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

["Michael S. Tsirkin" <mst@redhat.com>]

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@redhat.com>
> >
> > ---
> >
> >
> > 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;
> >  	}
> >  
> >   
> 
>