Re: [PATCH RFC] pass write value to in_range pointers

From: Michael S. Tsirkin
Date: Mon Jun 22 2009 - 12:09:24 EST

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On Mon, Jun 22, 2009 at 11:45:00AM -0400, Gregory Haskins wrote:
> Michael S. Tsirkin wrote:
> > It seems that a lot of complexity and trickiness with iosignalfd is
> > handling the group/item relationship, which comes about because kvm does
> > not currently let a device on the bus claim a write transaction based on the
> > value written. This could be greatly simplified if the value written
> > was passed to the in_range check for write operation. We could then
> > simply make each kvm_iosignalfd a device on the bus.
> >
> > What does everyone think of the following lightly tested patch?
> >
>
> Hi Michael,
> Its interesting, but I am not convinced its necessary. We created the
> group/item layout because iosignalfds are unique in that they are
> probably the only IO device that wants to do some kind of address
> aliasing.

We actually already have aliasing: is_write flag is used for this
purpose. Actually, it's possible to remove is_write by passing
a null pointer in write_val for reads. I like this a bit less as
the code generated is less compact ... Avi, what do you think?

> With what you are proposing here, you are adding aliasing
> support to the general infrastructure which I am not (yet) convinced is
> necessary.

Infrastructure is a big name for something that adds a total of 10 lines to kvm.
And it should at least halve the size of your 450-line patch.

> If there isn't a use case for other devices to have
> aliasing, I would think the logic is best contained in iosignalfd. Do
> you have something in mind?

One is enough :)
Seriously, do you see that this saves you all of RCU, linked lists and
counters? You don't need to keep track of iofds, you don't need to
implement your own lookup logic - you just use the kvm device
and that's it.

> Kind Regards,
> -Greg
>
> > -->
> >
> > Subject: kvm: pass value to in_range callback
> >
> > For write transactions, pass the value written to in_range checks so
> > that we can make each iosignalfd a separate device on kvm bus.
> >
> > Signed-off-by: Michael S. Tsirkin <mst@xxxxxxxxxx>
> >
> > ---
> >
> >
> > diff --git a/virt/kvm/iodev.h b/virt/kvm/iodev.h
> > index 55e8846..98a25af 100644
> > --- a/virt/kvm/iodev.h
> > +++ b/virt/kvm/iodev.h
> > @@ -28,7 +28,7 @@ struct kvm_io_device {
> > int len,
> > const void *val);
> > int (*in_range)(struct kvm_io_device *this, gpa_t addr, int len,
> > - int is_write);
> > + int is_write, void *write_val);
> > void (*destructor)(struct kvm_io_device *this);
> >
> > void *private;
> > @@ -51,9 +51,10 @@ static inline void kvm_iodevice_write(struct kvm_io_device *dev,
> > }
> >
> > static inline int kvm_iodevice_inrange(struct kvm_io_device *dev,
> > - gpa_t addr, int len, int is_write)
> > + gpa_t addr, int len, int is_write,
> > + void *write_val)
> > {
> > - return dev->in_range(dev, addr, len, is_write);
> > + return dev->in_range(dev, addr, len, is_write, write_val);
> > }
> >
> > static inline void kvm_iodevice_destructor(struct kvm_io_device *dev)
> > diff --git a/arch/ia64/kvm/kvm-ia64.c b/arch/ia64/kvm/kvm-ia64.c
> > index 80c57b0..8cfdf9d 100644
> > --- a/arch/ia64/kvm/kvm-ia64.c
> > +++ b/arch/ia64/kvm/kvm-ia64.c
> > @@ -211,11 +211,13 @@ int kvm_dev_ioctl_check_extension(long ext)
> > }
> >
> > static struct kvm_io_device *vcpu_find_mmio_dev(struct kvm_vcpu *vcpu,
> > - gpa_t addr, int len, int is_write)
> > + gpa_t addr, int len, int is_write,
> > + void *write_val)
> > {
> > struct kvm_io_device *dev;
> >
> > - dev = kvm_io_bus_find_dev(&vcpu->kvm->mmio_bus, addr, len, is_write);
> > + dev = kvm_io_bus_find_dev(&vcpu->kvm->mmio_bus, addr, len, is_write,
> > + write_val);
> >
> > return dev;
> > }
> > @@ -247,7 +247,8 @@ static int handle_mmio(struct kvm_vcpu *vcpu, struct kvm_run *kvm_run)
> > kvm_run->exit_reason = KVM_EXIT_MMIO;
> > return 0;
> > mmio:
> > - mmio_dev = vcpu_find_mmio_dev(vcpu, p->addr, p->size, !p->dir);
> > + mmio_dev = vcpu_find_mmio_dev(vcpu, p->addr, p->size,
> > + !p->dir, &p->data);
> > if (mmio_dev) {
> > if (!p->dir)
> > kvm_iodevice_write(mmio_dev, p->addr, p->size,
> > diff --git a/arch/x86/kvm/i8254.c b/arch/x86/kvm/i8254.c
> > index 4d6f0d2..5ba21ff 100644
> > --- a/arch/x86/kvm/i8254.c
> > +++ b/arch/x86/kvm/i8254.c
> > @@ -485,7 +485,7 @@ static void pit_ioport_read(struct kvm_io_device *this,
> > }
> >
> > static int pit_in_range(struct kvm_io_device *this, gpa_t addr,
> > - int len, int is_write)
> > + int len, int is_write, void *write_val)
> > {
> > return ((addr >= KVM_PIT_BASE_ADDRESS) &&
> > (addr < KVM_PIT_BASE_ADDRESS + KVM_PIT_MEM_LENGTH));
> > diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
> > index ae99d83..456fd53 100644
> > --- a/arch/x86/kvm/lapic.c
> > +++ b/arch/x86/kvm/lapic.c
> > @@ -721,7 +721,7 @@ static void apic_mmio_write(struct kvm_io_device *this,
> > }
> >
> > static int apic_mmio_range(struct kvm_io_device *this, gpa_t addr,
> > - int len, int size)
> > + int len, int is_write, void *write_val)
> > {
> > struct kvm_lapic *apic = (struct kvm_lapic *)this->private;
> > int ret = 0;
> > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> > index 249540f..9d29017 100644
> > --- a/arch/x86/kvm/x86.c
> > +++ b/arch/x86/kvm/x86.c
> > @@ -2043,13 +2043,13 @@ static void kvm_init_msr_list(void)
> > */
> > static struct kvm_io_device *vcpu_find_pervcpu_dev(struct kvm_vcpu *vcpu,
> > gpa_t addr, int len,
> > - int is_write)
> > + int is_write, void *write_val)
> > {
> > struct kvm_io_device *dev;
> >
> > if (vcpu->arch.apic) {
> > dev = &vcpu->arch.apic->dev;
> > - if (dev->in_range(dev, addr, len, is_write))
> > + if (dev->in_range(dev, addr, len, is_write, write_val))
> > return dev;
> > }
> > return NULL;
> > @@ -2058,14 +2058,14 @@ static struct kvm_io_device *vcpu_find_pervcpu_dev(struct kvm_vcpu *vcpu,
> >
> > static struct kvm_io_device *vcpu_find_mmio_dev(struct kvm_vcpu *vcpu,
> > gpa_t addr, int len,
> > - int is_write)
> > + int is_write, void *write_val)
> > {
> > struct kvm_io_device *dev;
> >
> > - dev = vcpu_find_pervcpu_dev(vcpu, addr, len, is_write);
> > + dev = vcpu_find_pervcpu_dev(vcpu, addr, len, is_write, write_val);
> > if (dev == NULL)
> > dev = kvm_io_bus_find_dev(&vcpu->kvm->mmio_bus, addr, len,
> > - is_write);
> > + is_write, write_val);
> > return dev;
> > }
> >
> > @@ -2161,7 +2161,7 @@ mmio:
> > * Is this MMIO handled locally?
> > */
> > mutex_lock(&vcpu->kvm->lock);
> > - mmio_dev = vcpu_find_mmio_dev(vcpu, gpa, bytes, 0);
> > + mmio_dev = vcpu_find_mmio_dev(vcpu, gpa, bytes, 0, NULL);
> > if (mmio_dev) {
> > kvm_iodevice_read(mmio_dev, gpa, bytes, val);
> > mutex_unlock(&vcpu->kvm->lock);
> > @@ -2216,7 +2216,7 @@ mmio:
> > * Is this MMIO handled locally?
> > */
> > mutex_lock(&vcpu->kvm->lock);
> > - mmio_dev = vcpu_find_mmio_dev(vcpu, gpa, bytes, 1);
> > + mmio_dev = vcpu_find_mmio_dev(vcpu, gpa, bytes, 1, val);
> > if (mmio_dev) {
> > kvm_iodevice_write(mmio_dev, gpa, bytes, val);
> > mutex_unlock(&vcpu->kvm->lock);
> > @@ -2576,9 +2576,10 @@ static void pio_string_write(struct kvm_io_device *pio_dev,
> >
> > static struct kvm_io_device *vcpu_find_pio_dev(struct kvm_vcpu *vcpu,
> > gpa_t addr, int len,
> > - int is_write)
> > + int is_write, void *write_val)
> > {
> > - return kvm_io_bus_find_dev(&vcpu->kvm->pio_bus, addr, len, is_write);
> > + return kvm_io_bus_find_dev(&vcpu->kvm->pio_bus, addr, len, is_write,
> > + write_val);
> > }
> >
> > int kvm_emulate_pio(struct kvm_vcpu *vcpu, struct kvm_run *run, int in,
> > @@ -2608,7 +2608,8 @@ int kvm_emulate_pio(struct kvm_vcpu *vcpu, struct kvm_run *run, int in,
> > val = kvm_register_read(vcpu, VCPU_REGS_RAX);
> > memcpy(vcpu->arch.pio_data, &val, 4);
> >
> > - pio_dev = vcpu_find_pio_dev(vcpu, port, size, !in);
> > + pio_dev = vcpu_find_pio_dev(vcpu, port, size, !in,
> > + vcpu->arch.pio_data);
> > if (pio_dev) {
> > kernel_pio(pio_dev, vcpu, vcpu->arch.pio_data);
> > complete_pio(vcpu);
> > @@ -2624,7 +2625,6 @@ int kvm_emulate_pio_string(struct kvm_vcpu *vcpu, struct kvm_run *run, int in,
> > {
> > unsigned now, in_page;
> > int ret = 0;
> > - struct kvm_io_device *pio_dev;
> >
> > vcpu->run->exit_reason = KVM_EXIT_IO;
> > vcpu->run->io.direction = in ? KVM_EXIT_IO_IN : KVM_EXIT_IO_OUT;
> > @@ -2672,9 +2672,6 @@ int kvm_emulate_pio_string(struct kvm_vcpu *vcpu, struct kvm_run *run, int in,
> >
> > vcpu->arch.pio.guest_gva = address;
> >
> > - pio_dev = vcpu_find_pio_dev(vcpu, port,
> > - vcpu->arch.pio.cur_count,
> > - !vcpu->arch.pio.in);
> > if (!vcpu->arch.pio.in) {
> > /* string PIO write */
> > ret = pio_copy_data(vcpu);
> > @@ -2682,13 +2679,20 @@ int kvm_emulate_pio_string(struct kvm_vcpu *vcpu, struct kvm_run *run, int in,
> > kvm_inject_gp(vcpu, 0);
> > return 1;
> > }
> > - if (ret == 0 && pio_dev) {
> > - pio_string_write(pio_dev, vcpu);
> > - complete_pio(vcpu);
> > - if (vcpu->arch.pio.count == 0)
> > - ret = 1;
> > + if (ret == 0) {
> > + struct kvm_io_device *pio_dev;
> > + pio_dev = vcpu_find_pio_dev(vcpu, port,
> > + vcpu->arch.pio.cur_count,
> > + 1, vcpu->arch.pio_data);
> > + if (pio_dev) {
> > + pio_string_write(pio_dev, vcpu);
> > + complete_pio(vcpu);
> > + if (vcpu->arch.pio.count == 0)
> > + ret = 1;
> > + }
> > }
> > - } else if (pio_dev)
> > + } else if (vcpu_find_pio_dev(vcpu, port, vcpu->arch.pio.cur_count, 0,
> > + NULL))
> > pr_unimpl(vcpu, "no string pio read support yet, "
> > "port %x size %d count %ld\n",
> > port, size, count);
> > diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> > index aacc544..0fb7938 100644
> > --- a/include/linux/kvm_host.h
> > +++ b/include/linux/kvm_host.h
> > @@ -60,7 +60,8 @@ struct kvm_io_bus {
> > void kvm_io_bus_init(struct kvm_io_bus *bus);
> > void kvm_io_bus_destroy(struct kvm_io_bus *bus);
> > struct kvm_io_device *kvm_io_bus_find_dev(struct kvm_io_bus *bus,
> > - gpa_t addr, int len, int is_write);
> > + gpa_t addr, int len, int is_write,
> > + void *write_val);
> > void kvm_io_bus_register_dev(struct kvm_io_bus *bus,
> > struct kvm_io_device *dev);
> >
> > diff --git a/virt/kvm/coalesced_mmio.c b/virt/kvm/coalesced_mmio.c
> > index 5ae620d..3a1cbfd 100644
> > --- a/virt/kvm/coalesced_mmio.c
> > +++ b/virt/kvm/coalesced_mmio.c
> > @@ -15,7 +15,8 @@
> > #include "coalesced_mmio.h"
> >
> > static int coalesced_mmio_in_range(struct kvm_io_device *this,
> > - gpa_t addr, int len, int is_write)
> > + gpa_t addr, int len, int is_write,
> > + void *write_val)
> > {
> > struct kvm_coalesced_mmio_dev *dev =
> > (struct kvm_coalesced_mmio_dev*)this->private;
> > diff --git a/virt/kvm/ioapic.c b/virt/kvm/ioapic.c
> > index 1eddae9..2adbb1b 100644
> > --- a/virt/kvm/ioapic.c
> > +++ b/virt/kvm/ioapic.c
> > @@ -221,7 +221,8 @@ void kvm_ioapic_update_eoi(struct kvm *kvm, int vector, int trigger_mode)
> > }
> >
> > static int ioapic_in_range(struct kvm_io_device *this, gpa_t addr,
> > - int len, int is_write)
> > + int len, int is_write,
> > + void *write_val)
> > {
> > struct kvm_ioapic *ioapic = (struct kvm_ioapic *)this->private;
> >
> > diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> > index 7645543..b97e390 100644
> > --- a/virt/kvm/kvm_main.c
> > +++ b/virt/kvm/kvm_main.c
> > @@ -2445,14 +2445,15 @@ void kvm_io_bus_destroy(struct kvm_io_bus *bus)
> > }
> >
> > struct kvm_io_device *kvm_io_bus_find_dev(struct kvm_io_bus *bus,
> > - gpa_t addr, int len, int is_write)
> > + gpa_t addr, int len, int is_write,
> > + void *write_val)
> > {
> > int i;
> >
> > for (i = 0; i < bus->dev_count; i++) {
> > struct kvm_io_device *pos = bus->devs[i];
> >
> > - if (pos->in_range(pos, addr, len, is_write))
> > + if (pos->in_range(pos, addr, len, is_write, write_val))
> > return pos;
> > }
> >
> >
>
>

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