[Xen-devel] [PATCH v9 01/10] xen: add function for obtaining highest possible memory address

[Juergen Gross <jgross@xxxxxxxx>]

Add a function for obtaining the highest possible physical memory
address of the system. This value is influenced by:

- hypervisor configuration (CONFIG_BIGMEM)
- processor capability (max. addressable physical memory)
- memory map at boot time
- memory hotplug capability

Add this value to xen_sysctl_physinfo in order to enable dom0 to do a
proper sizing of grant frame limits of guests.

Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
---
V9:
- merge patch with following one (Jan Beulich)
- bump sysctl interface version (Julien Grall)
- drop thin common shim of get_upper_mfn_bound() (Jan Beulich)
- let get_upper_mfn_bound() return the highest MFN, not the one
  following it (Jan Beulich)
---
 xen/arch/arm/mm.c           |  6 ++++++
 xen/arch/x86/mm.c           | 11 +++++++++++
 xen/common/sysctl.c         |  1 +
 xen/include/public/sysctl.h |  4 +++-
 xen/include/xen/mm.h        |  3 +++
 5 files changed, 24 insertions(+), 1 deletion(-)

diff --git a/xen/arch/arm/mm.c b/xen/arch/arm/mm.c
index f3834b3dab..9a37f29ce6 100644
--- a/xen/arch/arm/mm.c
+++ b/xen/arch/arm/mm.c
@@ -1472,6 +1472,12 @@ void clear_and_clean_page(struct page_info *page)
     unmap_domain_page(p);
 }
 
+unsigned long get_upper_mfn_bound(void)
+{
+    /* No memory hotplug yet, so current memory limit is the final one. */
+    return max_page - 1;
+}
+
 /*
  * Local variables:
  * mode: C
diff --git a/xen/arch/x86/mm.c b/xen/arch/x86/mm.c
index 67f583e3a7..7af371d499 100644
--- a/xen/arch/x86/mm.c
+++ b/xen/arch/x86/mm.c
@@ -6312,6 +6312,17 @@ int pv_ro_page_fault(unsigned long addr, struct 
cpu_user_regs *regs)
     return 0;
 }
 
+unsigned long get_upper_mfn_bound(void)
+{
+    unsigned long max_mfn;
+
+    max_mfn = mem_hotplug ? PFN_DOWN(mem_hotplug) : max_page;
+#ifndef CONFIG_BIGMEM
+    max_mfn = min(max_mfn, 1UL << 32);
+#endif
+    return min(max_mfn, 1UL << (paddr_bits - PAGE_SHIFT)) - 1;
+}
+
 /*
  * Local variables:
  * mode: C
diff --git a/xen/common/sysctl.c b/xen/common/sysctl.c
index 3480f582fa..08198b7150 100644
--- a/xen/common/sysctl.c
+++ b/xen/common/sysctl.c
@@ -266,6 +266,7 @@ long do_sysctl(XEN_GUEST_HANDLE_PARAM(xen_sysctl_t) 
u_sysctl)
         get_outstanding_claims(&pi->free_pages, &pi->outstanding_pages);
         pi->scrub_pages = 0;
         pi->cpu_khz = cpu_khz;
+        pi->max_mfn = get_upper_mfn_bound();
         arch_do_physinfo(pi);
 
         if ( copy_to_guest(u_sysctl, op, 1) )
diff --git a/xen/include/public/sysctl.h b/xen/include/public/sysctl.h
index 4d32a87cca..4315881c12 100644
--- a/xen/include/public/sysctl.h
+++ b/xen/include/public/sysctl.h
@@ -36,7 +36,7 @@
 #include "physdev.h"
 #include "tmem.h"
 
-#define XEN_SYSCTL_INTERFACE_VERSION 0x0000000F
+#define XEN_SYSCTL_INTERFACE_VERSION 0x00000010
 
 /*
  * Read console content from Xen buffer ring.
@@ -104,6 +104,8 @@ struct xen_sysctl_physinfo {
 
     /* XEN_SYSCTL_PHYSCAP_??? */
     uint32_t capabilities;
+
+    uint64_t max_mfn;     /* Largest possible MFN on this host */
 };
 
 /*
diff --git a/xen/include/xen/mm.h b/xen/include/xen/mm.h
index f8b6177c32..e813c07b22 100644
--- a/xen/include/xen/mm.h
+++ b/xen/include/xen/mm.h
@@ -599,6 +599,9 @@ int prepare_ring_for_helper(struct domain *d, unsigned long 
gmfn,
                             struct page_info **_page, void **_va);
 void destroy_ring_for_helper(void **_va, struct page_info *page);
 
+/* Return the upper bound of MFNs, including hotplug memory. */
+unsigned long get_upper_mfn_bound(void);
+
 #include <asm/flushtlb.h>
 
 static inline void accumulate_tlbflush(bool *need_tlbflush,
-- 
2.12.3


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