On 18/06/2021 11:24, Jan Beulich wrote:
> Some sub-functions, XENMEM_maximum_gpfn in particular, can return values
> requiring more than 31 bits to represent. Hence we cannot issue the
> hypercall directly when the return value of ioctl() is used to propagate
> this value (note that this is not the case for the BSDs, and MiniOS
> already wraps all hypercalls in a multicall).
>
> Suggested-by: Jürgen Groß <jgr...@suse.com>
> Signed-off-by: Jan Beulich <jbeul...@suse.com>
>
> --- a/tools/libs/ctrl/xc_private.c
> +++ b/tools/libs/ctrl/xc_private.c
> @@ -337,8 +337,47 @@ long do_memory_op(xc_interface *xch, int
> goto out1;
> }
>
> - ret = xencall2(xch->xcall, __HYPERVISOR_memory_op,
> - cmd, HYPERCALL_BUFFER_AS_ARG(arg));
> +#if defined(__linux__) || defined(__sun__)
> + /*
> + * Some sub-ops return values which don't fit in "int". On platforms
> + * without a specific hypercall return value field in the privcmd
> + * interface structure, issue the request as a single-element multicall,
> + * to be able to capture the full return value.
> + */
> + if ( sizeof(long) > sizeof(int) )
This is very fragile. I spent a while coming up with
__builtin_types_compatible_p(
typeof(ioctl) *,
long (*)(int, unsigned long, ...));
(which does work if you change int for long), just to realise that this
won't actually help. I'm suck on trying to see whether
privcmd_hypercall_t has a result member.
> + {
> + multicall_entry_t multicall = {
> + .op = __HYPERVISOR_memory_op,
> + .args[0] = cmd,
> + .args[1] = HYPERCALL_BUFFER_AS_ARG(arg),
> + }, *call = &multicall;
> + DECLARE_HYPERCALL_BOUNCE(call, sizeof(*call),
> + XC_HYPERCALL_BUFFER_BOUNCE_BOTH);
> +
> + if ( xc_hypercall_bounce_pre(xch, call) )
> + {
> + PERROR("Could not bounce buffer for memory_op hypercall");
> + goto out1;
> + }
> +
> + ret = do_multicall_op(xch, HYPERCALL_BUFFER(call), 1);
> +
> + xc_hypercall_bounce_post(xch, call);
> +
> + if ( !ret )
> + {
> + ret = multicall.result;
> + if ( multicall.result > ~0xfffUL )
Wouldn't this be clearer as > -4095 ?
~Andrew
> + {
> + errno = -ret;
> + ret = -1;
> + }
> + }
> + }
> + else
> +#endif
> + ret = xencall2L(xch->xcall, __HYPERVISOR_memory_op,
> + cmd, HYPERCALL_BUFFER_AS_ARG(arg));
>
> xc_hypercall_bounce_post(xch, arg);
> out1:
>
>
