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Re: [Qemu-devel] [PATCH v5 6/6] KVM: s390: Wire up ioeventfd.
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From: |
Michael S. Tsirkin |
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Subject: |
Re: [Qemu-devel] [PATCH v5 6/6] KVM: s390: Wire up ioeventfd. |
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Date: |
Tue, 5 Mar 2013 15:19:43 +0200 |
On Tue, Mar 05, 2013 at 09:13:08AM +0100, Cornelia Huck wrote:
> On Mon, 4 Mar 2013 21:07:41 -0300
> Marcelo Tosatti <address@hidden> wrote:
>
> > On Thu, Feb 28, 2013 at 12:33:21PM +0100, Cornelia Huck wrote:
> > > Enable ioeventfd support on s390 and hook up diagnose 500 virtio-ccw
> > > notifications.
> > >
> > > Signed-off-by: Cornelia Huck <address@hidden>
> > > ---
> > > arch/s390/kvm/Kconfig | 1 +
> > > arch/s390/kvm/Makefile | 2 +-
> > > arch/s390/kvm/diag.c | 26 ++++++++++++++++++++++++++
> > > arch/s390/kvm/kvm-s390.c | 1 +
> > > 4 files changed, 29 insertions(+), 1 deletion(-)
> > >
> > > diff --git a/arch/s390/kvm/Kconfig b/arch/s390/kvm/Kconfig
> > > index b58dd86..3c43e30 100644
> > > --- a/arch/s390/kvm/Kconfig
> > > +++ b/arch/s390/kvm/Kconfig
> > > @@ -22,6 +22,7 @@ config KVM
> > > select PREEMPT_NOTIFIERS
> > > select ANON_INODES
> > > select HAVE_KVM_CPU_RELAX_INTERCEPT
> > > + select HAVE_KVM_EVENTFD
> > > ---help---
> > > Support hosting paravirtualized guest machines using the SIE
> > > virtualization capability on the mainframe. This should work
> > > diff --git a/arch/s390/kvm/Makefile b/arch/s390/kvm/Makefile
> > > index 3975722..8fe9d65 100644
> > > --- a/arch/s390/kvm/Makefile
> > > +++ b/arch/s390/kvm/Makefile
> > > @@ -6,7 +6,7 @@
> > > # it under the terms of the GNU General Public License (version 2 only)
> > > # as published by the Free Software Foundation.
> > >
> > > -common-objs = $(addprefix ../../../virt/kvm/, kvm_main.o)
> > > +common-objs = $(addprefix ../../../virt/kvm/, kvm_main.o eventfd.o)
> > >
> > > ccflags-y := -Ivirt/kvm -Iarch/s390/kvm
> > >
> > > diff --git a/arch/s390/kvm/diag.c b/arch/s390/kvm/diag.c
> > > index a390687..1c01a99 100644
> > > --- a/arch/s390/kvm/diag.c
> > > +++ b/arch/s390/kvm/diag.c
> > > @@ -13,6 +13,7 @@
> > >
> > > #include <linux/kvm.h>
> > > #include <linux/kvm_host.h>
> > > +#include <asm/virtio-ccw.h>
> > > #include "kvm-s390.h"
> > > #include "trace.h"
> > > #include "trace-s390.h"
> > > @@ -104,6 +105,29 @@ static int __diag_ipl_functions(struct kvm_vcpu
> > > *vcpu)
> > > return -EREMOTE;
> > > }
> > >
> > > +static int __diag_virtio_hypercall(struct kvm_vcpu *vcpu)
> > > +{
> > > + int ret, idx;
> > > +
> > > + /* No virtio-ccw notification? Get out quickly. */
> > > + if (!vcpu->kvm->arch.css_support ||
> > > + (vcpu->run->s.regs.gprs[1] != KVM_S390_VIRTIO_CCW_NOTIFY))
> > > + return -EOPNOTSUPP;
> > > +
> > > + idx = srcu_read_lock(&vcpu->kvm->srcu);
> > > + /*
> > > + * The layout is as follows:
> > > + * - gpr 2 contains the subchannel id (passed as addr)
> > > + * - gpr 3 contains the virtqueue index (passed as datamatch)
> > > + */
> > > + ret = kvm_io_bus_write(vcpu->kvm, KVM_VIRTIO_CCW_NOTIFY_BUS,
> > > + vcpu->run->s.regs.gprs[2],
> > > + 8, &vcpu->run->s.regs.gprs[3]);
> > > + srcu_read_unlock(&vcpu->kvm->srcu, idx);
> > > + /* kvm_io_bus_write returns -EOPNOTSUPP if it found no match. */
> > > + return ret < 0 ? ret : 0;
> > > +}
> > > +
> >
> > What about the cookie?
>
> This is the not-performance-optimized version which went through our
> testing and which I'd like to see applied. I also have a not-yet-tested
> patch that adds cookie support (see below), but I'd like to postpone
> this to 3.10.
I agree it's best to delay this optimization, focus on basic
functionality now. As guest with cookie support is
compatible with host without said support (all we do
really is reserve a gpr), there won't be issues adding it later.
Some comments on the draft below.
> commit 8fce4a8a3478252f7ee2eb74d2732673f5911120
> Author: Cornelia Huck <address@hidden>
> Date: Tue Feb 26 17:05:01 2013 +0100
>
> virtio-ccw: ioeventfd: use cookies
>
> Signed-off-by: Cornelia Huck <address@hidden>
>
> diff --git a/arch/s390/kvm/diag.c b/arch/s390/kvm/diag.c
> index 1c01a99..bd2a013 100644
> --- a/arch/s390/kvm/diag.c
> +++ b/arch/s390/kvm/diag.c
> @@ -108,22 +108,29 @@ static int __diag_ipl_functions(struct kvm_vcpu *vcpu)
> static int __diag_virtio_hypercall(struct kvm_vcpu *vcpu)
> {
> int ret, idx;
> + long cookie;
>
> /* No virtio-ccw notification? Get out quickly. */
> if (!vcpu->kvm->arch.css_support ||
> (vcpu->run->s.regs.gprs[1] != KVM_S390_VIRTIO_CCW_NOTIFY))
> return -EOPNOTSUPP;
>
> + cookie = vcpu->run->s.regs.gprs[4];
Hmm signed so this can become negative.
> idx = srcu_read_lock(&vcpu->kvm->srcu);
> /*
> * The layout is as follows:
> * - gpr 2 contains the subchannel id (passed as addr)
> * - gpr 3 contains the virtqueue index (passed as datamatch)
> + * - gpr 4 contains the index on the bus (optionally)
> */
> - ret = kvm_io_bus_write(vcpu->kvm, KVM_VIRTIO_CCW_NOTIFY_BUS,
> - vcpu->run->s.regs.gprs[2],
> - 8, &vcpu->run->s.regs.gprs[3]);
> + ret = kvm_io_bus_write_cookie(vcpu->kvm, KVM_VIRTIO_CCW_NOTIFY_BUS,
> + vcpu->run->s.regs.gprs[2],
> + 8, &vcpu->run->s.regs.gprs[3],
> + &cookie);
> srcu_read_unlock(&vcpu->kvm->srcu, idx);
> + if (!ret)
> + /* Return cookie in gpr 2. */
> + vcpu->run->s.regs.gprs[2] = cookie;
We should also set gprs[2] to something sane if exiting to userspace
so avoid adding overhead for that case.
Probably # of devices + 1 or a negative value.
Are there 32 bit guests? If yes can they pass a negative value?
> /* kvm_io_bus_write returns -EOPNOTSUPP if it found no match. */
> return ret < 0 ? ret : 0;
> }
> diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> index 206247f..2f65a3a 100644
> --- a/include/linux/kvm_host.h
> +++ b/include/linux/kvm_host.h
> @@ -154,6 +154,8 @@ enum kvm_bus {
>
> int kvm_io_bus_write(struct kvm *kvm, enum kvm_bus bus_idx, gpa_t addr,
> int len, const void *val);
> +int kvm_io_bus_write_cookie(struct kvm *kvm, enum kvm_bus bus_idx, gpa_t
> addr,
> + int len, const void *val, long *cookie);
> int kvm_io_bus_read(struct kvm *kvm, enum kvm_bus bus_idx, gpa_t addr, int
> len,
> void *val);
> int kvm_io_bus_register_dev(struct kvm *kvm, enum kvm_bus bus_idx, gpa_t
> addr,
> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> index 7c188a3..b77ea5f 100644
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> @@ -2710,6 +2710,51 @@ int kvm_io_bus_write(struct kvm *kvm, enum kvm_bus
> bus_idx, gpa_t addr,
> return -EOPNOTSUPP;
> }
>
> +/* kvm_io_bus_write_cookie - called under kvm->slots_lock */
> +int kvm_io_bus_write_cookie(struct kvm *kvm, enum kvm_bus bus_idx, gpa_t
> addr,
> + int len, const void *val, long *cookie)
> +{
> + int idx, ret = -EOPNOTSUPP;
> + struct kvm_io_bus *bus;
> + struct kvm_io_range range;
> +
> + range = (struct kvm_io_range) {
> + .addr = addr,
> + .len = len,
> + };
> +
> + if (!cookie)
> + return -EINVAL;
> +
Hmm does this ever trigger?
> + bus = srcu_dereference(kvm->buses[bus_idx], &kvm->srcu);
> +
> + /* First try the device referenced by *cookie. */
> + if (kvm_io_bus_sort_cmp(&range, &bus->range[*cookie]) == 0)
We need to range-check the cookie.
> + if (!kvm_iodevice_write(bus->range[*cookie].dev, addr, len,
> + val))
> + return 0;
> +
> + /*
> + * *cookie contained garbage; fall back to search and return the
> + * correct value in *cookie.
> + */
> + idx = kvm_io_bus_get_first_dev(bus, addr, len);
> + if (idx < 0)
> + goto out;
> +
> + while (idx < bus->dev_count &&
> + kvm_io_bus_sort_cmp(&range, &bus->range[idx]) == 0) {
> + if (!kvm_iodevice_write(bus->range[idx].dev, addr, len, val)) {
> + ret = 0;
> + goto out;
> + }
> + idx++;
> + }
> +out:
> + *cookie = idx;
> + return ret;
> +}
> +
> /* kvm_io_bus_read - called under kvm->slots_lock */
> int kvm_io_bus_read(struct kvm *kvm, enum kvm_bus bus_idx, gpa_t addr,
> int len, void *val)