xen: add configurable max domain size

Add a config option to set the max size of a Xen domain.  This is used
to scale the size of the physical-to-machine array; it ends up using
around 1 page/GByte, so there's no reason to be very restrictive.

For a 32-bit guest, the default value of 8GB is probably sufficient;
there's not much point in giving a 32-bit machine much more memory
than that.

Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

3 files changed, 25 insertions, 13 deletions

diff --git a/arch/x86/xen/Kconfig b/arch/x86/xen/Kconfig
index 525b108411bd..d0f1c7c5dc3d 100644
--- a/arch/x86/xen/Kconfig
+++ b/arch/x86/xen/Kconfig
@@ -11,3 +11,13 @@ config XEN
           This is the Linux Xen port.  Enabling this will allow the
           kernel to boot in a paravirtualized environment under the
           Xen hypervisor.
+
+config XEN_MAX_DOMAIN_MEMORY
+       int "Maximum allowed size of a domain in gigabytes"
+       default 8
+       depends on XEN
+       help
+         The pseudo-physical to machine address array is sized
+         according to the maximum possible memory size of a Xen
+         domain.  This array uses 1 page per gigabyte, so there's no
+         need to be too stingy here.
\ No newline at end of file
diff --git a/arch/x86/xen/mmu.c b/arch/x86/xen/mmu.c
index c3b27dec6f03..644232aa7bfb 100644
--- a/arch/x86/xen/mmu.c
+++ b/arch/x86/xen/mmu.c
@@ -56,19 +56,13 @@
 #include "multicalls.h"
 #include "mmu.h"
 
-/*
- * This should probably be a config option.  On 32-bit, it costs 1
- * page/gig of memory; on 64-bit its 2 pages/gig.  If we want it to be
- * completely unbounded we can add another level to the p2m structure.
- */
-#define MAX_GUEST_PAGES         (16ull * 1024*1024*1024 / PAGE_SIZE)
 #define P2M_ENTRIES_PER_PAGE    (PAGE_SIZE / sizeof(unsigned long))
 
-static unsigned long *p2m_top[MAX_GUEST_PAGES / P2M_ENTRIES_PER_PAGE];
+static unsigned long *p2m_top[MAX_DOMAIN_PAGES / P2M_ENTRIES_PER_PAGE];
 
 static inline unsigned p2m_top_index(unsigned long pfn)
 {
-        BUG_ON(pfn >= MAX_GUEST_PAGES);
+        BUG_ON(pfn >= MAX_DOMAIN_PAGES);
         return pfn / P2M_ENTRIES_PER_PAGE;
 }
 
@@ -81,12 +75,9 @@ void __init xen_build_dynamic_phys_to_machine(void)
 {
         unsigned pfn;
         unsigned long *mfn_list = (unsigned long *)xen_start_info->mfn_list;
+        unsigned long max_pfn = min(MAX_DOMAIN_PAGES, xen_start_info->nr_pages);
 
-        BUG_ON(xen_start_info->nr_pages >= MAX_GUEST_PAGES);
-
-        for(pfn = 0;
-            pfn < xen_start_info->nr_pages;
-            pfn += P2M_ENTRIES_PER_PAGE) {
+        for(pfn = 0; pfn < max_pfn; pfn += P2M_ENTRIES_PER_PAGE) {
                 unsigned topidx = p2m_top_index(pfn);
 
                 p2m_top[topidx] = &mfn_list[pfn];
@@ -97,6 +88,9 @@ unsigned long get_phys_to_machine(unsigned long pfn)
 {
         unsigned topidx, idx;
 
+        if (unlikely(pfn >= MAX_DOMAIN_PAGES))
+                return INVALID_P2M_ENTRY;
+
         topidx = p2m_top_index(pfn);
         if (p2m_top[topidx] == NULL)
                 return INVALID_P2M_ENTRY;
@@ -129,6 +123,11 @@ void set_phys_to_machine(unsigned long pfn, unsigned long mfn)
                 return;
         }
 
+        if (unlikely(pfn >= MAX_DOMAIN_PAGES)) {
+                BUG_ON(mfn != INVALID_P2M_ENTRY);
+                return;
+        }
+
         topidx = p2m_top_index(pfn);
         if (p2m_top[topidx] == NULL) {
                 /* no need to allocate a page to store an invalid entry */
diff --git a/arch/x86/xen/setup.c b/arch/x86/xen/setup.c
index 37f8f0b8f743..488447878a9d 100644
--- a/arch/x86/xen/setup.c
+++ b/arch/x86/xen/setup.c
@@ -16,6 +16,7 @@
 #include <asm/xen/hypervisor.h>
 #include <asm/xen/hypercall.h>
 
+#include <xen/page.h>
 #include <xen/interface/callback.h>
 #include <xen/interface/physdev.h>
 #include <xen/features.h>
@@ -36,6 +37,8 @@ char * __init xen_memory_setup(void)
 {
         unsigned long max_pfn = xen_start_info->nr_pages;
 
+        max_pfn = min(MAX_DOMAIN_PAGES, max_pfn);
+
         e820.nr_map = 0;
         add_memory_region(0, LOWMEMSIZE(), E820_RAM);
         add_memory_region(HIGH_MEMORY, PFN_PHYS(max_pfn)-HIGH_MEMORY, E820_RAM);