Michael S. Tsirkin
2015-Jun-24 14:17 UTC
[PATCH RFC] vhost: add ioctl to query nregions upper limit
On Wed, Jun 24, 2015 at 04:07:27PM +0200, Igor Mammedov wrote:> On Wed, 24 Jun 2015 15:49:27 +0200 > "Michael S. Tsirkin" <mst at redhat.com> wrote: > > > Userspace currently simply tries to give vhost as many regions > > as it happens to have, but you only have the mem table > > when you have initialized a large part of VM, so graceful > > failure is very hard to support. > > > > The result is that userspace tends to fail catastrophically. > > > > Instead, add a new ioctl so userspace can find out how much kernel > > supports, up front. This returns a positive value that we commit to. > > > > Also, document our contract with legacy userspace: when running on an > > old kernel, you get -1 and you can assume at least 64 slots. Since 0 > > value's left unused, let's make that mean that the current userspace > > behaviour (trial and error) is required, just in case we want it back. > > > > Signed-off-by: Michael S. Tsirkin <mst at redhat.com> > > Cc: Igor Mammedov <imammedo at redhat.com> > > Cc: Paolo Bonzini <pbonzini at redhat.com> > > --- > > include/uapi/linux/vhost.h | 17 ++++++++++++++++- > > drivers/vhost/vhost.c | 5 +++++ > > 2 files changed, 21 insertions(+), 1 deletion(-) > > > > diff --git a/include/uapi/linux/vhost.h b/include/uapi/linux/vhost.h > > index ab373191..f71fa6d 100644 > > --- a/include/uapi/linux/vhost.h > > +++ b/include/uapi/linux/vhost.h > > @@ -80,7 +80,7 @@ struct vhost_memory { > > * Allows subsequent call to VHOST_OWNER_SET to succeed. */ > > #define VHOST_RESET_OWNER _IO(VHOST_VIRTIO, 0x02) > > > > -/* Set up/modify memory layout */ > > +/* Set up/modify memory layout: see also VHOST_GET_MEM_MAX_NREGIONS below. */ > > #define VHOST_SET_MEM_TABLE _IOW(VHOST_VIRTIO, 0x03, struct vhost_memory) > > > > /* Write logging setup. */ > > @@ -127,6 +127,21 @@ struct vhost_memory { > > /* Set eventfd to signal an error */ > > #define VHOST_SET_VRING_ERR _IOW(VHOST_VIRTIO, 0x22, struct vhost_vring_file) > > > > +/* Query upper limit on nregions in VHOST_SET_MEM_TABLE arguments. > > + * Returns: > > + * 0 < value <= MAX_INT - gives the upper limit, higher values will fail > > + * 0 - there's no static limit: try and see if it works > > + * -1 - on failure > > + */ > > +#define VHOST_GET_MEM_MAX_NREGIONS _IO(VHOST_VIRTIO, 0x23) > > + > > +/* Returned by VHOST_GET_MEM_MAX_NREGIONS to mean there's no static limit: > > + * try and it'll work if you are lucky. */ > > +#define VHOST_MEM_MAX_NREGIONS_NONE 0 > is it needed? we always have a limit, > or don't have IOCTL => -1 => old try and see way > > > +/* We support at least as many nregions in VHOST_SET_MEM_TABLE: > > + * for use on legacy kernels without VHOST_GET_MEM_MAX_NREGIONS support. */ > > +#define VHOST_MEM_MAX_NREGIONS_DEFAULT 64 > ^^^ not used below, > if it's for legacy then perhaps s/DEFAULT/LEGACY/The assumption was that userspace detecting old kernels will just use 64, this means we do want a flag to get the old way. OTOH if you won't think it's useful, let me know.> > + > > /* VHOST_NET specific defines */ > > > > /* Attach virtio net ring to a raw socket, or tap device. > > diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c > > index 9e8e004..3b68f9d 100644 > > --- a/drivers/vhost/vhost.c > > +++ b/drivers/vhost/vhost.c > > @@ -917,6 +917,11 @@ long vhost_dev_ioctl(struct vhost_dev *d, unsigned int ioctl, void __user *argp) > > long r; > > int i, fd; > > > > + if (ioctl == VHOST_GET_MEM_MAX_NREGIONS) { > > + r = VHOST_MEMORY_MAX_NREGIONS; > > + goto done; > > + } > > + > > /* If you are not the owner, you can become one */ > > if (ioctl == VHOST_SET_OWNER) { > > r = vhost_dev_set_owner(d);
Igor Mammedov
2015-Jun-24 14:52 UTC
[PATCH RFC] vhost: add ioctl to query nregions upper limit
On Wed, 24 Jun 2015 16:17:46 +0200 "Michael S. Tsirkin" <mst at redhat.com> wrote:> On Wed, Jun 24, 2015 at 04:07:27PM +0200, Igor Mammedov wrote: > > On Wed, 24 Jun 2015 15:49:27 +0200 > > "Michael S. Tsirkin" <mst at redhat.com> wrote: > > > > > Userspace currently simply tries to give vhost as many regions > > > as it happens to have, but you only have the mem table > > > when you have initialized a large part of VM, so graceful > > > failure is very hard to support. > > > > > > The result is that userspace tends to fail catastrophically. > > > > > > Instead, add a new ioctl so userspace can find out how much kernel > > > supports, up front. This returns a positive value that we commit to. > > > > > > Also, document our contract with legacy userspace: when running on an > > > old kernel, you get -1 and you can assume at least 64 slots. Since 0 > > > value's left unused, let's make that mean that the current userspace > > > behaviour (trial and error) is required, just in case we want it back. > > > > > > Signed-off-by: Michael S. Tsirkin <mst at redhat.com> > > > Cc: Igor Mammedov <imammedo at redhat.com> > > > Cc: Paolo Bonzini <pbonzini at redhat.com> > > > --- > > > include/uapi/linux/vhost.h | 17 ++++++++++++++++- > > > drivers/vhost/vhost.c | 5 +++++ > > > 2 files changed, 21 insertions(+), 1 deletion(-) > > > > > > diff --git a/include/uapi/linux/vhost.h b/include/uapi/linux/vhost.h > > > index ab373191..f71fa6d 100644 > > > --- a/include/uapi/linux/vhost.h > > > +++ b/include/uapi/linux/vhost.h > > > @@ -80,7 +80,7 @@ struct vhost_memory { > > > * Allows subsequent call to VHOST_OWNER_SET to succeed. */ > > > #define VHOST_RESET_OWNER _IO(VHOST_VIRTIO, 0x02) > > > > > > -/* Set up/modify memory layout */ > > > +/* Set up/modify memory layout: see also VHOST_GET_MEM_MAX_NREGIONS below. */ > > > #define VHOST_SET_MEM_TABLE _IOW(VHOST_VIRTIO, 0x03, struct vhost_memory) > > > > > > /* Write logging setup. */ > > > @@ -127,6 +127,21 @@ struct vhost_memory { > > > /* Set eventfd to signal an error */ > > > #define VHOST_SET_VRING_ERR _IOW(VHOST_VIRTIO, 0x22, struct vhost_vring_file) > > > > > > +/* Query upper limit on nregions in VHOST_SET_MEM_TABLE arguments. > > > + * Returns: > > > + * 0 < value <= MAX_INT - gives the upper limit, higher values will fail > > > + * 0 - there's no static limit: try and see if it works > > > + * -1 - on failure > > > + */ > > > +#define VHOST_GET_MEM_MAX_NREGIONS _IO(VHOST_VIRTIO, 0x23) > > > + > > > +/* Returned by VHOST_GET_MEM_MAX_NREGIONS to mean there's no static limit: > > > + * try and it'll work if you are lucky. */ > > > +#define VHOST_MEM_MAX_NREGIONS_NONE 0 > > is it needed? we always have a limit, > > or don't have IOCTL => -1 => old try and see way > > > > > +/* We support at least as many nregions in VHOST_SET_MEM_TABLE: > > > + * for use on legacy kernels without VHOST_GET_MEM_MAX_NREGIONS support. */ > > > +#define VHOST_MEM_MAX_NREGIONS_DEFAULT 64 > > ^^^ not used below, > > if it's for legacy then perhaps s/DEFAULT/LEGACY/ > > The assumption was that userspace detecting old kernels will just use 64, > this means we do want a flag to get the old way. > > OTOH if you won't think it's useful, let me know.this header will be synced into QEMU's tree so that we could use this define there, isn't it? IMHO then _LEGACY is more exact description of macro. As for 0 return value, -1 is just fine for detecting old kernels (i.e. try and see if it works), so 0 looks unnecessary but it doesn't in any way hurt either. For me limit or -1 is enough to try fix userspace.> > > > + > > > /* VHOST_NET specific defines */ > > > > > > /* Attach virtio net ring to a raw socket, or tap device. > > > diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c > > > index 9e8e004..3b68f9d 100644 > > > --- a/drivers/vhost/vhost.c > > > +++ b/drivers/vhost/vhost.c > > > @@ -917,6 +917,11 @@ long vhost_dev_ioctl(struct vhost_dev *d, unsigned int ioctl, void __user *argp) > > > long r; > > > int i, fd; > > > > > > + if (ioctl == VHOST_GET_MEM_MAX_NREGIONS) { > > > + r = VHOST_MEMORY_MAX_NREGIONS; > > > + goto done; > > > + } > > > + > > > /* If you are not the owner, you can become one */ > > > if (ioctl == VHOST_SET_OWNER) { > > > r = vhost_dev_set_owner(d); > -- > To unsubscribe from this list: send the line "unsubscribe kvm" in > the body of a message to majordomo at vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html
Michael S. Tsirkin
2015-Jun-24 15:08 UTC
[PATCH RFC] vhost: add ioctl to query nregions upper limit
On Wed, Jun 24, 2015 at 04:52:29PM +0200, Igor Mammedov wrote:> On Wed, 24 Jun 2015 16:17:46 +0200 > "Michael S. Tsirkin" <mst at redhat.com> wrote: > > > On Wed, Jun 24, 2015 at 04:07:27PM +0200, Igor Mammedov wrote: > > > On Wed, 24 Jun 2015 15:49:27 +0200 > > > "Michael S. Tsirkin" <mst at redhat.com> wrote: > > > > > > > Userspace currently simply tries to give vhost as many regions > > > > as it happens to have, but you only have the mem table > > > > when you have initialized a large part of VM, so graceful > > > > failure is very hard to support. > > > > > > > > The result is that userspace tends to fail catastrophically. > > > > > > > > Instead, add a new ioctl so userspace can find out how much kernel > > > > supports, up front. This returns a positive value that we commit to. > > > > > > > > Also, document our contract with legacy userspace: when running on an > > > > old kernel, you get -1 and you can assume at least 64 slots. Since 0 > > > > value's left unused, let's make that mean that the current userspace > > > > behaviour (trial and error) is required, just in case we want it back. > > > > > > > > Signed-off-by: Michael S. Tsirkin <mst at redhat.com> > > > > Cc: Igor Mammedov <imammedo at redhat.com> > > > > Cc: Paolo Bonzini <pbonzini at redhat.com> > > > > --- > > > > include/uapi/linux/vhost.h | 17 ++++++++++++++++- > > > > drivers/vhost/vhost.c | 5 +++++ > > > > 2 files changed, 21 insertions(+), 1 deletion(-) > > > > > > > > diff --git a/include/uapi/linux/vhost.h b/include/uapi/linux/vhost.h > > > > index ab373191..f71fa6d 100644 > > > > --- a/include/uapi/linux/vhost.h > > > > +++ b/include/uapi/linux/vhost.h > > > > @@ -80,7 +80,7 @@ struct vhost_memory { > > > > * Allows subsequent call to VHOST_OWNER_SET to succeed. */ > > > > #define VHOST_RESET_OWNER _IO(VHOST_VIRTIO, 0x02) > > > > > > > > -/* Set up/modify memory layout */ > > > > +/* Set up/modify memory layout: see also VHOST_GET_MEM_MAX_NREGIONS below. */ > > > > #define VHOST_SET_MEM_TABLE _IOW(VHOST_VIRTIO, 0x03, struct vhost_memory) > > > > > > > > /* Write logging setup. */ > > > > @@ -127,6 +127,21 @@ struct vhost_memory { > > > > /* Set eventfd to signal an error */ > > > > #define VHOST_SET_VRING_ERR _IOW(VHOST_VIRTIO, 0x22, struct vhost_vring_file) > > > > > > > > +/* Query upper limit on nregions in VHOST_SET_MEM_TABLE arguments. > > > > + * Returns: > > > > + * 0 < value <= MAX_INT - gives the upper limit, higher values will fail > > > > + * 0 - there's no static limit: try and see if it works > > > > + * -1 - on failure > > > > + */ > > > > +#define VHOST_GET_MEM_MAX_NREGIONS _IO(VHOST_VIRTIO, 0x23) > > > > + > > > > +/* Returned by VHOST_GET_MEM_MAX_NREGIONS to mean there's no static limit: > > > > + * try and it'll work if you are lucky. */ > > > > +#define VHOST_MEM_MAX_NREGIONS_NONE 0 > > > is it needed? we always have a limit, > > > or don't have IOCTL => -1 => old try and see way > > > > > > > +/* We support at least as many nregions in VHOST_SET_MEM_TABLE: > > > > + * for use on legacy kernels without VHOST_GET_MEM_MAX_NREGIONS support. */ > > > > +#define VHOST_MEM_MAX_NREGIONS_DEFAULT 64 > > > ^^^ not used below, > > > if it's for legacy then perhaps s/DEFAULT/LEGACY/ > > > > The assumption was that userspace detecting old kernels will just use 64, > > this means we do want a flag to get the old way. > > > > OTOH if you won't think it's useful, let me know. > this header will be synced into QEMU's tree so that we could use this define there, > isn't it? IMHO then _LEGACY is more exact description of macro. > > As for 0 return value, -1 is just fine for detecting old kernels (i.e. try and see if it works), so 0 looks unnecessary but it doesn't in any way hurt either. > For me limit or -1 is enough to try fix userspace.OK. Do you want to try now before I do v2?> > > > > > + > > > > /* VHOST_NET specific defines */ > > > > > > > > /* Attach virtio net ring to a raw socket, or tap device. > > > > diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c > > > > index 9e8e004..3b68f9d 100644 > > > > --- a/drivers/vhost/vhost.c > > > > +++ b/drivers/vhost/vhost.c > > > > @@ -917,6 +917,11 @@ long vhost_dev_ioctl(struct vhost_dev *d, unsigned int ioctl, void __user *argp) > > > > long r; > > > > int i, fd; > > > > > > > > + if (ioctl == VHOST_GET_MEM_MAX_NREGIONS) { > > > > + r = VHOST_MEMORY_MAX_NREGIONS; > > > > + goto done; > > > > + } > > > > + > > > > /* If you are not the owner, you can become one */ > > > > if (ioctl == VHOST_SET_OWNER) { > > > > r = vhost_dev_set_owner(d); > > -- > > To unsubscribe from this list: send the line "unsubscribe kvm" in > > the body of a message to majordomo at vger.kernel.org > > More majordomo info at http://vger.kernel.org/majordomo-info.html
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