Re: [Xen-devel] [PATCH] xen/tmem: Fix uses of unmatched __map_domain_page()

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 03/12/13 21:48, Andrew Cooper wrote:
> On 03/12/2013 21:00, Konrad Rzeszutek Wilk wrote:
>> On Wed, Nov 27, 2013 at 02:55:04PM +0000, Andrew Cooper wrote:
>>> I noticed this while looking through tmem_xen.h with regards to the
>>> recently-discovered Coverity issues.  As the issue was not noticed or
>>> referenced in Bob's cleanup series, I figured it was fair game, given its
>>> severity.
>>>
>>> __map_domain_page() *must* be matched with an unmap_domain_page().  These 
>>> five
>>> static inline functions each map a page (or two), then throw away the 
>>> context
>>> needed to unmap it.
>> I was trying to figure out how it worked before. I had been running with
>> tze enabled (I hope!) and I did not trigger any mapcache exhaustion.
>>
>> Ah wait, I had been on my nighly regression system  - which has some
>> guests that use tmem but they don't create any load fast enough.
>>
>> Let me queue this up and test it. Bob, would appreciate you testing
>> it too - just in case.
>>
>> Thanks!
> Depends which version of Xen.  Before Jan did the 16TB support during
> 4.3, __map_domain_page() was effectively a noop on 64bit, being
> mfn_to_virt().
>
> ~Andrew

After the most recent coverity run with the map_domain_page() modelling,
CIDs 1135373 thru 1135379 now apply to the fixes in this patch.

~Andrew

>
>>> Each of the changes are limited to their respective functions.  In two 
>>> cases,
>>> this involved replacing a large amount of pointer arithmetic with memcpy()
>>> (all callers were relying on memcpy() semantics of positive/negative returns
>>> rather than specifically -1/+1). A third case had its pointer arithmetic
>>> entirely replaced with memcpy().
>>>
>>> In addition, remove redundant casts of void pointers and assertions.
>>>
>>> Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
>>> CC: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
>>> CC: Bob Liu <bob.liu@xxxxxxxxxx>
>>> CC: Keir Fraser <keir@xxxxxxx>
>>> CC: Jan Beulich <JBeulich@xxxxxxxx>
>>>
>>> ---
>>> These changes have been compile tested, but not functionally tested.
>>> ---
>>>  xen/include/xen/tmem_xen.h |   78 
>>> +++++++++++++++++++++++---------------------
>>>  1 file changed, 40 insertions(+), 38 deletions(-)
>>>
>>> diff --git a/xen/include/xen/tmem_xen.h b/xen/include/xen/tmem_xen.h
>>> index b26c6fa..a0d11aa 100644
>>> --- a/xen/include/xen/tmem_xen.h
>>> +++ b/xen/include/xen/tmem_xen.h
>>> @@ -228,26 +228,24 @@ static inline bool_t tmem_current_is_privileged(void)
>>>  
>>>  static inline uint8_t tmem_get_first_byte(struct page_info *pfp)
>>>  {
>>> -    void *p = __map_domain_page(pfp);
>>> +    const uint8_t *p =__map_domain_page(pfp);
>>> +    uint8_t byte = p[0];
>>>  
>>> -    return (uint8_t)(*(char *)p);
>>> +    unmap_domain_page(p);
>>> +
>>> +    return byte;
>>>  }
>>>  
>>>  static inline int tmem_page_cmp(struct page_info *pfp1, struct page_info 
>>> *pfp2)
>>>  {
>>> -    const uint64_t *p1 = (uint64_t *)__map_domain_page(pfp1);
>>> -    const uint64_t *p2 = (uint64_t *)__map_domain_page(pfp2);
>>> -    int i;
>>> -
>>> -    // FIXME: code in assembly?
>>> -ASSERT(p1 != NULL);
>>> -ASSERT(p2 != NULL);
>>> -    for ( i = PAGE_SIZE/sizeof(uint64_t); i && *p1 == *p2; i--, p1++, p2++ 
>>> );
>>> -    if ( !i )
>>> -        return 0;
>>> -    if ( *p1 < *p2 )
>>> -        return -1;
>>> -    return 1;
>>> +    const uint64_t *p1 = __map_domain_page(pfp1);
>>> +    const uint64_t *p2 = __map_domain_page(pfp2);
>>> +    int rc = memcmp(p1, p2, PAGE_SIZE);
>>> +
>>> +    unmap_domain_page(p2);
>>> +    unmap_domain_page(p1);
>>> +
>>> +    return rc;
>>>  }
>>>  
>>>  static inline int tmem_pcd_cmp(void *va1, pagesize_t len1, void *va2, 
>>> pagesize_t len2)
>>> @@ -271,54 +269,58 @@ static inline int tmem_pcd_cmp(void *va1, pagesize_t 
>>> len1, void *va2, pagesize_t
>>>      return 1;
>>>  }
>>>  
>>> -static inline int tmem_tze_pfp_cmp(struct page_info *pfp1, pagesize_t 
>>> pfp_len, void *tva, pagesize_t tze_len)
>>> +static inline int tmem_tze_pfp_cmp(struct page_info *pfp1, pagesize_t 
>>> pfp_len,
>>> +                                   void *tva, const pagesize_t tze_len)
>>>  {
>>> -    const uint64_t *p1 = (uint64_t *)__map_domain_page(pfp1);
>>> -    const uint64_t *p2;
>>> -    pagesize_t i;
>>> +    const uint64_t *p1 = __map_domain_page(pfp1);
>>> +    const uint64_t *p2 = tze_len == PAGE_SIZE ?
>>> +        __map_domain_page((struct page_info *)tva) : tva;
>>> +    int rc;
>>>  
>>> -    if ( tze_len == PAGE_SIZE )
>>> -       p2 = (uint64_t *)__map_domain_page((struct page_info *)tva);
>>> -    else
>>> -       p2 = (uint64_t *)tva;
>>>      ASSERT(pfp_len <= PAGE_SIZE);
>>>      ASSERT(!(pfp_len & (sizeof(uint64_t)-1)));
>>>      ASSERT(tze_len <= PAGE_SIZE);
>>>      ASSERT(!(tze_len & (sizeof(uint64_t)-1)));
>>>      if ( pfp_len < tze_len )
>>> -        return -1;
>>> -    if ( pfp_len > tze_len )
>>> -        return 1;
>>> -    ASSERT(pfp_len == tze_len);
>>> -    for ( i = tze_len/sizeof(uint64_t); i && *p1 == *p2; i--, p1++, p2++ );
>>> -    if ( !i )
>>> -        return 0;
>>> -    if ( *p1 < *p2 )
>>> -        return -1;
>>> -    return 1;
>>> +        rc = -1;
>>> +    else if ( pfp_len > tze_len )
>>> +        rc = 1;
>>> +    else
>>> +        rc = memcmp(p1, p2, tze_len);
>>> +
>>> +    if ( tze_len == PAGE_SIZE )
>>> +        unmap_domain_page(p2);
>>> +    unmap_domain_page(p1);
>>> +
>>> +    return rc;
>>>  }
>>>  
>>>  /* return the size of the data in the pfp, ignoring trailing zeroes and
>>>   * rounded up to the nearest multiple of 8 */
>>>  static inline pagesize_t tmem_tze_pfp_scan(struct page_info *pfp)
>>>  {
>>> -    const uint64_t *p = (uint64_t *)__map_domain_page(pfp);
>>> +    const uint64_t *const page = __map_domain_page(pfp);
>>> +    const uint64_t *p = page;
>>>      pagesize_t bytecount = PAGE_SIZE;
>>>      pagesize_t len = PAGE_SIZE/sizeof(uint64_t);
>>> +
>>>      p += len;
>>>      while ( len-- && !*--p )
>>>          bytecount -= sizeof(uint64_t);
>>> +
>>> +    unmap_domain_page(page);
>>> +
>>>      return bytecount;
>>>  }
>>>  
>>>  static inline void tmem_tze_copy_from_pfp(void *tva, struct page_info 
>>> *pfp, pagesize_t len)
>>>  {
>>> -    uint64_t *p1 = (uint64_t *)tva;
>>> -    const uint64_t *p2 = (uint64_t *)__map_domain_page(pfp);
>>> +    const uint64_t *p = __map_domain_page(pfp);
>>>  
>>> -    pagesize_t i;
>>>      ASSERT(!(len & (sizeof(uint64_t)-1)));
>>> -    for ( i = len/sizeof(uint64_t); i--; *p1++ = *p2++);
>>> +    memcpy(tva, p, len);
>>> +
>>> +    unmap_domain_page(p);
>>>  }
>>>  
>>>  /* these typedefs are in the public/tmem.h interface
>>> -- 
>>> 1.7.10.4
>>>
>
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