[XEN PATCH v3 04/16] x86: introduce CONFIG_ALTP2M Kconfig option

[Sergiy Kibrik <Sergiy_Kibrik@xxxxxxxx>]

Add new option to make altp2m code inclusion optional.
Currently altp2m implemented for Intel EPT only, so option is dependant on VMX.
Also the prompt itself depends on EXPERT=y, so that option is available
for fine-tuning, if one want to play around with it.

Use this option instead of more generic CONFIG_HVM option.
That implies the possibility to build hvm code without altp2m support,
hence we need to declare altp2m routines for hvm code to compile successfully
(altp2m_vcpu_initialise(), altp2m_vcpu_destroy(), altp2m_vcpu_enable_ve())

Also guard altp2m routines, so that they can be disabled completely in the
build -- when target platform does not actually support altp2m
(AMD-V & ARM as of now).

Signed-off-by: Sergiy Kibrik <Sergiy_Kibrik@xxxxxxxx>
CC: Tamas K Lengyel <tamas@xxxxxxxxxxxxx>
CC: Jan Beulich <jbeulich@xxxxxxxx>
CC: Stefano Stabellini <sstabellini@xxxxxxxxxx>
---
changes in v3:
 - added help text
 - use conditional prompt depending on EXPERT=y
 - corrected & extended patch description
 - put a blank line before #ifdef CONFIG_ALTP2M
 - sqashed in a separate patch for guarding altp2m code with CONFIG_ALTP2M 
option
changes in v2:
 - use separate CONFIG_ALTP2M option instead of CONFIG_VMX
---
 xen/arch/x86/Kconfig               | 11 +++++++++++
 xen/arch/x86/include/asm/altp2m.h  |  5 ++++-
 xen/arch/x86/include/asm/hvm/hvm.h |  2 +-
 xen/arch/x86/include/asm/p2m.h     | 17 ++++++++++++++++-
 xen/arch/x86/mm/Makefile           |  2 +-
 5 files changed, 33 insertions(+), 4 deletions(-)

diff --git a/xen/arch/x86/Kconfig b/xen/arch/x86/Kconfig
index 8c9f8431f0..4a35c43dc5 100644
--- a/xen/arch/x86/Kconfig
+++ b/xen/arch/x86/Kconfig
@@ -358,6 +358,17 @@ config REQUIRE_NX
          was unavailable. However, if enabled, Xen will no longer boot on
          any CPU which is lacking NX support.
 
+config ALTP2M
+       bool "Alternate P2M support" if EXPERT
+       default y
+       depends on VMX
+       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.
+
 endmenu
 
 source "common/Kconfig"
diff --git a/xen/arch/x86/include/asm/altp2m.h 
b/xen/arch/x86/include/asm/altp2m.h
index 2d36c5aa9b..effbef51eb 100644
--- a/xen/arch/x86/include/asm/altp2m.h
+++ b/xen/arch/x86/include/asm/altp2m.h
@@ -7,7 +7,7 @@
 #ifndef __ASM_X86_ALTP2M_H
 #define __ASM_X86_ALTP2M_H
 
-#ifdef CONFIG_HVM
+#ifdef CONFIG_ALTP2M
 
 #include <xen/types.h>
 #include <xen/sched.h>         /* for struct vcpu, struct domain */
@@ -34,6 +34,9 @@ static inline bool altp2m_active(const struct domain *d)
 }
 
 /* Only declaration is needed. DCE will optimise it out when linking. */
+void altp2m_vcpu_initialise(struct vcpu *v);
+void altp2m_vcpu_destroy(struct vcpu *v);
+int altp2m_vcpu_enable_ve(struct vcpu *v, gfn_t gfn);
 void altp2m_vcpu_disable_ve(struct vcpu *v);
 
 #endif
diff --git a/xen/arch/x86/include/asm/hvm/hvm.h 
b/xen/arch/x86/include/asm/hvm/hvm.h
index 1c01e22c8e..2ebea1a92c 100644
--- a/xen/arch/x86/include/asm/hvm/hvm.h
+++ b/xen/arch/x86/include/asm/hvm/hvm.h
@@ -670,7 +670,7 @@ static inline bool hvm_hap_supported(void)
 /* returns true if hardware supports alternate p2m's */
 static inline bool hvm_altp2m_supported(void)
 {
-    return hvm_funcs.caps.altp2m;
+    return IS_ENABLED(CONFIG_ALTP2M) && hvm_funcs.caps.altp2m;
 }
 
 /* Returns true if we have the minimum hardware requirements for nested virt */
diff --git a/xen/arch/x86/include/asm/p2m.h b/xen/arch/x86/include/asm/p2m.h
index c1478ffc36..b247aa4c7d 100644
--- a/xen/arch/x86/include/asm/p2m.h
+++ b/xen/arch/x86/include/asm/p2m.h
@@ -577,10 +577,10 @@ static inline gfn_t mfn_to_gfn(const struct domain *d, 
mfn_t mfn)
         return _gfn(mfn_x(mfn));
 }
 
-#ifdef CONFIG_HVM
 #define AP2MGET_prepopulate true
 #define AP2MGET_query false
 
+#ifdef CONFIG_ALTP2M
 /*
  * Looks up altp2m entry. If the entry is not found it looks up the entry in
  * hostp2m.
@@ -589,6 +589,15 @@ static inline gfn_t mfn_to_gfn(const struct domain *d, 
mfn_t mfn)
 int altp2m_get_effective_entry(struct p2m_domain *ap2m, gfn_t gfn, mfn_t *mfn,
                                p2m_type_t *t, p2m_access_t *a,
                                bool prepopulate);
+#else
+static inline int altp2m_get_effective_entry(struct p2m_domain *ap2m,
+                                             gfn_t gfn, mfn_t *mfn,
+                                             p2m_type_t *t, p2m_access_t *a,
+                                             bool prepopulate)
+{
+    ASSERT_UNREACHABLE();
+    return -EOPNOTSUPP;
+}
 #endif
 
 /* Init the datastructures for later use by the p2m code */
@@ -914,8 +923,14 @@ static inline bool p2m_set_altp2m(struct vcpu *v, unsigned 
int idx)
 /* Switch alternate p2m for a single vcpu */
 bool p2m_switch_vcpu_altp2m_by_id(struct vcpu *v, unsigned int idx);
 
+#ifdef CONFIG_ALTP2M
 /* Check to see if vcpu should be switched to a different p2m. */
 void p2m_altp2m_check(struct vcpu *v, uint16_t idx);
+#else
+static inline void p2m_altp2m_check(struct vcpu *v, uint16_t idx)
+{
+}
+#endif
 
 /* Flush all the alternate p2m's for a domain */
 void p2m_flush_altp2m(struct domain *d);
diff --git a/xen/arch/x86/mm/Makefile b/xen/arch/x86/mm/Makefile
index 0128ca7ab6..d7d57b8190 100644
--- a/xen/arch/x86/mm/Makefile
+++ b/xen/arch/x86/mm/Makefile
@@ -1,7 +1,7 @@
 obj-y += shadow/
 obj-$(CONFIG_HVM) += hap/
 
-obj-$(CONFIG_HVM) += altp2m.o
+obj-$(CONFIG_ALTP2M) += altp2m.o
 obj-$(CONFIG_HVM) += guest_walk_2.o guest_walk_3.o guest_walk_4.o
 obj-$(CONFIG_SHADOW_PAGING) += guest_walk_4.o
 obj-$(CONFIG_MEM_ACCESS) += mem_access.o
-- 
2.25.1