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

On Wed, Aug 30, 2017 at 07:45:17PM +1000, Paul Mackerras wrote:

On Tue, Aug 29, 2017 at 07:18:01PM -0300, Jose Ricardo Ziviani wrote:

quoted

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.

Hello Paul,

My bad, actually it works. I was mmap'ping an address that doesn't allow 16-byte writing access. After mmap'ping a higher address (of the same device) I was able to perform 16-byte read/write.

== before stvx ==

  (gdb) info registers vr0
  vr0  {uint128 = 0x000000001234567800000000abcdef09, ...}

  (gdb) info registers r9
  r9 0x3fffb7c90010

  (gdb) x /4wx 0x3fffb7c90010
  0x3fffb7c90010: 0x00000000 0x00000000 0x00000000 0x00000000

  (gdb) info registers r28
  r28 0x0 

stvx    v0,r28,r9

== after stvx ==

  (gdb) x /4wx 0x3fffb7c90010
  0x3fffb7c90010: 0x12345678 0x00000000 0xabcdef09 0x00000000

== before lvx ==

  (gdb) info registers vr10
  vr10 {uint128 = 0x00000000000000000000000000000000,...}

lvx     v10,r28,r9

== after lvx ==

  (gdb) info registers vr10
  vr10 {uint128 = 0x000000001234567800000000abcdef09,...}

If you think it's ok I'll submit this patch without the RFC.

Thank you very much!

Ziviani