[Xen-devel] [PATCH 2/4] xen: arm: move magic pfns out of guest RAM region

[Ian Campbell <ian.campbell@xxxxxxxxxx>]

Because toolstacks (at least libxl) only allow RAM to be specified in 1M
increments these two pages were effectively costing 1M of guest RAM space.

Since these pages don't actually need to live in RAM just move them out.

With this a guest can now use the full 768M of the address space reserved
for RAM. (ok, not that impressive, but it simplifies things later)

Signed-off-by: Ian Campbell <ian.campbell@xxxxxxxxxx>
---
 tools/libxc/xc_dom_arm.c      |   10 +++++-----
 xen/include/public/arch-arm.h |    2 ++
 2 files changed, 7 insertions(+), 5 deletions(-)

diff --git a/tools/libxc/xc_dom_arm.c b/tools/libxc/xc_dom_arm.c
index c085b4a..36b1487 100644
--- a/tools/libxc/xc_dom_arm.c
+++ b/tools/libxc/xc_dom_arm.c
@@ -58,12 +58,12 @@ static int setup_pgtables_arm(struct xc_dom_image *dom)
 static int alloc_magic_pages(struct xc_dom_image *dom)
 {
     int rc, i;
+    const xen_pfn_t base = GUEST_MAGIC_BASE >> PAGE_SHIFT;
     xen_pfn_t p2m[NR_MAGIC_PAGES];
-
     DOMPRINTF_CALLED(dom->xch);
 
     for (i = 0; i < NR_MAGIC_PAGES; i++)
-        p2m[i] = dom->rambase_pfn + dom->total_pages + i;
+        p2m[i] = base + i;
 
     rc = xc_domain_populate_physmap_exact(
             dom->xch, dom->guest_domid, NR_MAGIC_PAGES,
@@ -71,8 +71,8 @@ static int alloc_magic_pages(struct xc_dom_image *dom)
     if ( rc < 0 )
         return rc;
 
-    dom->console_pfn = dom->rambase_pfn + dom->total_pages + 
CONSOLE_PFN_OFFSET;
-    dom->xenstore_pfn = dom->rambase_pfn + dom->total_pages + 
XENSTORE_PFN_OFFSET;
+    dom->console_pfn = base + CONSOLE_PFN_OFFSET;
+    dom->xenstore_pfn = base + XENSTORE_PFN_OFFSET;
 
     xc_clear_domain_page(dom->xch, dom->guest_domid, dom->console_pfn);
     xc_clear_domain_page(dom->xch, dom->guest_domid, dom->xenstore_pfn);
@@ -262,7 +262,7 @@ int arch_setup_meminit(struct xc_dom_image *dom)
     const uint64_t modsize = dtb_size + ramdisk_size;
     const uint64_t ram128mb = rambase + (128<<20);
 
-    if ( ramend - 1 > GUEST_RAM_END - NR_MAGIC_PAGES*XC_PAGE_SIZE )
+    if ( ramend - 1 > GUEST_RAM_END )
     {
         DOMPRINTF("%s: ram size is too large for guest address space: "
                   "%"PRIx64" > %"PRIx64,
diff --git a/xen/include/public/arch-arm.h b/xen/include/public/arch-arm.h
index dc11040..b860da5 100644
--- a/xen/include/public/arch-arm.h
+++ b/xen/include/public/arch-arm.h
@@ -375,6 +375,8 @@ typedef uint64_t xen_callback_t;
 #define GUEST_GNTTAB_BASE 0xb0000000ULL
 #define GUEST_GNTTAB_SIZE 0x00020000ULL
 
+#define GUEST_MAGIC_BASE  0xc0000000ULL
+
 /* Interrupts */
 #define GUEST_TIMER_VIRT_PPI    27
 #define GUEST_TIMER_PHYS_S_PPI  29
-- 
1.7.10.4


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