Re: [Xen-devel] ARM fixes for my improved privcmd patch.

[Mats Petersson <mats.petersson@xxxxxxxxxx>]

On 19/12/12 15:45, Ian Campbell wrote:
> On Wed, 2012-12-19 at 15:08 +0000, Mats Petersson wrote:
> > On 19/12/12 12:22, Ian Campbell wrote:
> > > On Wed, 2012-12-19 at 12:10 +0000, Mats Petersson wrote:
> > >
> > > > > > +                  only likely to return EFAULT or some other "things are very
> > > > > > +                  bad" error code, which the rest of the calling code won't
> > > > > > +                  be able to fix up. So we just exit with the error we got.
> > > > > It expect it is more important to accumulate the individual errors from
> > > > > remap_pte_fn into err_ptr.
> > > > Yes, but since that exits on error with EFAULT, the calling code won't
> > > > "accept" the errors, and thus the whole house of cards fall apart at
> > > > this point.
> > > >
> > > > There should probably be a task to fix this up properly, hence the
> > > > comment. But right now, any error besides ENOENT is "unacceptable" by
> > > > the callers of this code. If you want me to add this to the comment, I'm
> > > > happy to. But as long as remap_pte_fn returns EFAULT on error, nothing
> > > > will work after an error.
> > > Are you sure? privcmd.c has some special casing for ENOENT but it looks
> > > like it should just pass through other errors back to userspace.
> > >
> > > In any case surely this needs fixing?
> > >
> > > On the X86 side err_ptr is the result of the mmupdate hypercall which
> > > can already be other than ENOENT, including EFAULT, ESRCH etc.
> > Yes, but the ONLY error that is "acceptable" (as in, doesn't lead to the
> > calling code revoking the mapping and returning an error) is ENOENT.
> Hr, Probably the right thing is for map_foreign_page to propagate the
> result of XENMEM_add_to_physmap_range and for remap_pte_fn to store it
> in err_ptr. That -EFAULT thing just looks wrong to me.
Ok, so you want me to fix that up, I suppose? I mean, I just copied the 
behaviour that was already there - just massaged the code around a bit...
--
Mats
> > Or at least, that's how I believe it should SHOULD be - since only
> > ENOENT is a "success" error code, anything else pretty much means that
> > the operation requested didn't work properly. If you are aware of any
> > use-case where EFAULT, ESRCH or other error codes would still result in
> > a valid, usable memory mapping - I have a fair understanding of the xc_*
> > code, and although I may not know every piece of that code, I'm fairly
> > certainly that is the expected behaviour.
> >
> > --
> > Mats
> > > Ian.

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