[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
Re: [Qemu-devel] [PATCH 1/7] virtio: allow byte swapping for vring and c
From: |
Anthony Liguori |
Subject: |
Re: [Qemu-devel] [PATCH 1/7] virtio: allow byte swapping for vring and config access |
Date: |
Thu, 08 Aug 2013 10:40:28 -0500 |
User-agent: |
Notmuch/0.15.2+202~g0c4b8aa (http://notmuchmail.org) Emacs/23.3.1 (x86_64-pc-linux-gnu) |
Andreas Färber <address@hidden> writes:
> Am 08.08.2013 15:31, schrieb Anthony Liguori:
>> Rusty Russell <address@hidden> writes:
>>
>>> Virtio is currently defined to work as "guest endian", but this is a
>>> problem if the guest can change endian. As most targets can't change
>>> endian, we make it a per-target option to avoid pessimising.
>>>
>>> This is based on a simpler patch by Anthony Liguouri, which only handled
>>> the vring accesses. We also need some drivers to access these helpers,
>>> eg. for data which contains headers.
>>>
>>> Signed-off-by: Rusty Russell <address@hidden>
>>> ---
>>> hw/virtio/virtio.c | 46 +++++++++----
>>> include/hw/virtio/virtio-access.h | 138
>>> ++++++++++++++++++++++++++++++++++++++
>>> 2 files changed, 170 insertions(+), 14 deletions(-)
>>> create mode 100644 include/hw/virtio/virtio-access.h
>>>
>>> diff --git a/hw/virtio/virtio.c b/hw/virtio/virtio.c
>>> index 8176c14..2887f17 100644
>>> --- a/hw/virtio/virtio.c
>>> +++ b/hw/virtio/virtio.c
>>> @@ -18,6 +18,7 @@
>>> #include "hw/virtio/virtio.h"
>>> #include "qemu/atomic.h"
>>> #include "hw/virtio/virtio-bus.h"
>>> +#include "hw/virtio/virtio-access.h"
>>>
>>> /* The alignment to use between consumer and producer parts of vring.
>>> * x86 pagesize again. */
>>> @@ -84,6 +85,20 @@ struct VirtQueue
>>> EventNotifier host_notifier;
>>> };
>>>
>>> +#ifdef TARGET_VIRTIO_SWAPENDIAN
>>> +bool virtio_byteswap;
>>> +
>>> +/* Ask target code if we should swap endian for all vring and config
>>> access. */
>>> +static void mark_endian(void)
>>> +{
>>> + virtio_byteswap = virtio_swap_endian();
>>> +}
>>> +#else
>>> +static void mark_endian(void)
>>> +{
>>> +}
>>> +#endif
>>> +
>>
>> It would be very good to avoid a target specific define here. We would
>> like to move to only building a single copy of the virtio code.
>
> +1
>
>> We have a mechanism to do weak functions via stubs/. I think it would
>> be better to do cpu_get_byteswap() as a stub function and then overload
>> it in the ppc64 code.
>
> If this as your name indicates is a per-CPU function then it should go
> into CPUClass. Interesting question is, what is virtio supposed to do if
> we have two ppc CPUs, one is Big Endian, the other is Little Endian.
PPC64 is big endian. AFAIK, there is no such thing as a little endian
PPC64 processor.
This is just a processor mode where loads/stores are byte lane swapped.
Hence the name 'cpu_get_byteswap'. It's just asking whether the
load/stores are being swapped or not.
At least for PPC64, it's not possible to enable/disable byte lane
swapping for individual CPUs. It's done through a system-wide hcall.
FWIW, I think most bi-endian architectures are this way too so I think
this is equally applicable to ARM. Peter, is that right?
Regards,
Anthony Liguori
> We'd need to check current_cpu then, which for Xen is always NULL.
>
> Andreas
>
> --
> SUSE LINUX Products GmbH, Maxfeldstr. 5, 90409 Nürnberg, Germany
> GF: Jeff Hawn, Jennifer Guild, Felix Imendörffer; HRB 16746 AG Nürnberg
- [Qemu-devel] [PATCH 7/7] hw/char/virtio-serial-bus: use virtio wrappers to access headers., (continued)
- [Qemu-devel] [PATCH 7/7] hw/char/virtio-serial-bus: use virtio wrappers to access headers., Rusty Russell, 2013/08/08
- [Qemu-devel] [PATCH 2/7] target-ppc: ppc64 targets can be either endian., Rusty Russell, 2013/08/08
- [Qemu-devel] [PATCH 4/7] hw/net/virtio-balloon: use virtio wrappers to access page frame numbers., Rusty Russell, 2013/08/08
- [Qemu-devel] [PATCH 6/7] hw/scsi/virtio-scsi: use virtio wrappers to access headers., Rusty Russell, 2013/08/08
- [Qemu-devel] [PATCH 1/7] virtio: allow byte swapping for vring and config access, Rusty Russell, 2013/08/08
- Re: [Qemu-devel] [PATCH 1/7] virtio: allow byte swapping for vring and config access, Anthony Liguori, 2013/08/08
- Re: [Qemu-devel] [PATCH 1/7] virtio: allow byte swapping for vring and config access, Andreas Färber, 2013/08/08
- Re: [Qemu-devel] [PATCH 1/7] virtio: allow byte swapping for vring and config access,
Anthony Liguori <=
- Re: [Qemu-devel] [PATCH 1/7] virtio: allow byte swapping for vring and config access, Daniel P. Berrange, 2013/08/08
- Re: [Qemu-devel] [PATCH 1/7] virtio: allow byte swapping for vring and config access, Anthony Liguori, 2013/08/08
- Re: [Qemu-devel] [PATCH 1/7] virtio: allow byte swapping for vring and config access, Peter Maydell, 2013/08/08
- Re: [Qemu-devel] [PATCH 1/7] virtio: allow byte swapping for vring and config access, Anthony Liguori, 2013/08/08
- Re: [Qemu-devel] [PATCH 1/7] virtio: allow byte swapping for vring and config access, Peter Maydell, 2013/08/08
- Re: [Qemu-devel] [PATCH 1/7] virtio: allow byte swapping for vring and config access, Rusty Russell, 2013/08/08
- Re: [Qemu-devel] [PATCH 1/7] virtio: allow byte swapping for vring and config access, Anton Blanchard, 2013/08/09
- Re: [Qemu-devel] [PATCH 1/7] virtio: allow byte swapping for vring and config access, Peter Maydell, 2013/08/09
- Re: [Qemu-devel] [PATCH 1/7] virtio: allow byte swapping for vring and config access, Anthony Liguori, 2013/08/09
- Re: [Qemu-devel] [PATCH 1/7] virtio: allow byte swapping for vring and config access, Peter Maydell, 2013/08/08