[PATCH RFC] x86+libxl: correct p2m (shadow) memory pool size calculation

[Jan Beulich <jbeulich@xxxxxxxx>]

The reference "to shadow the resident processes" is applicable to
domains (potentially) running in shadow mode only. Adjust the
calculations accordingly.

In dom0_paging_pages() also take the opportunity and stop open-coding
DIV_ROUND_UP().

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
---
RFC: I'm pretty sure I can't change a public libxl function (deprecated
     or not) like this, but I also don't know how I should go about
     doing so (short of introducing a brand new function and leaving the
     existing one broken).

--- a/tools/include/libxl_utils.h
+++ b/tools/include/libxl_utils.h
@@ -23,7 +23,10 @@ const
 #endif
 char *libxl_basename(const char *name); /* returns string from strdup */
 
-unsigned long libxl_get_required_shadow_memory(unsigned long maxmem_kb, 
unsigned int smp_cpus);
+unsigned long libxl_get_required_shadow_memory(unsigned long maxmem_kb,
+                                               unsigned int smp_cpus,
+                                               libxl_domain_type type,
+                                               bool hap);
   /* deprecated; see LIBXL_HAVE_DOMAIN_NEED_MEMORY_CONFIG in libxl.h */
 int libxl_name_to_domid(libxl_ctx *ctx, const char *name, uint32_t *domid);
 int libxl_domain_qualifier_to_domid(libxl_ctx *ctx, const char *name, uint32_t 
*domid);
--- a/tools/libs/light/libxl_create.c
+++ b/tools/libs/light/libxl_create.c
@@ -1194,10 +1194,17 @@ int libxl__domain_config_setdefault(libx
     }
 
     if (d_config->b_info.shadow_memkb == LIBXL_MEMKB_DEFAULT
-        && ok_to_default_memkb_in_create(gc))
+        && ok_to_default_memkb_in_create(gc)) {
+        bool hap = d_config->c_info.type != LIBXL_DOMAIN_TYPE_PV
+                   ? libxl_defbool_val(d_config->c_info.hap)
+                   : false;
+
         d_config->b_info.shadow_memkb =
             libxl_get_required_shadow_memory(d_config->b_info.max_memkb,
-                                             d_config->b_info.max_vcpus);
+                                             d_config->b_info.max_vcpus,
+                                             d_config->c_info.type,
+                                             hap);
+    }
 
     /* No IOMMU reservation is needed if passthrough mode is not 'sync_pt' */
     if (d_config->b_info.iommu_memkb == LIBXL_MEMKB_DEFAULT
--- a/tools/libs/light/libxl_utils.c
+++ b/tools/libs/light/libxl_utils.c
@@ -36,15 +36,21 @@ char *libxl_basename(const char *name)
     return strdup(name);
 }
 
-unsigned long libxl_get_required_shadow_memory(unsigned long maxmem_kb, 
unsigned int smp_cpus)
+unsigned long libxl_get_required_shadow_memory(unsigned long maxmem_kb,
+                                               unsigned int smp_cpus,
+                                               libxl_domain_type type,
+                                               bool hap)
 {
     /* 256 pages (1MB) per vcpu,
-       plus 1 page per MiB of RAM for the P2M map,
-       plus 1 page per MiB of RAM to shadow the resident processes.
+       plus 1 page per MiB of RAM for the P2M map (for non-PV guests),
+       plus 1 page per MiB of RAM to shadow the resident processes (for shadow
+       mode guests).
        This is higher than the minimum that Xen would allocate if no value
        were given (but the Xen minimum is for safety, not performance).
      */
-    return 4 * (256 * smp_cpus + 2 * (maxmem_kb / 1024));
+    return 4 * (256 * smp_cpus +
+                ((type != LIBXL_DOMAIN_TYPE_PV) + !hap) *
+                (maxmem_kb / 1024));
 }
 
 char *libxl_domid_to_name(libxl_ctx *ctx, uint32_t domid)
--- a/xen/arch/x86/dom0_build.c
+++ b/xen/arch/x86/dom0_build.c
@@ -317,9 +317,12 @@ unsigned long __init dom0_paging_pages(c
     /* Copied from: libxl_get_required_shadow_memory() */
     unsigned long memkb = nr_pages * (PAGE_SIZE / 1024);
 
-    memkb = 4 * (256 * d->max_vcpus + 2 * (memkb / 1024));
+    memkb = 4 * (256 * d->max_vcpus +
+                 (paging_mode_enabled(d) +
+                  (opt_dom0_shadow || opt_pv_l1tf_hwdom)) *
+                 (memkb / 1024));
 
-    return ((memkb + 1023) / 1024) << (20 - PAGE_SHIFT);
+    return DIV_ROUND_UP(memkb, 1024) << (20 - PAGE_SHIFT);
 }