Re: [Qemu-devel] [RFC PATCH 3/3] KVM: s390: Hook up ioeventfds.

[Cornelia Huck]

On Thu, 21 Feb 2013 18:34:59 +0200
"Michael S. Tsirkin" <address@hidden> wrote:

> On Thu, Feb 21, 2013 at 04:21:43PM +0100, Cornelia Huck wrote:
> > On Thu, 21 Feb 2013 16:39:05 +0200
> > "Michael S. Tsirkin" <address@hidden> wrote:
> > 
> > > On Thu, Feb 21, 2013 at 02:13:00PM +0100, Cornelia Huck wrote:
> > > > As s390 doesn't use memory writes for virtio notifcations, create
> > > > a special kind of ioeventfd instead that hooks up into diagnose
> > > > 0x500 (kvm hypercall) with function code 3 (virtio-ccw notification).
> > > > 
> > > > Signed-off-by: Cornelia Huck <address@hidden>
> > > 
> > > Do we really have to put virtio specific stuff into kvm?
> > > How about we add generic functionality to match GPRs
> > > on a hypercall and signal an eventfd?
> > 
> > Worth a try implementing that.
> > 
> > > 
> > > Also, it's a bit unfortunate that this doesn't use
> > > the io bus datastructure, long term the linked list handling
> > > might become a bottleneck, using shared code this could maybe
> > > benefit from performance optimizations there.
> > 
> > The linked list stuff was more like an initial implementation that
> > could be improved later.
> > 
> > > io bus data structure currently has the ability to match on
> > > two 64 bit fields (addr/datamatch) and a signed 32 bit one (length).
> > > Isn't this sufficient for your purposes?
> > > How about sticking subchannel id in address, vq in data match
> > > and using io bus?
> > 
> > I can give that a try. (I must admit that I didn't look at the iobus
> > stuff in detail.)
> > 
> > > 
> > > BTW maybe we could do this for the user interface too,
> > > while I'm not 100% sure it's the cleanest thing to do
> > > (or will work), it would certainly minimize the patchset.
> > 
> > You mean integrating with the generic interface and dropping the new
> > ARCH flag?
> 
> Not sure about the flag but we could use the general structure
> without an arch-specific format, if that's a good fit.
> 
So I have something that seems to do what I want. I'll see if I can
morph it into something presentable tomorrow.

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..7fc195e 100644
--- a/arch/s390/kvm/diag.c
+++ b/arch/s390/kvm/diag.c
@@ -104,6 +104,20 @@ static int __diag_ipl_functions(struct kvm_vcpu *vcpu)
        return -EREMOTE;
 }
 
+static int __diag_virtio_hypercall(struct kvm_vcpu *vcpu)
+{
+       int ret, idx;
+       u64 vq = vcpu->run->s.regs.gprs[3];
+
+       idx = srcu_read_lock(&vcpu->kvm->srcu);
+       ret = kvm_io_bus_write(vcpu->kvm, KVM_CSS_BUS,
+                               vcpu->run->s.regs.gprs[2],
+                               vcpu->run->s.regs.gprs[1],
+                               &vq);
+       srcu_read_unlock(&vcpu->kvm->srcu, idx);
+       return ret;
+}
+
 int kvm_s390_handle_diag(struct kvm_vcpu *vcpu)
 {
        int code = (vcpu->arch.sie_block->ipb & 0xfff0000) >> 16;
@@ -118,6 +132,8 @@ int kvm_s390_handle_diag(struct kvm_vcpu *vcpu)
                return __diag_time_slice_end_directed(vcpu);
        case 0x308:
                return __diag_ipl_functions(vcpu);
+       case 0x500:
+               return __diag_virtio_hypercall(vcpu);
        default:
                return -EOPNOTSUPP;
        }
diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
index f822d36..04d2454 100644
--- a/arch/s390/kvm/kvm-s390.c
+++ b/arch/s390/kvm/kvm-s390.c
@@ -142,6 +142,7 @@ int kvm_dev_ioctl_check_extension(long ext)
        case KVM_CAP_ONE_REG:
        case KVM_CAP_ENABLE_CAP:
        case KVM_CAP_S390_CSS_SUPPORT:
+       case KVM_CAP_IOEVENTFD:
                r = 1;
                break;
        case KVM_CAP_NR_VCPUS:
diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index 3b768ef..59be516 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -148,6 +148,7 @@ struct kvm_io_bus {
 enum kvm_bus {
        KVM_MMIO_BUS,
        KVM_PIO_BUS,
+       KVM_CSS_BUS,
        KVM_NR_BUSES
 };
 
diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
index 9a2db57..1df0766 100644
--- a/include/uapi/linux/kvm.h
+++ b/include/uapi/linux/kvm.h
@@ -448,12 +448,14 @@ enum {
        kvm_ioeventfd_flag_nr_datamatch,
        kvm_ioeventfd_flag_nr_pio,
        kvm_ioeventfd_flag_nr_deassign,
+       kvm_ioeventfd_flag_nr_css,
        kvm_ioeventfd_flag_nr_max,
 };
 
 #define KVM_IOEVENTFD_FLAG_DATAMATCH (1 << kvm_ioeventfd_flag_nr_datamatch)
 #define KVM_IOEVENTFD_FLAG_PIO       (1 << kvm_ioeventfd_flag_nr_pio)
 #define KVM_IOEVENTFD_FLAG_DEASSIGN  (1 << kvm_ioeventfd_flag_nr_deassign)
+#define KVM_IOEVENTFD_FLAG_CSS       (1 << kvm_ioeventfd_flag_nr_css)
 
 #define KVM_IOEVENTFD_VALID_FLAG_MASK  ((1 << kvm_ioeventfd_flag_nr_max) - 1)
 
diff --git a/virt/kvm/eventfd.c b/virt/kvm/eventfd.c
index f0ced1a..57a06ff 100644
--- a/virt/kvm/eventfd.c
+++ b/virt/kvm/eventfd.c
@@ -576,6 +576,7 @@ struct _ioeventfd {
        u64                  datamatch;
        struct kvm_io_device dev;
        bool                 wildcard;
+       bool                 is_css;
 };
 
 static inline struct _ioeventfd *
@@ -607,24 +608,27 @@ ioeventfd_in_range(struct _ioeventfd *p, gpa_t addr, int 
len, const void *val)
 
        /* otherwise, we have to actually compare the data */
 
-       BUG_ON(!IS_ALIGNED((unsigned long)val, len));
-
-       switch (len) {
-       case 1:
-               _val = *(u8 *)val;
-               break;
-       case 2:
-               _val = *(u16 *)val;
-               break;
-       case 4:
-               _val = *(u32 *)val;
-               break;
-       case 8:
+       if (!p->is_css) {
+               BUG_ON(!IS_ALIGNED((unsigned long)val, len));
+
+               switch (len) {
+               case 1:
+                       _val = *(u8 *)val;
+                       break;
+               case 2:
+                       _val = *(u16 *)val;
+                       break;
+               case 4:
+                       _val = *(u32 *)val;
+                       break;
+               case 8:
+                       _val = *(u64 *)val;
+                       break;
+               default:
+                       return false;
+               }
+       } else
                _val = *(u64 *)val;
-               break;
-       default:
-               return false;
-       }
 
        return _val == p->datamatch ? true : false;
 }
@@ -679,25 +683,29 @@ static int
 kvm_assign_ioeventfd(struct kvm *kvm, struct kvm_ioeventfd *args)
 {
        int                       pio = args->flags & KVM_IOEVENTFD_FLAG_PIO;
-       enum kvm_bus              bus_idx = pio ? KVM_PIO_BUS : KVM_MMIO_BUS;
+       int                       css = args->flags & KVM_IOEVENTFD_FLAG_CSS;
+       enum kvm_bus              bus_idx;
        struct _ioeventfd        *p;
        struct eventfd_ctx       *eventfd;
        int                       ret;
 
-       /* must be natural-word sized */
-       switch (args->len) {
-       case 1:
-       case 2:
-       case 4:
-       case 8:
-               break;
-       default:
-               return -EINVAL;
-       }
+       bus_idx = pio ? KVM_PIO_BUS : css ? KVM_CSS_BUS: KVM_MMIO_BUS;
+       if (!css) {
+               /* must be natural-word sized */
+               switch (args->len) {
+               case 1:
+               case 2:
+               case 4:
+               case 8:
+                       break;
+               default:
+                       return -EINVAL;
+               }
 
-       /* check for range overflow */
-       if (args->addr + args->len < args->addr)
-               return -EINVAL;
+               /* check for range overflow */
+               if (args->addr + args->len < args->addr)
+                       return -EINVAL;
+       }
 
        /* check for extra flags that we don't understand */
        if (args->flags & ~KVM_IOEVENTFD_VALID_FLAG_MASK)
@@ -717,6 +725,7 @@ kvm_assign_ioeventfd(struct kvm *kvm, struct kvm_ioeventfd 
*args)
        p->addr    = args->addr;
        p->length  = args->len;
        p->eventfd = eventfd;
+       p->is_css  = css;
 
        /* The datamatch feature is optional, otherwise this is a wildcard */
        if (args->flags & KVM_IOEVENTFD_FLAG_DATAMATCH)
@@ -759,11 +768,13 @@ static int
 kvm_deassign_ioeventfd(struct kvm *kvm, struct kvm_ioeventfd *args)
 {
        int                       pio = args->flags & KVM_IOEVENTFD_FLAG_PIO;
-       enum kvm_bus              bus_idx = pio ? KVM_PIO_BUS : KVM_MMIO_BUS;
+       int                       css = args->flags & KVM_IOEVENTFD_FLAG_CSS;
+       enum kvm_bus              bus_idx;
        struct _ioeventfd        *p, *tmp;
        struct eventfd_ctx       *eventfd;
        int                       ret = -ENOENT;
 
+       bus_idx = pio ? KVM_PIO_BUS : css ? KVM_CSS_BUS: KVM_MMIO_BUS;
        eventfd = eventfd_ctx_fdget(args->fd);
        if (IS_ERR(eventfd))
                return PTR_ERR(eventfd);