[RFC PATCH v6 07/43] arm/altp2m: Introduce CONFIG_ALTP2M Kconfig option

[Rose.Spangler@xxxxxxxxxxxxxx]

From: Rose Spangler <Rose.Spangler@xxxxxxxxxxxxxx>

Following the x86 implementation in commit e96831ece819, this commit adds
the CONFIG_ALTP2M Kconfig option for ARM. This makes it possible to build
Xen without building altp2m code.

This commit also implements a stub for p2m_altp2m_check, as some
implementation is needed when CONFIG_ALTP2M is enabled. This is due to a
call to p2m_altp2m_check in vm_event.c which is gated by CONFIG_ALTP2M.

This is commit 7/8 of the preparation phase.

Signed-off-by: Rose Spangler <Rose.Spangler@xxxxxxxxxxxxxx>
Signed-off-by: Aqib Javaid <Aqib.Javaid@xxxxxxxxxxxxxx>
---
v6: Introduced this patch.
---
 xen/arch/arm/Kconfig              | 11 +++++++++++
 xen/arch/arm/altp2m.c             |  9 +++++++++
 xen/arch/arm/include/asm/altp2m.h | 18 ++++++++++++++++--
 3 files changed, 36 insertions(+), 2 deletions(-)

diff --git a/xen/arch/arm/Kconfig b/xen/arch/arm/Kconfig
index 2f2b501fdac4..fdf0721c3c03 100644
--- a/xen/arch/arm/Kconfig
+++ b/xen/arch/arm/Kconfig
@@ -98,6 +98,17 @@ config MPU
          systems supporting EL2. (UNSUPPORTED)
 endchoice
 
+config ALTP2M
+       bool "Alternate P2M support" if EXPERT
+       depends on MMU
+       default y
+       help
+         Alternate-p2m allows a guest to manage multiple p2m guest physical
+         "memory views" (as opposed to a single p2m).
+         Useful for memory introspection.
+
+         If unsure, stay with defaults.
+
 source "arch/Kconfig"
 
 config ACPI
diff --git a/xen/arch/arm/altp2m.c b/xen/arch/arm/altp2m.c
index 2bd1ff4df223..8bd174ea8f37 100644
--- a/xen/arch/arm/altp2m.c
+++ b/xen/arch/arm/altp2m.c
@@ -5,6 +5,15 @@
  * Copyright (c) 2016 Sergej Proskurin <proskurin@xxxxxxxxxxxxx>
  */
 
+#include <asm/p2m.h>
+
+/* Check to see if vcpu should be switched to a different p2m. */
+void p2m_altp2m_check(struct vcpu *v, uint16_t idx)
+{
+    /* Not yet implemented */
+    BUG();
+}
+
 /*
  * Local variables:
  * mode: C
diff --git a/xen/arch/arm/include/asm/altp2m.h 
b/xen/arch/arm/include/asm/altp2m.h
index ca836bae7330..698c35427e75 100644
--- a/xen/arch/arm/include/asm/altp2m.h
+++ b/xen/arch/arm/include/asm/altp2m.h
@@ -11,10 +11,12 @@
 
 #include <xen/sched.h>
 
+#ifdef CONFIG_ALTP2M
+
+/* Hardware always supports altp2m on ARM */
 static inline bool altp2m_supported(void)
 {
-    /* Not implemented yet */
-    return false;
+    return true;
 }
 
 /* Alternate p2m VCPU */
@@ -25,6 +27,18 @@ static inline uint16_t altp2m_vcpu_idx(const struct vcpu *v)
     return 0;
 }
 
+#else /* CONFIG_ALTP2M */
+
+static inline bool altp2m_supported(void)
+{
+    return false;
+}
+
+/* Only declaration is needed. DCE will optimise it out when linking. */
+uint16_t altp2m_vcpu_idx(const struct vcpu *v);
+
+#endif /* CONFIG_ALTP2M */
+
 #endif /* __ASM_ARM_ALTP2M_H */
 
 /*
-- 
2.34.1