[Xen-devel] [PATCH v2 19/22] libxc/xen: introduce HVM_PARAM_FIRST_FREE_PFN

[Roger Pau Monne <roger.pau@xxxxxxxxxx>]

This HVM parameter returns the first free pfn after all the special pages.
It can be used by guests to figure out the first free memory address after
the kernel, ramdisk and special pages. This is interesting for compatibility
reasons in case more special pages are later added, older guests can still
use this parameter to figure out the first free address, ignoring newly
added special pages.

Signed-off-by: Roger Pau Monnà <roger.pau@xxxxxxxxxx>
Cc: Ian Jackson <ian.jackson@xxxxxxxxxxxxx>
Cc: Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>
Cc: Ian Campbell <ian.campbell@xxxxxxxxxx>
Cc: Wei Liu <wei.liu2@xxxxxxxxxx>
Cc: Jan Beulich <jbeulich@xxxxxxxx>
Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
---
 tools/libxc/xc_dom_x86.c        | 2 ++
 xen/arch/x86/hvm/hvm.c          | 1 +
 xen/include/public/hvm/params.h | 5 ++++-
 3 files changed, 7 insertions(+), 1 deletion(-)

diff --git a/tools/libxc/xc_dom_x86.c b/tools/libxc/xc_dom_x86.c
index 41ff7a4..74c3819 100644
--- a/tools/libxc/xc_dom_x86.c
+++ b/tools/libxc/xc_dom_x86.c
@@ -573,6 +573,8 @@ static int alloc_magic_pages_hvm(struct xc_dom_image *dom)
                      special_pfn(SPECIALPAGE_ACCESS, dom));
     xc_hvm_param_set(xch, domid, HVM_PARAM_SHARING_RING_PFN,
                      special_pfn(SPECIALPAGE_SHARING, dom));
+    xc_hvm_param_set(xch, domid, HVM_PARAM_FIRST_FREE_PFN,
+                     special_pfn(NR_SPECIAL_PAGES, dom));
 
     if ( dom->cmdline )
     {
diff --git a/xen/arch/x86/hvm/hvm.c b/xen/arch/x86/hvm/hvm.c
index 945f42e..b7b1300 100644
--- a/xen/arch/x86/hvm/hvm.c
+++ b/xen/arch/x86/hvm/hvm.c
@@ -5901,6 +5901,7 @@ static int hvm_allow_get_param(struct domain *d,
     case HVM_PARAM_CONSOLE_PFN:
     case HVM_PARAM_CONSOLE_EVTCHN:
     case HVM_PARAM_CMDLINE_PFN:
+    case HVM_PARAM_FIRST_FREE_PFN:
         break;
     /*
      * The following parameters must not be read by the guest
diff --git a/xen/include/public/hvm/params.h b/xen/include/public/hvm/params.h
index b7f8839..47e38a8 100644
--- a/xen/include/public/hvm/params.h
+++ b/xen/include/public/hvm/params.h
@@ -190,6 +190,9 @@
 /* PFN of the command line. */
 #define HVM_PARAM_CMDLINE_PFN 35
 
-#define HVM_NR_PARAMS          36
+/* First free PFN after the special pages. */
+#define HVM_PARAM_FIRST_FREE_PFN 36
+
+#define HVM_NR_PARAMS          37
 
 #endif /* __XEN_PUBLIC_HVM_PARAMS_H__ */
-- 
1.9.5 (Apple Git-50.3)


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