Re: [Xen-devel] [PATCH] xen/x86: Fix errors arising from c/s dab76ff

[George Dunlap <george.dunlap@xxxxxxxxxx>]

On 12/02/16 14:59, Andrew Cooper wrote:
> Coverity correctly identifies that the changes in mtrr_attrib_to_str()
> introduce dead code.  strings[] is a 2d array, rather than an array of
> strings, which means that strings[x] will never be a NULL pointer.
> 
> Adjust the check to compenstate, by looking for a NUL in strings[x][0]
> instead.
> 
> Curiously, Coverity did not notice the same error with memory_type_to_str().
> There was also a further error; the strings were not NULL terminated, which
> made the return type of memory_type_to_str() erronious.
> 
> Bump the 2D array to 3 characters, so the strings retain their NUL characters,
> and introduce an ASSERT() as requested on one thread of the original patch.
> 
> Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>

What about something like this instead?  (Ported to be on top of this
patch, since it's already been committed.)

 -George

[PATCH] xen/p2m: Make dump table printing less clever

Rather than detecting whether to print out the numerical value of the
memory type based on whether
the second byte of the stringified value is a null character, just
always print out both.

Signed-off-by: George Dunlap <george.dunlap@xxxxxxxxxx>
---
CC: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
CC: Jan Beulich <jbeulich@xxxxxxxx>
CC: Tim Deegan <tim@xxxxxxx>
---
 xen/arch/x86/mm/p2m-ept.c | 9 ++++-----
 1 file changed, 4 insertions(+), 5 deletions(-)

diff --git a/xen/arch/x86/mm/p2m-ept.c b/xen/arch/x86/mm/p2m-ept.c
index 3cb6868..be528e7 100644
--- a/xen/arch/x86/mm/p2m-ept.c
+++ b/xen/arch/x86/mm/p2m-ept.c
@@ -1204,7 +1204,7 @@ void ept_p2m_uninit(struct p2m_domain *p2m)

 static const char *memory_type_to_str(unsigned int x)
 {
-    static const char memory_types[8][3] = {
+    static const char *memory_types[8] = {
         [MTRR_TYPE_UNCACHABLE]     = "UC",
         [MTRR_TYPE_WRCOMB]         = "WC",
         [MTRR_TYPE_WRTHROUGH]      = "WT",
@@ -1262,14 +1262,13 @@ static void ept_dump_p2m_table(unsigned char key)
                 if ( ept_entry->sa_p2mt == p2m_populate_on_demand )
                     printk("gfn: %13lx order: %2d PoD\n", gfn, order);
                 else
-                    printk("gfn: %13lx order: %2d mfn: %13lx %c%c%c
%c%c%c\n",
+                    printk("gfn: %13lx order: %2d mfn: %13lx %c%c%c
%s(%d)%c\n",
                            gfn, order, ept_entry->mfn + 0UL,
                            ept_entry->r ? 'r' : ' ',
                            ept_entry->w ? 'w' : ' ',
                            ept_entry->x ? 'x' : ' ',
-                           memory_type_to_str(ept_entry->emt)[0],
-                           memory_type_to_str(ept_entry->emt)[1]
-                           ?: ept_entry->emt + '0',
+                           memory_type_to_str(ept_entry->emt),
+                           ept_entry->emt,
                            c ?: ept_entry->ipat ? '!' : ' ');

                 if ( !(record_counter++ % 100) )
-- 
2.1.4

Attachment: 0001-xen-p2m-Make-dump-table-printing-less-clever.patch
Description: Text Data

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