Re: Problem about dump-core

[Wen Congyang <wency@cn.fujitsu.com>]

On 09/17/2014 09:11 AM, Ian Campbell wrote:
> On Wed, 2014-09-17 at 08:50 +0800, Wen Congyang wrote:
> 
>> Yes, we can check it more earlier. If the 4 error bits are set, is it a valid
>> mfn?
> 
> It doesn't really matter, since valid or not you can't pass such an mfn
> to this interface because of the error handling behaviour.

No, the user may pass more than one mfn, and part of them are ~0UL:
==============================================
    for ( i = 0; i < j; i++ )
    {
        unsigned long pfn, pagetype;
        pfn      = pagebuf->pfn_types[i + curbatch] & ~XEN_DOMCTL_PFINFO_LTAB_MASK;
        pagetype = pagebuf->pfn_types[i + curbatch] &  XEN_DOMCTL_PFINFO_LTAB_MASK;

        if ( pagetype != XEN_DOMCTL_PFINFO_XTAB
             && ctx->p2m[pfn] == (INVALID_P2M_ENTRY-1) )
        {
            /* We just allocated a new mfn above; update p2m */
            ctx->p2m[pfn] = ctx->p2m_batch[nr_mfns++]; 
            ctx->nr_pfns++; 
        }

        /* setup region_mfn[] for batch map, if necessary.
         * For HVM guests, this interface takes PFNs, not MFNs */
        if ( pagetype == XEN_DOMCTL_PFINFO_XTAB
             || pagetype == XEN_DOMCTL_PFINFO_XALLOC )
            region_mfn[i] = ~0UL; /* map will fail but we don't care */
        else
            region_mfn[i] = ctx->hvm ? pfn : ctx->p2m[pfn];
    }

    /* Map relevant mfns */
    pfn_err = calloc(j, sizeof(*pfn_err));
    if ( pfn_err == NULL )
    {
        PERROR("allocation for pfn_err failed");
        return -1;
    }
    region_base = xc_map_foreign_bulk(
        xch, dom, PROT_WRITE, region_mfn, pfn_err, j);
==============================================
The above codes are the function apply_batch(). In this case, we cannot
return NULL.

I think we should check the mfn, and if it is large mfn, and some error bits
are set, pass ~0UL to ioctl(), and mark this mfn is mapped failed in err[].

Thanks
Wen Congyang

> 
> Ian.
> 
> .
>