x86: improve output resulting from sending '0' over serial

While the original logic already implied that the kernel part of the
guest's address space is identical on all vCPU-s (i.e. for all guest
processes), it didn't fully leverage the potential here: As long as
the top page table currently active is owned by the subject domain
(currently only Dom0), the stack dump can be done without extra
effort.

For x86-64, additionally add page table traversal so that the stack
can be dumped in all cases (unless it's invalid or user space).

I left the 32-bit variant of do_page_walk() unimplemented for the
moment as I couldn't convince myself using map_domain_page() there is
a good idea, and didn't want to introduce new fixmap entries either.

Signed-off-by: Jan Beulich <jbeulich@novell.com>

1 files changed, 6 insertions, 3 deletions

diff --git a/xen/include/asm-x86/x86_64/uaccess.h b/xen/include/asm-x86/x86_64/uaccess.h
index 2080be86b1..4433fd0b69 100644
--- a/xen/include/asm-x86/x86_64/uaccess.h
+++ b/xen/include/asm-x86/x86_64/uaccess.h
@@ -27,11 +27,14 @@ DECLARE_PER_CPU(char, compat_arg_xlat[COMPAT_ARG_XLAT_SIZE]);
 #define array_access_ok(addr, count, size) \
     (access_ok(addr, (count)*(size)))
 
-#define __compat_addr_ok(addr) \
-    ((unsigned long)(addr) < HYPERVISOR_COMPAT_VIRT_START(current->domain))
+#define __compat_addr_ok(d, addr) \
+    ((unsigned long)(addr) < HYPERVISOR_COMPAT_VIRT_START(d))
+
+#define __compat_access_ok(d, addr, size) \
+    __compat_addr_ok(d, (unsigned long)(addr) + ((size) ? (size) - 1 : 0))
 
 #define compat_access_ok(addr, size) \
-    __compat_addr_ok((unsigned long)(addr) + ((size) ? (size) - 1 : 0))
+    __compat_access_ok(current->domain, addr, size)
 
 #define compat_array_access_ok(addr,count,size) \
     (likely((count) < (~0U / (size))) && \