[PATCH 1/5] libxl: remove separate calculation of IOMMU memory overhead

[Paul Durrant <paul@xxxxxxx>]

From: Paul Durrant <pdurrant@xxxxxxxxxx>

When using 'shared_pt' mode the IOMMU is using the EPT PTEs. In 'sync_pt'
mode these PTEs are instead replicated for the IOMMU to use. Hence, it is
fairly clear that the memory overhead in this mode is essentially another
copy of the P2M.

This patch removes the independent calculation done in
libxl__get_required_iommu_memory() and instead simply uses 'shadow_memkb'
as the value of the IOMMU overhead since this is the estimated size of
the P2M.

Signed-off-by: Paul Durrant <pdurrant@xxxxxxxxxx>
---
Cc: Ian Jackson <iwj@xxxxxxxxxxxxxx>
Cc: Wei Liu <wl@xxxxxxx>
Cc: Anthony PERARD <anthony.perard@xxxxxxxxxx>
---
 tools/libs/light/libxl_create.c | 22 +++++-----------------
 1 file changed, 5 insertions(+), 17 deletions(-)

diff --git a/tools/libs/light/libxl_create.c b/tools/libs/light/libxl_create.c
index 9a6e92b3a5..f07ba84850 100644
--- a/tools/libs/light/libxl_create.c
+++ b/tools/libs/light/libxl_create.c
@@ -1001,21 +1001,6 @@ static bool ok_to_default_memkb_in_create(libxl__gc *gc)
      */
 }
 
-static unsigned long libxl__get_required_iommu_memory(unsigned long maxmem_kb)
-{
-    unsigned long iommu_pages = 0, mem_pages = maxmem_kb / 4;
-    unsigned int level;
-
-    /* Assume a 4 level page table with 512 entries per level */
-    for (level = 0; level < 4; level++)
-    {
-        mem_pages = DIV_ROUNDUP(mem_pages, 512);
-        iommu_pages += mem_pages;
-    }
-
-    return iommu_pages * 4;
-}
-
 int libxl__domain_config_setdefault(libxl__gc *gc,
                                     libxl_domain_config *d_config,
                                     uint32_t domid /* for logging, only */)
@@ -1168,12 +1153,15 @@ int libxl__domain_config_setdefault(libxl__gc *gc,
             libxl_get_required_shadow_memory(d_config->b_info.max_memkb,
                                              d_config->b_info.max_vcpus);
 
-    /* No IOMMU reservation is needed if passthrough mode is not 'sync_pt' */
+    /* No IOMMU reservation is needed if passthrough mode is not 'sync_pt'
+     * otherwise we need a reservation sufficient to accommodate a copy of
+     * the P2M.
+     */
     if (d_config->b_info.iommu_memkb == LIBXL_MEMKB_DEFAULT
         && ok_to_default_memkb_in_create(gc))
         d_config->b_info.iommu_memkb =
             (d_config->c_info.passthrough == LIBXL_PASSTHROUGH_SYNC_PT)
-            ? libxl__get_required_iommu_memory(d_config->b_info.max_memkb)
+            ? d_config->b_info.shadow_memkb
             : 0;
 
     ret = libxl__domain_build_info_setdefault(gc, &d_config->b_info);
-- 
2.20.1