Gitlab Randconfig found:

  arch/x86/mm/shadow/common.c: In function 'shadow_prealloc':
  arch/x86/mm/shadow/common.c:1023:18: error: implicit declaration of function
      'paging_logdirty_levels'; did you mean 'paging_log_dirty_init'? [-Werror=implicit-function-declaration]
   1023 |         count += paging_logdirty_levels();
        |                  ^~~~~~~~~~~~~~~~~~~~~~
        |                  paging_log_dirty_init
  arch/x86/mm/shadow/common.c:1023:18: error: nested extern declaration of 'paging_logdirty_levels' [-Werror=nested-externs]

Move the declaration outside of #if PG_log_dirty.

Fixes: 33fb3a661223 ("x86/shadow: account for log-dirty mode when pre-allocating")
Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
---
CC: Jan Beulich <JBeulich@suse.com>
CC: Roger Pau Monné <roger.pau@citrix.com>
CC: Wei Liu <wl@xen.org>

An alternative would be to double paging_logdirty_levels() up in the else
case, returning 0.  The underlying logc in shadow_prealloc() succumbs to DCE
either way.
---
 xen/arch/x86/include/asm/paging.h | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/xen/arch/x86/include/asm/paging.h b/xen/arch/x86/include/asm/paging.h
index 38bec8af2ed1..2ca22f20adff 100644
--- a/xen/arch/x86/include/asm/paging.h
+++ b/xen/arch/x86/include/asm/paging.h
@@ -149,6 +149,10 @@ struct paging_mode {
 /*****************************************************************************
  * Log dirty code */
 
+#define paging_logdirty_levels() \
+    (DIV_ROUND_UP(PADDR_BITS - PAGE_SHIFT - (PAGE_SHIFT + 3), \
+                  PAGE_SHIFT - ilog2(sizeof(mfn_t))) + 1)
+
 #if PG_log_dirty
 
 /* get the dirty bitmap for a specific range of pfns */
@@ -187,10 +191,6 @@ bool paging_mfn_is_dirty(const struct domain *d, mfn_t gmfn);
 #define L4_LOGDIRTY_IDX(pfn) ((pfn_x(pfn) >> (PAGE_SHIFT + 3 + PAGETABLE_ORDER * 2)) & \
                               (LOGDIRTY_NODE_ENTRIES-1))
 
-#define paging_logdirty_levels() \
-    (DIV_ROUND_UP(PADDR_BITS - PAGE_SHIFT - (PAGE_SHIFT + 3), \
-                  PAGE_SHIFT - ilog2(sizeof(mfn_t))) + 1)
-
 #ifdef CONFIG_HVM
 /* VRAM dirty tracking support */
 struct sh_dirty_vram {
-- 
2.30.2

On 24.03.2023 00:46, Andrew Cooper wrote:
> Gitlab Randconfig found:
> 
>   arch/x86/mm/shadow/common.c: In function 'shadow_prealloc':
>   arch/x86/mm/shadow/common.c:1023:18: error: implicit declaration of function
>       'paging_logdirty_levels'; did you mean 'paging_log_dirty_init'? [-Werror=implicit-function-declaration]
>    1023 |         count += paging_logdirty_levels();
>         |                  ^~~~~~~~~~~~~~~~~~~~~~
>         |                  paging_log_dirty_init
>   arch/x86/mm/shadow/common.c:1023:18: error: nested extern declaration of 'paging_logdirty_levels' [-Werror=nested-externs]

Okay, that's SHADOW_PAGING && !HVM && PV_SHIM_EXCLUSIVE - I can see
how I missed to test that case.

> Move the declaration outside of #if PG_log_dirty.
> 
> Fixes: 33fb3a661223 ("x86/shadow: account for log-dirty mode when pre-allocating")
> Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>

Reviewed-by: Jan Beulich <jbeulich@suse.com>

> An alternative would be to double paging_logdirty_levels() up in the else
> case, returning 0.  The underlying logc in shadow_prealloc() succumbs to DCE
> either way.

I think I prefer the way you have it.

Jan