Re: [PATCH 00/18] uaccess: fix sparse warning on get_user for bitwise types

From: LF.Tan
Date: Mon Dec 15 2014 - 05:03:19 EST

On Mon, Dec 15, 2014 at 12:51 AM, Michael S. Tsirkin <mst@xxxxxxxxxx> wrote:
> At the moment, if p and x are both tagged as bitwise types,
> get_user(x, p) produces a sparse warning on many architectures.
> This is because *p on these architectures is loaded into long
> (typically using asm), then cast back to typeof(*p).
> When typeof(*p) is a bitwise type (which is uncommon), such a cast needs
> __force, otherwise sparse produces a warning.
> Some architectures already have the __force tag, add it
> where it's missing.
> Specificlly, vhost wants to read bitwise types from userspace using get_user.
> At the moment this triggers sparse errors, since the value is passed through an
> integer.
> For now, I worked around this by converting vhost code to access_ok +
> __get_user, but that's not robust, I'd like to switch to get_user for 3.19.
> I tested this on x86 only so far. Since it's just adding __force, should be
> trivially safe everywhere?
> Please review, and consider for 3.19.
> Who can merge this? Arnd?
Hi Michael

FYI, there is new arch (arch/nios2) in 3.19. Is your patchset include
the fix for it?

Ley Foon
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