[PATCH 2/2] x86/mm: correct PG_log_dirty definition

[Jan Beulich <jbeulich@xxxxxxxx>]

While it is correct that in shim-exclusive mode log-dirty handling is
all unreachable code, the present conditional still isn't correct: In a
HVM=n and SHADOW_PAGING=n configuration log-dirty code also is all
unreachable (and hence violating Misra rule 2.1).

As we're aiming at moving away from special casing PV_SHIM_EXCLUSIVE=y,
don't retain that part of the conditional.

Because of hypercall-defs.c we need to carry out the dependency by
introducing a new auxiliary PAGING control.

Since compiling out mm/paging.c altogether would entail further changes,
merely conditionalize the one function in there (paging_enable()) which
would otherwise remain unreachable (Misra rule 2.1 again) when PAGING=n.

Fixes: 23d4e0d17b76 ("x86/shim: fix build with PV_SHIM_EXCLUSIVE and 
SHADOW_PAGING")
Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
---
Of course PAGING is at risk of being confused with MEM_PAGING. It not
having a prompt, I hope that's tolerable, as I can't really think of a
better name.

Other PG_log_dirty pre-processor conditionals then likely also want
replacing. mm/paging.c and mm/p2m-basic.c could also be compiled out
altogether when PAGING=n, at the expense of introducing a few more
stubs.

FTAOD, the Fixes: tag being referenced does not mean this patch corrects
the far more recently introduced build issue with the combination of the
two features. That's still work that I expect Penny to carry out (with
there still being the option of reverting the final part of the earlier
series).

--- a/xen/arch/x86/Kconfig
+++ b/xen/arch/x86/Kconfig
@@ -162,6 +162,9 @@ config SHADOW_PAGING
 
           If unsure, say Y.
 
+config PAGING
+       def_bool HVM || SHADOW_PAGING
+
 config BIGMEM
        bool "big memory support"
        default n
--- a/xen/arch/x86/domctl.c
+++ b/xen/arch/x86/domctl.c
@@ -213,11 +213,15 @@ long arch_do_domctl(
     {
 
     case XEN_DOMCTL_shadow_op:
+#ifdef CONFIG_PAGING
         ret = paging_domctl(d, &domctl->u.shadow_op, u_domctl, 0);
         if ( ret == -ERESTART )
             return hypercall_create_continuation(
                        __HYPERVISOR_paging_domctl_cont, "h", u_domctl);
         copyback = true;
+#else
+        ret = -EOPNOTSUPP;
+#endif
         break;
 
     case XEN_DOMCTL_ioport_permission:
--- a/xen/arch/x86/include/asm/paging.h
+++ b/xen/arch/x86/include/asm/paging.h
@@ -55,7 +55,7 @@
 #define PG_translate   0
 #define PG_external    0
 #endif
-#if defined(CONFIG_HVM) || !defined(CONFIG_PV_SHIM_EXCLUSIVE)
+#ifdef CONFIG_PAGING
 /* Enable log dirty mode */
 #define PG_log_dirty   (XEN_DOMCTL_SHADOW_ENABLE_LOG_DIRTY << PG_mode_shift)
 #else
--- a/xen/arch/x86/mm/paging.c
+++ b/xen/arch/x86/mm/paging.c
@@ -864,6 +864,7 @@ void paging_final_teardown(struct domain
     p2m_final_teardown(d);
 }
 
+#ifdef CONFIG_PAGING
 /* Enable an arbitrary paging-assistance mode.  Call once at domain
  * creation. */
 int paging_enable(struct domain *d, u32 mode)
@@ -889,6 +890,7 @@ int paging_enable(struct domain *d, u32
     else
         return shadow_enable(d, mode);
 }
+#endif
 
 #ifdef CONFIG_HVM
 /* Called from the guest to indicate that a process is being torn down
--- a/xen/include/hypercall-defs.c
+++ b/xen/include/hypercall-defs.c
@@ -197,9 +197,11 @@ dm_op(domid_t domid, unsigned int nr_buf
 #ifdef CONFIG_SYSCTL
 sysctl(xen_sysctl_t *u_sysctl)
 #endif
+#if defined(CONFIG_X86) && defined(CONFIG_PAGING)
+paging_domctl_cont(xen_domctl_t *u_domctl)
+#endif
 #ifndef CONFIG_PV_SHIM_EXCLUSIVE
 domctl(xen_domctl_t *u_domctl)
-paging_domctl_cont(xen_domctl_t *u_domctl)
 platform_op(xen_platform_op_t *u_xenpf_op)
 #endif
 #ifdef CONFIG_HVM
@@ -296,7 +298,7 @@ dm_op                              compa
 hypfs_op                           do       do       do       do       do
 #endif
 mca                                do       do       -        -        -
-#ifndef CONFIG_PV_SHIM_EXCLUSIVE
+#if defined(CONFIG_X86) && defined(CONFIG_PAGING)
 paging_domctl_cont                 do       do       do       do       -
 #endif