lkml.org 
[lkml]   [2000]   [Nov]   [27]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: How to transfer memory from PCI memory directly to user space safely and portable?
Philipp Rumpf wrote:
>
> On Mon, Nov 27, 2000 at 10:36:34AM -0800, H. Peter Anvin wrote:
> > Followup to: <20001126151120.V2272@parcelfarce.linux.theplanet.co.uk>
> > By author: Philipp Rumpf <prumpf@parcelfarce.linux.theplanet.co.uk>
> > In newsgroup: linux.dev.kernel
> > >
> > > I hope count isn't provided by userspace here ?
> > >
> > > > 1. What happens if the user space memory is swapped to disk? Will
> > > > verify_area() make sure that the memory is in physical RAM when it returns,
> > > > or will it return -EFAULT, or will something even worse happen?
> > >
> > > On i386, you'll sleep implicitly waiting for the page fault to be handled; in
> > > the generic case, anything could happen.
> > >
> >
> > That doesn't sound right. I would expect it to wait for the page to
> > be brought in on any and all architectures, otherwise it seems rather
> > impossible to write portable Linux kernel code.
>
> The code in question was
> memcpy_fromio(user_space_dst, iobase, count);
>
> Assuming user_space_dst is a userspace pointer, what I said is true; on some
> architectures we will be dereferencing random pointers in kernel space, and
> we won't get -EFAULT right on any architecture.
>
> Or did I miss something ?
>

Yes, the post you responded to was talking about verify_area() [which is,
admittedly, obsolete.]

-hpa

--
<hpa@transmeta.com> at work, <hpa@zytor.com> in private!
"Unix gives you enough rope to shoot yourself in the foot."
http://www.zytor.com/~hpa/puzzle.txt
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
Please read the FAQ at http://www.tux.org/lkml/

\
 
 \ /
  Last update: 2005-03-22 12:47    [W:0.049 / U:0.256 seconds]
©2003-2018 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site