Re: [Qemu-devel] [PATCH v8 11/20] virtio: add endian-ambivalent support to VirtIODevice

[Greg Kurz <gkurz@linux.vnet.ibm.com>]

On Fri, 13 Jun 2014 14:41:30 +0200
Alexander Graf <agraf@suse.de> wrote:

> 
> On 13.06.14 14:14, Greg Kurz wrote:
> > On Fri, 13 Jun 2014 13:46:39 +0200
> > Alexander Graf <agraf@suse.de> wrote:
> >
> >> On 13.06.14 13:23, Greg Kurz wrote:
> >>> Some CPU families can dynamically change their endianness. This means we
> >>> can have little endian ppc or big endian arm guests for example. This has
> >>> an impact on legacy virtio data structures since they are target endian.
> >>> We hence introduce a new property to track the endianness of each virtio
> >>> device. It is reasonnably assumed that endianness won't change while the
> >>> device is in use : we hence capture the device endianness when it gets
> >>> reset.
> >>>
> >>> We migrate this property in a subsection, after the device descriptor. This
> >>> means the load code must not rely on it until it is restored. As a consequence,
> >>> the vring sanity checks had to be moved after the call to vmstate_load_state().
> >>> We enforce paranoia by poisoning the property at the begining of virtio_load().
> >>>
> >>> Signed-off-by: Greg Kurz <gkurz@linux.vnet.ibm.com>
> >>> ---
> >>>
> >>>    Changes since last version (virtio migration RFC):
> >>>    - endianness cached at device reset time
> >>>    - reworked migration support
> >>>
> >>>    hw/virtio/virtio-pci.c     |    8 ++--
> >>>    hw/virtio/virtio.c         |  100 +++++++++++++++++++++++++++++++++++++++-----
> >>>    include/hw/virtio/virtio.h |   12 ++++-
> >>>    3 files changed, 102 insertions(+), 18 deletions(-)
> >>>
> >>> diff --git a/hw/virtio/virtio-pci.c b/hw/virtio/virtio-pci.c
> >>> index 390c8d2..2ffceb8 100644
> >>> --- a/hw/virtio/virtio-pci.c
> >>> +++ b/hw/virtio/virtio-pci.c
> >>> @@ -406,13 +406,13 @@ static uint64_t virtio_pci_config_read(void *opaque, hwaddr addr,
> >>>            break;
> >>>        case 2:
> >>>            val = virtio_config_readw(vdev, addr);
> >>> -        if (virtio_is_big_endian()) {
> >>> +        if (virtio_is_big_endian(vdev)) {
> >>>                val = bswap16(val);
> >>>            }
> >>>            break;
> >>>        case 4:
> >>>            val = virtio_config_readl(vdev, addr);
> >>> -        if (virtio_is_big_endian()) {
> >>> +        if (virtio_is_big_endian(vdev)) {
> >>>                val = bswap32(val);
> >>>            }
> >>>            break;
> >>> @@ -440,13 +440,13 @@ static void virtio_pci_config_write(void *opaque, hwaddr addr,
> >>>            virtio_config_writeb(vdev, addr, val);
> >>>            break;
> >>>        case 2:
> >>> -        if (virtio_is_big_endian()) {
> >>> +        if (virtio_is_big_endian(vdev)) {
> >>>                val = bswap16(val);
> >>>            }
> >>>            virtio_config_writew(vdev, addr, val);
> >>>            break;
> >>>        case 4:
> >>> -        if (virtio_is_big_endian()) {
> >>> +        if (virtio_is_big_endian(vdev)) {
> >>>                val = bswap32(val);
> >>>            }
> >>>            virtio_config_writel(vdev, addr, val);
> >>> diff --git a/hw/virtio/virtio.c b/hw/virtio/virtio.c
> >>> index 16b73d9..6235df8 100644
> >>> --- a/hw/virtio/virtio.c
> >>> +++ b/hw/virtio/virtio.c
> >>> @@ -545,6 +545,24 @@ void virtio_set_status(VirtIODevice *vdev, uint8_t val)
> >>>        vdev->status = val;
> >>>    }
> >>>    
> >>> +static void virtio_set_endian_target_default(VirtIODevice *vdev)
> >>> +{
> >>> +#ifdef TARGET_WORDS_BIGENDIAN
> >>> +    vdev->device_endian = VIRTIO_DEVICE_ENDIAN_BIG;
> >>> +#else
> >>> +    vdev->device_endian = VIRTIO_DEVICE_ENDIAN_LITTLE;
> >>> +#endif
> >>> +}
> >>> +
> >>> +static void virtio_set_endian_cpu(VirtIODevice *vdev, CPUState *cpu)
> >>> +{
> >>> +    if (cpu_virtio_is_big_endian(cpu)) {
> >>> +        vdev->device_endian = VIRTIO_DEVICE_ENDIAN_BIG;
> >>> +    } else {
> >>> +        vdev->device_endian = VIRTIO_DEVICE_ENDIAN_LITTLE;
> >>> +    }
> >>> +}
> >>> +
> >>>    void virtio_reset(void *opaque)
> >>>    {
> >>>        VirtIODevice *vdev = opaque;
> >>> @@ -552,6 +570,13 @@ void virtio_reset(void *opaque)
> >>>        int i;
> >>>    
> >>>        virtio_set_status(vdev, 0);
> >>> +    if (current_cpu) {
> >>> +        /* Guest initiated reset */
> >>> +        virtio_set_endian_cpu(vdev, current_cpu);
> >>> +    } else {
> >>> +        /* System reset */
> >>> +        virtio_set_endian_target_default(vdev);
> >>> +    }
> >>>    
> >>>        if (k->reset) {
> >>>            k->reset(vdev);
> >>> @@ -840,6 +865,28 @@ void virtio_notify_config(VirtIODevice *vdev)
> >>>        virtio_notify_vector(vdev, vdev->config_vector);
> >>>    }
> >>>    
> >>> +static bool virtio_device_endian_needed(void *opaque)
> >>> +{
> >>> +    VirtIODevice *vdev = opaque;
> >>> +
> >>> +    assert(vdev->device_endian != VIRTIO_DEVICE_ENDIAN_UNKNOWN);
> >>> +#ifdef TARGET_WORDS_BIGENDIAN
> >>> +    return vdev->device_endian == VIRTIO_DEVICE_ENDIAN_LITTLE;
> >>> +#else
> >>> +    return vdev->device_endian == VIRTIO_DEVICE_ENDIAN_BIG;
> >>> +#endif
> >> if (target_words_bigendian()) {
> >>       return virtio_is_big_endian();
> >> } else {
> >>       return !virtio_is_big_endian();
> >> }
> >>
> >> Then we have one less dependency on TARGET_WORDS_BIGENDIAN which means a
> >> step towards compiling virtio once ;).
> >>
> >>
> >> Alex
> >>
> > Heh ! It used to be target_words_bigendian() in the first place and I turned
> > it into TARGET_WORDS_BIGENDIAN to avoid "hey virtio isn't soon to be common
> > why don't you sort this out at compile time?" remarks. :)
> >
> > Since we are definitely not on a fastpath here, I'll gladly fix this.
> 
> Yeah, just combine it with virtio_set_endian_target_default.
> 
> static enum foo virtio_default_endian(vdev)
> {
>      if (target_words_bigendian()) {
>          return VIRTIO_DEVICE_ENDIAN_BIG;
>      ....
> }
> 
> Instead of calling virtio_set_endian_target_default, you do
> 
>      vdev->device_endian = virtio_default_endian(vdev);
> 
> and
> 
> static bool virtio_biendian_section_needed(vdev)
> {
>      assert(unknown);
>      return vdev->device_endian != virtio_default_endian(vdev);
> }
> 
> 
> Alex
> 

It sure looks better. Thanks !

-- 
Gregory Kurz                                     kurzgreg@fr.ibm.com
                                                 gkurz@linux.vnet.ibm.com
Software Engineer @ IBM/Meiosys                  http://www.ibm.com
Tel +33 (0)562 165 496

"Anarchy is about taking complete responsibility for yourself."
        Alan Moore.