Re: [PATCH 05/12] libxenguest: complete loops in xc_map_domain_meminfo()

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 25/06/2021 14:19, Jan Beulich wrote:
> minfo->p2m_size may have more than 31 significant bits. Change the
> induction variable to unsigned long, and (largely for signed-ness
> consistency) a helper variable to unsigned int.
>
> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
>
> --- a/tools/libs/guest/xg_domain.c
> +++ b/tools/libs/guest/xg_domain.c
> @@ -40,7 +40,7 @@ int xc_map_domain_meminfo(xc_interface *
>      xc_dominfo_t info;
>      shared_info_any_t *live_shinfo;
>      xen_capabilities_info_t xen_caps = "";
> -    int i;
> +    unsigned long i;
>  
>      /* Only be initialized once */
>      if ( minfo->pfn_type || minfo->p2m_table )
> @@ -116,12 +116,12 @@ int xc_map_domain_meminfo(xc_interface *
>      /* Retrieve PFN types in batches */
>      for ( i = 0; i < minfo->p2m_size ; i+=1024 )
>      {
> -        int count = ((minfo->p2m_size - i ) > 1024 ) ?
> -                        1024: (minfo->p2m_size - i);
> +        unsigned int count = ((minfo->p2m_size - i) > 1024) ?
> +                             1024 : (minfo->p2m_size - i);

min().

Otherwise, Acked-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>

This whole infrastructure is almost abandoned, and broken.  Its used by
xen-mfndump (debugging only) and xen-hptool mem-offline.

The mem-offline functionally cannot possibly work usefully.  It is PV
only, despite not having an HVM check, and in particular reads the dead
page in an attempt to restore the contents elsewhere.  There is also no
thought given to writes from outside sources, such as DMA from
passthrough or a different dom0 foreign mapping.

This is perhaps ok as an academic demonstration of "can I shuffle memory
behind an alive VM in ideal circumstances", but will be killed by the
dom0 kernel if you ever try running it to resolve a real memory error on
a VM, because there is no possibility of recovering the data.

The mem-offline functionality needs deleting.  It isn't production
ready, and can't credibly be made so.

~Andrew