm/mce.h>
+#include <asm/mem_access.h>
 #include <asm/monitor.h>
 #include <asm/msr.h>
 #include <asm/mtrr.h>
@@ -2081,7 +2082,7 @@ int hvm_hap_nested_page_fault(paddr_t gpa, unsigned long 
gla,
 #endif
     }
 
-    if ( req_ptr )
+    if ( req_ptr && vm_event_is_enabled(curr) )
     {
         if ( monitor_traps(curr, sync, req_ptr) < 0 )
             rc = 0;
@@ -4862,58 +4863,70 @@ static int do_altp2m_op(
         break;
 
     case HVMOP_altp2m_set_mem_access:
-        if ( a.u.mem_access.pad )
-            rc = -EINVAL;
-        else
-            rc = p2m_set_mem_access(d, _gfn(a.u.mem_access.gfn), 1, 0, 0,
-                                    a.u.mem_access.access,
-                                    a.u.mem_access.view);
+        if ( IS_ENABLED(CONFIG_VM_EVENT) )
+        {
+            if ( a.u.mem_access.pad )
+                rc = -EINVAL;
+            else
+                rc = p2m_set_mem_access(d, _gfn(a.u.mem_access.gfn), 1, 0, 0,
+                                        a.u.mem_access.access,
+                                        a.u.mem_access.view);
+        }
         break;
 
     case HVMOP_altp2m_set_mem_access_multi:
-        if ( a.u.set_mem_access_multi.pad ||
-             a.u.set_mem_access_multi.opaque > a.u.set_mem_access_multi.nr )
+        if ( IS_ENABLED(CONFIG_VM_EVENT) )
         {
-            rc = -EINVAL;
-            break;
-        }
+            if ( a.u.set_mem_access_multi.pad ||
+                 a.u.set_mem_access_multi.opaque >
+                    a.u.set_mem_access_multi.nr )
+            {
+                rc = -EINVAL;
+                break;
+            }
 
-        /*
-         * Unlike XENMEM_access_op_set_access_multi, we don't need any bits of
-         * the 'continuation' counter to be zero (to stash a command in).
-         * However, 0x40 is a good 'stride' to make sure that we make
-         * a reasonable amount of forward progress before yielding,
-         * so use a mask of 0x3F here.
-         */
-        rc = p2m_set_mem_access_multi(d, a.u.set_mem_access_multi.pfn_list,
-                                      a.u.set_mem_access_multi.access_list,
-                                      a.u.set_mem_access_multi.nr,
-                                      a.u.set_mem_access_multi.opaque,
-                                      0x3F,
-                                      a.u.set_mem_access_multi.view);
-        if ( rc > 0 )
-        {
-            a.u.set_mem_access_multi.opaque = rc;
-            rc = -ERESTART;
-            if ( __copy_field_to_guest(guest_handle_cast(arg, 
xen_hvm_altp2m_op_t),
-                                       &a, u.set_mem_access_multi.opaque) )
-                rc = -EFAULT;
+            /*
+             * Unlike XENMEM_access_op_set_access_multi, we don't need any
+             * bits of the 'continuation' counter to be zero (to stash a
+             * command in).
+             * However, 0x40 is a good 'stride' to make sure that we make
+             * a reasonable amount of forward progress before yielding,
+             * so use a mask of 0x3F here.
+             */
+            rc = p2m_set_mem_access_multi(d, a.u.set_mem_access_multi.pfn_list,
+                                          a.u.set_mem_access_multi.access_list,
+                                          a.u.set_mem_access_multi.nr,
+                                          a.u.set_mem_access_multi.opaque,
+                                          0x3F,
+                                          a.u.set_mem_access_multi.view);
+            if ( rc > 0 )
+            {
+                a.u.set_mem_access_multi.opaque = rc;
+                rc = -ERESTART;
+                if ( __copy_field_to_guest(
+                        guest_handle_cast(arg, xen_hvm_altp2m_op_t),
+                        &a, u.set_mem_access_multi.opaque) )
+                    rc = -EFAULT;
+            }
         }
         break;
 
     case HVMOP_altp2m_get_mem_access:
-        if ( a.u.mem_access.pad )
-            rc = -EINVAL;
-        else
+        if ( IS_ENABLED(CONFIG_VM_EVENT) )
         {
-            xenmem_access_t access;
-
-            rc = p2m_get_mem_access(d, _gfn(a.u.mem_access.gfn), &access,
-                                    a.u.mem_access.view);
-            if ( !rc )
+            if ( a.u.mem_access.pad )
+                rc = -EINVAL;
+            else
             {
-                a.u.mem_access.access = access;
-                rc = __copy_to_guest(arg, &a, 1) ? -EFAULT : 0;
+                xenmem_access_t access;
+
+                rc = p2m_get_mem_access(d, _gfn(a.u.mem_access.gfn), &access,
+                                        a.u.mem_access.view);
+                if ( !rc )
+                {
+                    a.u.mem_access.access = access;
+                    rc = __copy_to_guest(arg, &a, 1) ? -EFAULT : 0;
+                }
             }
         }
         break;
diff --git a/xen/arch/x86/include/asm/mem_access.h 
b/xen/arch/x86/include/asm/mem_access.h
index 257ed33de1..790bed81e8 100644
--- a/xen/arch/x86/include/asm/mem_access.h
+++ b/xen/arch/x86/include/asm/mem_access.h
@@ -14,6 +14,7 @@
 #ifndef __ASM_X86_MEM_ACCESS_H__
 #define __ASM_X86_MEM_ACCESS_H__
 
+#ifdef CONFIG_VM_EVENT
 /*
  * Setup vm_event request based on the access (gla is -1ull if not available).
  * Handles the rw2rx conversion. Boolean return value indicates if event type
@@ -25,6 +26,15 @@
 bool p2m_mem_access_check(paddr_t gpa, unsigned long gla,
                           struct npfec npfec,
                           struct vm_event_st **req_ptr);
+#else
+static inline bool p2m_mem_access_check(paddr_t gpa, unsigned long gla,
+                                        struct npfec npfec,
+                                        struct vm_event_st **req_ptr)
+{
+    *req_ptr = NULL;
+    return false;
+}
+#endif /* CONFIG_VM_EVENT */
 
 /* Check for emulation and mark vcpu for skipping one instruction
  * upon rescheduling if required. */
-- 
2.34.1