Re: [PATCHv5 3/3] vhost_net: a kernel-level virtio server

[Michael S. Tsirkin]

On Wed, Sep 16, 2009 at 04:57:42PM +0200, Arnd Bergmann wrote:
> On Tuesday 15 September 2009, Michael S. Tsirkin wrote:
> > Userspace in x86 maps a PCI region, uses it for communication with ppc?
> 
> This might have portability issues. On x86 it should work, but if the
> host is powerpc or similar, you cannot reliably access PCI I/O memory
> through copy_tofrom_user but have to use memcpy_toio/fromio or readl/writel
> calls, which don't work on user pointers.
> 
> Specifically on powerpc, copy_from_user cannot access unaligned buffers
> if they are on an I/O mapping.
> 
> 	Arnd <><

We are talking about doing this in userspace, not in kernel.

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