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

* [PATCH RFC] x86+libxl: correct p2m (shadow) memory pool size calculation
@ 2022-04-22 10:57 Jan Beulich
  2022-04-22 11:10 ` Juergen Gross
  2022-04-22 11:14 ` Roger Pau Monné
  0 siblings, 2 replies; 5+ messages in thread
From: Jan Beulich @ 2022-04-22 10:57 UTC (permalink / raw)
  To: xen-devel
  Cc: Andrew Cooper, Wei Liu, Roger Pau Monné,
	Anthony Perard, Juergen Gross

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@suse.com>
---
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);
 }
 
 



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