[Xen-devel] [PATCH 02 of 12] xen: add configurable max domain size

[Jeremy Fitzhardinge <jeremy@xxxxxxxx>]

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@xxxxxxxxxx>
---
 arch/x86/xen/Kconfig       |   10 ++++++++++
 arch/x86/xen/mmu.c         |   25 ++++++++++++-------------
 arch/x86/xen/setup.c       |    3 +++
 include/asm-x86/xen/page.h |    5 +++++
 4 files changed, 30 insertions(+), 13 deletions(-)

diff --git a/arch/x86/xen/Kconfig b/arch/x86/xen/Kconfig
--- a/arch/x86/xen/Kconfig
+++ b/arch/x86/xen/Kconfig
@@ -11,3 +11,13 @@
          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
--- 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 @@
 {
        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];
@@ -96,6 +87,9 @@
 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)
@@ -126,6 +120,11 @@
 
        if (unlikely(xen_feature(XENFEAT_auto_translated_physmap))) {
                BUG_ON(pfn != mfn && mfn != INVALID_P2M_ENTRY);
+               return;
+       }
+
+       if (unlikely(pfn >= MAX_DOMAIN_PAGES)) {
+               BUG_ON(mfn != INVALID_P2M_ENTRY);
                return;
        }
 
diff --git a/arch/x86/xen/setup.c b/arch/x86/xen/setup.c
--- 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>
@@ -35,6 +36,8 @@
 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);
diff --git a/include/asm-x86/xen/page.h b/include/asm-x86/xen/page.h
--- a/include/asm-x86/xen/page.h
+++ b/include/asm-x86/xen/page.h
@@ -25,6 +25,11 @@
 #define INVALID_P2M_ENTRY      (~0UL)
 #define FOREIGN_FRAME_BIT      (1UL<<31)
 #define FOREIGN_FRAME(m)       ((m) | FOREIGN_FRAME_BIT)
+
+/* Maximum amount of memory we can handle in a domain in pages */
+#define MAX_DOMAIN_PAGES                                               \
+    ((unsigned long)((u64)CONFIG_XEN_MAX_DOMAIN_MEMORY * 1024 * 1024 * 1024 / 
PAGE_SIZE))
+
 
 extern unsigned long get_phys_to_machine(unsigned long pfn);
 extern void set_phys_to_machine(unsigned long pfn, unsigned long mfn);



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