[Xen-devel] [PATCH v2] libxc: remove stale error check for domain size in xc_sr_save_x86_hvm.c

[Juergen Gross <jgross@xxxxxxxx>]

Long ago domains to be saved were limited to 1TB size due to the
migration stream v1 limitations which used a 32 bit value for the
PFN and the frame type (4 bits) leaving only 28 bits for the PFN.

Migration stream V2 uses a 64 bit value for this purpose, so there
is no need to refuse saving (or migrating) domains larger than 1 TB.

For 32 bit toolstacks there is still a size limit, as domains larger
than about 1TB will lead to an exhausted virtual address space of the
saving process. So keep the test for 32 bit, but don't base it on the
page type macros. As a migration could lead to the situation where a
32 bit toolstack would have to handle such a large domain (in case the
sending side is 64 bit) the same test should be added for restoring a
domain.

Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
---
I know we have code freeze. Nevertheless I'd like to request an
exception and get this into 4.10, as the impact of the patch is
very local and of low risk.

V2:
- keep test for 32 bit toolstack (Andrew Cooper)
- test against size value instead of not page type mask
- add related test on the receive side, too
---
 tools/libxc/xc_sr_restore_x86_hvm.c | 9 +++++++++
 tools/libxc/xc_sr_save_x86_hvm.c    | 5 ++++-
 2 files changed, 13 insertions(+), 1 deletion(-)

diff --git a/tools/libxc/xc_sr_restore_x86_hvm.c 
b/tools/libxc/xc_sr_restore_x86_hvm.c
index 1dca85354a..227c48553e 100644
--- a/tools/libxc/xc_sr_restore_x86_hvm.c
+++ b/tools/libxc/xc_sr_restore_x86_hvm.c
@@ -148,6 +148,15 @@ static int x86_hvm_setup(struct xc_sr_context *ctx)
               ctx->restore.guest_page_size);
         return -1;
     }
+#ifdef __i386__
+    /* Very large domains (> 1TB) will exhaust virtual address space. */
+    if ( ctx->restore.p2m_size > 0x0fffffff )
+    {
+        errno = E2BIG;
+        PERROR("Cannot restore this big a guest");
+        return -1;
+    }
+#endif
 
     return 0;
 }
diff --git a/tools/libxc/xc_sr_save_x86_hvm.c b/tools/libxc/xc_sr_save_x86_hvm.c
index e17bb59146..97a8c49807 100644
--- a/tools/libxc/xc_sr_save_x86_hvm.c
+++ b/tools/libxc/xc_sr_save_x86_hvm.c
@@ -148,12 +148,15 @@ static int x86_hvm_setup(struct xc_sr_context *ctx)
         PERROR("Unable to obtain the guest p2m size");
         return -1;
     }
-    if ( nr_pfns > ~XEN_DOMCTL_PFINFO_LTAB_MASK )
+#ifdef __i386__
+    /* Very large domains (> 1TB) will exhaust virtual address space. */
+    if ( nr_pfns > 0x0fffffff )
     {
         errno = E2BIG;
         PERROR("Cannot save this big a guest");
         return -1;
     }
+#endif
 
     ctx->save.p2m_size = nr_pfns;
 
-- 
2.12.3


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