[PULL] virtio/vhost: cross endian support
The following changes since commit 8a7b19d8b542b87bccc3eaaf81dcc90a5ca48aea: include/uapi/linux/virtio_balloon.h: include linux/virtio_types.h (2015-06-01 15:46:54 +0200) are available in the git repository at: git://git.kernel.org/pub/scm/linux/kernel/git/mst/vhost.git tags/for_linus for you to fetch changes up to 59a5b0f7bf74f88da6670bcbf924d8cc1e75b1ee: virtio-pci: alloc only resources actually used. (2015-06-24 08:15:09 +0200) virtio/vhost: cross endian support I have just queued some more bugfix patches today but none fix regressions and none are related to these ones, so it looks like a good time for a merge for -rc1. Signed-off-by: Michael S. Tsirkin Gerd Hoffmann (1): virtio-pci: alloc only resources actually used. Greg Kurz (8): virtio: introduce virtio_is_little_endian() helper tun: add tun_is_little_endian() helper macvtap: introduce macvtap_is_little_endian() helper vringh: introduce vringh_is_little_endian() helper vhost: introduce vhost_is_little_endian() helper virtio: add explicit big-endian support to memory accessors vhost: cross-endian support for legacy devices macvtap/tun: cross-endian support for little-endian hosts drivers/vhost/vhost.h | 25 --- drivers/virtio/virtio_pci_common.h | 2 + include/linux/virtio_byteorder.h | 24 ++- include/linux/virtio_config.h | 18 +--- include/linux/vringh.h | 18 +--- include/uapi/linux/if_tun.h| 6 +++ include/uapi/linux/vhost.h | 14 +++ drivers/net/macvtap.c | 65 - drivers/net/tun.c | 67 +- drivers/vhost/vhost.c | 85 +- drivers/virtio/virtio_pci_common.c | 7 drivers/virtio/virtio_pci_legacy.c | 13 +- drivers/virtio/virtio_pci_modern.c | 24 --- drivers/net/Kconfig| 14 +++ drivers/vhost/Kconfig | 15 +++ 15 files changed, 350 insertions(+), 47 deletions(-) ___ Virtualization mailing list Virtualization@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/virtualization
Re: [PULL] virtio/vhost: cross endian support
On Wed, Jul 1, 2015 at 2:31 AM, Michael S. Tsirkin wrote: > virtio/vhost: cross endian support Ugh. Does this really have to be dynamic? Can't virtio do the sane thing, and just use a _fixed_ endianness? Doing a unconditional byte swap is faster and simpler than the crazy conditionals. That's true regardless of endianness, but gets to be even more so if the fixed endianness is little-endian, since BE is not-so-slowly fading from the world. Linus ___ Virtualization mailing list Virtualization@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/virtualization
Re: [PULL] virtio/vhost: cross endian support
On Wed, Jul 1, 2015 at 12:02 PM, Linus Torvalds wrote: > > Doing a unconditional byte swap is faster and simpler than the crazy > conditionals. Unconditional endianness not only makes for simpler and faster code, it also ends up being easier to debug and add things like type annotations for sparse. Linus ___ Virtualization mailing list Virtualization@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/virtualization
Re: [PULL] virtio/vhost: cross endian support
On Wed, Jul 01, 2015 at 12:02:50PM -0700, Linus Torvalds wrote: > On Wed, Jul 1, 2015 at 2:31 AM, Michael S. Tsirkin wrote: > > virtio/vhost: cross endian support > > Ugh. Does this really have to be dynamic? > > Can't virtio do the sane thing, and just use a _fixed_ endianness? > > Doing a unconditional byte swap is faster and simpler than the crazy > conditionals. That's true regardless of endianness, but gets to be > even more so if the fixed endianness is little-endian, since BE is > not-so-slowly fading from the world. > >Linus Yea, well - support for legacy BE guests on the new LE hosts is exactly the motivation for this. I dislike it too, but there are two redeeming properties that made me merge this: 1. It's a trivial amount of code: since we wrap host/guest accesses anyway, almost all of it is well hidden from drivers. 2. Sane platforms would never set flags like VHOST_CROSS_ENDIAN_LEGACY - and when it's clear, there's zero overhead (as some point it was tested by compiling with and without the patches, got the same stripped binary). Maybe we could create a Kconfig symbol to enforce point (2): prevent people from enabling it e.g. on x86. I will look into this - but it can be done by a patch on top, so I think this can be merged as is. Or do you know of someone using kernel with all config options enabled undiscriminately? Thanks, -- MST ___ Virtualization mailing list Virtualization@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/virtualization
Re: [PULL] virtio/vhost: cross endian support
On Wed, Jul 01, 2015 at 12:03:59PM -0700, Linus Torvalds wrote: > On Wed, Jul 1, 2015 at 12:02 PM, Linus Torvalds > wrote: > > > > Doing a unconditional byte swap is faster and simpler than the crazy > > conditionals. > > Unconditional endianness not only makes for simpler and faster code, > it also ends up being easier to debug and add things like type > annotations for sparse. > > Linus At least this last one is well covered by these patches: this uses separate sparse types so all accesses are statically verified by sparse to use the correct accessor. -- MST ___ Virtualization mailing list Virtualization@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/virtualization
Re: [PULL] virtio/vhost: cross endian support
On Thu, 2 Jul 2015 08:01:28 +0200 "Michael S. Tsirkin" wrote: > On Wed, Jul 01, 2015 at 12:02:50PM -0700, Linus Torvalds wrote: > > On Wed, Jul 1, 2015 at 2:31 AM, Michael S. Tsirkin wrote: > > > virtio/vhost: cross endian support > > > > Ugh. Does this really have to be dynamic? > > > > Can't virtio do the sane thing, and just use a _fixed_ endianness? > > > > Doing a unconditional byte swap is faster and simpler than the crazy > > conditionals. That's true regardless of endianness, but gets to be > > even more so if the fixed endianness is little-endian, since BE is > > not-so-slowly fading from the world. > > > >Linus > > Yea, well - support for legacy BE guests on the new LE hosts is > exactly the motivation for this. > > I dislike it too, but there are two redeeming properties that > made me merge this: > > 1. It's a trivial amount of code: since we wrap host/guest accesses > anyway, almost all of it is well hidden from drivers. > > 2. Sane platforms would never set flags like VHOST_CROSS_ENDIAN_LEGACY - > and when it's clear, there's zero overhead (as some point it was > tested by compiling with and without the patches, got the same > stripped binary). > > Maybe we could create a Kconfig symbol to enforce point (2): prevent > people from enabling it e.g. on x86. I will look into this - but it can > be done by a patch on top, so I think this can be merged as is. > This cross-endian *oddity* is targeting PowerPC book3s_64 processors... I am not aware of any other users. Maybe create a symbol that would be only selected by PPC_BOOK3S_64 ? > Or do you know of someone using kernel with all config options enabled > undiscriminately? > > Thanks, > ___ Virtualization mailing list Virtualization@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/virtualization
Re: [PULL] virtio/vhost: cross endian support
On Thu, Jul 02, 2015 at 11:12:56AM +0200, Greg Kurz wrote: > On Thu, 2 Jul 2015 08:01:28 +0200 > "Michael S. Tsirkin" wrote: > > > On Wed, Jul 01, 2015 at 12:02:50PM -0700, Linus Torvalds wrote: > > > On Wed, Jul 1, 2015 at 2:31 AM, Michael S. Tsirkin > > > wrote: > > > > virtio/vhost: cross endian support > > > > > > Ugh. Does this really have to be dynamic? > > > > > > Can't virtio do the sane thing, and just use a _fixed_ endianness? > > > > > > Doing a unconditional byte swap is faster and simpler than the crazy > > > conditionals. That's true regardless of endianness, but gets to be > > > even more so if the fixed endianness is little-endian, since BE is > > > not-so-slowly fading from the world. > > > > > >Linus > > > > Yea, well - support for legacy BE guests on the new LE hosts is > > exactly the motivation for this. > > > > I dislike it too, but there are two redeeming properties that > > made me merge this: > > > > 1. It's a trivial amount of code: since we wrap host/guest accesses > > anyway, almost all of it is well hidden from drivers. > > > > 2. Sane platforms would never set flags like VHOST_CROSS_ENDIAN_LEGACY - > > and when it's clear, there's zero overhead (as some point it was > > tested by compiling with and without the patches, got the same > > stripped binary). > > > > Maybe we could create a Kconfig symbol to enforce point (2): prevent > > people from enabling it e.g. on x86. I will look into this - but it can > > be done by a patch on top, so I think this can be merged as is. > > > > This cross-endian *oddity* is targeting PowerPC book3s_64 processors... I > am not aware of any other users. Maybe create a symbol that would > be only selected by PPC_BOOK3S_64 ? I think some ARM systems are trying to support cross-endian configurations as well. Besides that, yes, this is more or less what I had in mind. > > > Or do you know of someone using kernel with all config options enabled > > undiscriminately? > > > > Thanks, > > ___ Virtualization mailing list Virtualization@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/virtualization
Re: [PULL] virtio/vhost: cross endian support
On Thu, Jul 02, 2015 at 08:01:28AM +0200, Michael S. Tsirkin wrote: > On Wed, Jul 01, 2015 at 12:02:50PM -0700, Linus Torvalds wrote: > > On Wed, Jul 1, 2015 at 2:31 AM, Michael S. Tsirkin wrote: > > > virtio/vhost: cross endian support > > > > Ugh. Does this really have to be dynamic? > > > > Can't virtio do the sane thing, and just use a _fixed_ endianness? > > > > Doing a unconditional byte swap is faster and simpler than the crazy > > conditionals. That's true regardless of endianness, but gets to be > > even more so if the fixed endianness is little-endian, since BE is > > not-so-slowly fading from the world. > > > >Linus > > Yea, well - support for legacy BE guests on the new LE hosts is > exactly the motivation for this. > > I dislike it too, but there are two redeeming properties that > made me merge this: > > 1. It's a trivial amount of code: since we wrap host/guest accesses > anyway, almost all of it is well hidden from drivers. > > 2. Sane platforms would never set flags like VHOST_CROSS_ENDIAN_LEGACY - > and when it's clear, there's zero overhead (as some point it was > tested by compiling with and without the patches, got the same > stripped binary). > > Maybe we could create a Kconfig symbol to enforce point (2): prevent > people from enabling it e.g. on x86. I will look into this - but it can > be done by a patch on top, so I think this can be merged as is. Linus, could you please clarify whether making the feature depend on the cross-endian guest support would address your comment, and whether you think this can be merged as is, and the dependency added after -rc1? > Or do you know of someone using kernel with all config options enabled > undiscriminately? > > Thanks, > > -- > MST ___ Virtualization mailing list Virtualization@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/virtualization
Re: [PULL] virtio/vhost: cross endian support
On Fri, Jul 3, 2015 at 12:59 AM, Michael S. Tsirkin wrote: > > Linus, could you please clarify whether making the > feature depend on the cross-endian guest support > would address your comment, and whether you think > this can be merged as is, and the dependency added > after -rc1? I'll take it. I still think dynamic byte order is a fundamental (and much too common) mistake, but whatever. Linus ___ Virtualization mailing list Virtualization@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/virtualization
Re: [PULL] virtio/vhost: cross endian support
On Thu, 2 Jul 2015 11:32:52 +0200 "Michael S. Tsirkin" wrote: > On Thu, Jul 02, 2015 at 11:12:56AM +0200, Greg Kurz wrote: > > On Thu, 2 Jul 2015 08:01:28 +0200 > > "Michael S. Tsirkin" wrote: ... > > > Yea, well - support for legacy BE guests on the new LE hosts is > > > exactly the motivation for this. > > > > > > I dislike it too, but there are two redeeming properties that > > > made me merge this: > > > > > > 1. It's a trivial amount of code: since we wrap host/guest accesses > > > anyway, almost all of it is well hidden from drivers. > > > > > > 2. Sane platforms would never set flags like VHOST_CROSS_ENDIAN_LEGACY - > > > and when it's clear, there's zero overhead (as some point it was > > > tested by compiling with and without the patches, got the same > > > stripped binary). > > > > > > Maybe we could create a Kconfig symbol to enforce point (2): prevent > > > people from enabling it e.g. on x86. I will look into this - but it can > > > be done by a patch on top, so I think this can be merged as is. > > > > > > > This cross-endian *oddity* is targeting PowerPC book3s_64 processors... I > > am not aware of any other users. Maybe create a symbol that would > > be only selected by PPC_BOOK3S_64 ? > > I think some ARM systems are trying to support cross-endian > configurations as well. > > Besides that, yes, this is more or less what I had in mind. Would something simple like this already do the job: diff --git a/drivers/vhost/Kconfig b/drivers/vhost/Kconfig --- a/drivers/vhost/Kconfig +++ b/drivers/vhost/Kconfig @@ -35,6 +35,7 @@ config VHOST config VHOST_CROSS_ENDIAN_LEGACY bool "Cross-endian support for vhost" + depends on KVM_BOOK3S_64 || KVM_ARM_HOST default n ---help--- This option allows vhost to support guests with a different byte ? If that looks acceptable, I can submit a proper patch if you like. Thomas ___ Virtualization mailing list Virtualization@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/virtualization
Re: [PULL] virtio/vhost: cross endian support
On Tue, Jul 07, 2015 at 06:36:53PM +0200, Thomas Huth wrote: > On Thu, 2 Jul 2015 11:32:52 +0200 > "Michael S. Tsirkin" wrote: > > > On Thu, Jul 02, 2015 at 11:12:56AM +0200, Greg Kurz wrote: > > > On Thu, 2 Jul 2015 08:01:28 +0200 > > > "Michael S. Tsirkin" wrote: > ... > > > > Yea, well - support for legacy BE guests on the new LE hosts is > > > > exactly the motivation for this. > > > > > > > > I dislike it too, but there are two redeeming properties that > > > > made me merge this: > > > > > > > > 1. It's a trivial amount of code: since we wrap host/guest accesses > > > > anyway, almost all of it is well hidden from drivers. > > > > > > > > 2. Sane platforms would never set flags like VHOST_CROSS_ENDIAN_LEGACY > > > > - > > > > and when it's clear, there's zero overhead (as some point it was > > > > tested by compiling with and without the patches, got the same > > > > stripped binary). > > > > > > > > Maybe we could create a Kconfig symbol to enforce point (2): prevent > > > > people from enabling it e.g. on x86. I will look into this - but it can > > > > be done by a patch on top, so I think this can be merged as is. > > > > > > > > > > This cross-endian *oddity* is targeting PowerPC book3s_64 processors... I > > > am not aware of any other users. Maybe create a symbol that would > > > be only selected by PPC_BOOK3S_64 ? > > > > I think some ARM systems are trying to support cross-endian > > configurations as well. > > > > Besides that, yes, this is more or less what I had in mind. > > Would something simple like this already do the job: > > diff --git a/drivers/vhost/Kconfig b/drivers/vhost/Kconfig > --- a/drivers/vhost/Kconfig > +++ b/drivers/vhost/Kconfig > @@ -35,6 +35,7 @@ config VHOST > > config VHOST_CROSS_ENDIAN_LEGACY > bool "Cross-endian support for vhost" > + depends on KVM_BOOK3S_64 || KVM_ARM_HOST > default n > ---help--- > This option allows vhost to support guests with a different byte > > ? Do all ARM hosts support this dynamic endian-ness? > If that looks acceptable, I can submit a proper patch if you like. > > Thomas I think I prefer some kind of symbol defined by these arches, so I don't get to maintain an arch list in vhost. -- MST ___ Virtualization mailing list Virtualization@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/virtualization
