Re: [PATCH v2 4/9] xen/x86: Use ASSERT instead of VIRTUAL_BUG_ON for phys_to_nid

[Jan Beulich <jbeulich@xxxxxxxx>]

On 08.07.2022 16:54, Wei Chen wrote:
> VIRTUAL_BUG_ON is an empty macro used in phys_to_nid. This
> results in two lines of error-checking code in phys_to_nid
> that is not actually working and causing two compilation
> errors:
> 1. error: "MAX_NUMNODES" undeclared (first use in this function).
>    This is because in the common header file, "MAX_NUMNODES" is
>    defined after the common header file includes the ARCH header
>    file, where phys_to_nid has attempted to use "MAX_NUMNODES".
>    This error was resolved after we moved the phys_to_nid from
>    x86 ARCH header file to common header file.
> 2. error: wrong type argument to unary exclamation mark.
>    This is because, the error-checking code contains !node_data[nid].
>    But node_data is a data structure variable, it's not a pointer.
> 
> So, in this patch, we use ASSERT instead of VIRTUAL_BUG_ON to
> enable the two lines of error-checking code. And fix the left
> compilation errors by replacing !node_data[nid] to
> !node_data[nid].node_spanned_pages. Although NUMA allows one node
> can only have CPUs but without any memory. And node with 0 bytes
> of memory might have an entry in memnodemap[] theoretically. But
> that doesn't mean phys_to_nid can find any valid address from a
> node with 0 bytes memory.
> 
> Signed-off-by: Wei Chen <wei.chen@xxxxxxx>
> Tested-by: Jiamei Xie <jiamei.xie@xxxxxxx>
> ---
> v1 -> v2:
> 1. Move from part#1 to part#2. (Comment from NUMA part1 series)
> 2. Refine the justification of using
>    !node_data[nid].node_spanned_pages. (From NUMA part1 series)
> 3. Use ASSERT to replace VIRTUAL_BUG_ON in phys_to_nid.
> 4. Adjust the conditional express for ASSERT.
> 5. Move MAX_NUMNODES from xen/numa.h to asm/numa.h for x86.
> 6. Use conditional macro to gate MAX_NUMNODES for other architectures.

The change looks okay, but can you please clarify what these last two
points describe? They don't seem to match any change ...

> --- a/xen/include/xen/numa.h
> +++ b/xen/include/xen/numa.h
> @@ -36,8 +36,6 @@ struct node {
>  extern int compute_hash_shift(struct node *nodes, int numnodes,
>                                nodeid_t *nodeids);
>  
> -#define VIRTUAL_BUG_ON(x)
> -
>  /* Enumerations for NUMA status. */
>  enum numa_mode {
>      numa_on = 0,
> @@ -77,9 +75,9 @@ extern struct node_data node_data[];
>  static inline __attribute__((pure)) nodeid_t phys_to_nid(paddr_t addr)
>  {
>      nodeid_t nid;
> -    VIRTUAL_BUG_ON((paddr_to_pdx(addr) >> memnode_shift) >= memnodemapsize);
> +    ASSERT((paddr_to_pdx(addr) >> memnode_shift) < memnodemapsize);
>      nid = memnodemap[paddr_to_pdx(addr) >> memnode_shift];
> -    VIRTUAL_BUG_ON(nid >= MAX_NUMNODES || !node_data[nid]);
> +    ASSERT(nid < MAX_NUMNODES && node_data[nid].node_spanned_pages);
>      return nid;
>  }
>  

... in the entire patch.

Jan