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

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

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.

> 
> 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.
> >
> 



_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxx
http://lists.xen.org/xen-devel