Re: hypercalls with 64-bit results

[Juergen Gross <jgross@xxxxxxxx>]

On 16.06.21 18:04, Jan Beulich wrote:
> All,
>
> several years back do_memory_op() in libxc was changed to have "long"
> return type. This is because some of the sub-ops return potentially
> large values as the hypercall return value (i.e. not in an argument
> structure field). This change, however, didn't have the intended
> effect from all I can tell, which apparently manifests in the present
> two remaining ovmf failures in the staging osstest flights. Anthony
> tells me that ovmf as of not very long ago puts the shared info page
> at a really high address, thus making the p2m of the guest very large.
> Its size gets returned by XENMEM_maximum_gpfn, as function return
> value.
>
> Since hypercalls from the tool stack are based on ioctl(), and since
> ioctl() has a return type of "int", I'm afraid there's no way we can
> deal with this by adjusting function return types in the libraries.
> Instead we appear to need either a new privcmd ioctl or new XENMEM_*
> subops (for those cases where potentially large values get returned).
I think we can just use a multicall in libxc to wrap the affected
operations.


Juergen

Attachment: OpenPGP_0xB0DE9DD628BF132F.asc
Description: OpenPGP public key

Attachment: OpenPGP_signature
Description: OpenPGP digital signature