Re: [PATCH RFC] powerpc: Implements MMIO emulation for lvx/stvx instructions

[Paul Mackerras <paulus@ozlabs.org>]

On Tue, Aug 29, 2017 at 07:18:01PM -0300, Jose Ricardo Ziviani wrote:
> Hello!
> 
> This patch implements MMIO emulation for two instructions: lvx and stvx. I started to implement other instructions but I'd like to have this reviewed beforehand because this is my first patch here and I'll certainly have some rework/fixes :-).
> 
> Note: stvx is only storing 8 bytes, for some reason the code "vcpu->arch.paddr_accessed += run->mmio.len;", which adds the 8-byte offset after the first write is not making any difference (interesting that it works for load operations). I'm still investigating it but any idea about it will be appreciated.

The run structure is mmapped by userspace (i.e. QEMU) and can be
written by userspace between the first and the second exits to
userspace (you have to do two exits to userspace because you can only
transfer 8 bytes on each exit).  It's possible that userspace might be
clearing run->mmio.len.  In general it's better not to rely on
anything in *run (except of course the mmio_data for a MMIO read) when
we come in from userspace to the kernel.

Paul.