Re: [PATCH] Support for in-kernel mmio handlers

Avi Kivity
2007-04-05T07:07:40Z

Gregory Haskins wrote:
> The MMIO registration code has been broken out as a new patch from the in-kernel APIC work with the following changes per Avi's request:
>
> 1) Supports dynamic registration
> 2) Uses gpa_t addresses
> 3) Explicit per-cpu mappings
>
> In addition, I have added the concept of distinct VCPU and VM level registrations (where VCPU devices will eclipse competing VM registrations (if any). This will be key down the road where LAPICs should use VCPU registration, but IOAPICs should use VM level.
>
> Signed-off-by: Gregory Haskins <ghaskins-Et1tbQHTxzrQT0dZR+AlfA@public.gmane.org>
>
> ---
> drivers/kvm/kvm.h | 50 +++++++++++++++++++++++++++++++++++++++++++++
> drivers/kvm/kvm_main.c | 53 +++++++++++++++++++++++++++++++++++++++--------
> 2 files changed, 94 insertions(+), 9 deletions(-)
>
> diff --git a/drivers/kvm/kvm.h b/drivers/kvm/kvm.h
> index fceeb84..3334730 100644
> --- a/drivers/kvm/kvm.h
> +++ b/drivers/kvm/kvm.h
> @@ -236,6 +236,54 @@ struct kvm_pio_request {
> int rep;
> };
>
> +struct kvm_io_device {
> + unsigned long (*read)(struct kvm_io_device *this,
> + gpa_t addr,
> + unsigned long length);
> + void (*write)(struct kvm_io_device *this,
> + gpa_t addr,
> + unsigned long length,
> + unsigned long val);
>

length could be just an int.

> + int (*in_range)(struct kvm_io_device *this, gpa_t addr);
>

Do you see any reason to have this as a callback and not a pair of gpas?

> +
> + void *private;
> + struct list_head link;
>

Having these in an array would be much more efficient. A fixed size
array of moderate size should suffice.

> +};
> +
> +/* It would be nice to use something smarter than a linear search, TBD...
> + Thankfully we dont expect many devices to register (famous last words :),
> + so until then it will suffice. At least its abstracted so we can change
> + in one place.
> + */
>

/*
* kernel comments look
* like this
*/

> +struct kvm_io_bus {
> + struct list_head list;
> +};
> +
> +static inline void
> +kvm_io_bus_init(struct kvm_io_bus *bus)
>

function declarations on one line please.

> +{
> + INIT_LIST_HEAD(&bus->list);
> +}
> +
> +static inline struct kvm_io_device*
>

C style pointers:
struct blah *somthing();

> +kvm_io_bus_find_dev(struct kvm_io_bus *bus, gpa_t addr)
> +{
> + struct kvm_io_device *pos = NULL;
> +
> + list_for_each_entry(pos, &bus->list, link) {
> + if(pos->in_range(pos, addr))
> + return pos;
> + }
>

space after if. avoid redundant {}. Have Documentaion/CodingStyle
tattooed somewhere easily accessible.

> +
> + return NULL;
> +}
> +
> +static inline void
> +kvm_io_bus_register_dev(struct kvm_io_bus *bus, struct kvm_io_device *dev)
> +{
> + list_add_tail(&dev->link, &bus->list);
> +}
> +
> struct kvm_vcpu {
> struct kvm *kvm;
> union {
> @@ -294,6 +342,7 @@ struct kvm_vcpu {
> gpa_t mmio_phys_addr;
> struct kvm_pio_request pio;
> void *pio_data;
> + struct kvm_io_bus mmio_bus;
>
> int sigset_active;
> sigset_t sigset;
> @@ -345,6 +394,7 @@ struct kvm {
> unsigned long rmap_overflow;
> struct list_head vm_list;
> struct file *filp;
> + struct kvm_io_bus mmio_bus;
>

The per-vcpu I/O bus is special in that it has exactly one component,
and one which can change its address. I think we can special case it
and just check for apic addresses explicitly when searching the bus.

> };
>
> struct kvm_stat {
> diff --git a/drivers/kvm/kvm_main.c b/drivers/kvm/kvm_main.c
> index 4473174..da119c0 100644
> --- a/drivers/kvm/kvm_main.c
> +++ b/drivers/kvm/kvm_main.c
> @@ -294,6 +294,7 @@ static struct kvm *kvm_create_vm(void)
>
> spin_lock_init(&kvm->lock);
> INIT_LIST_HEAD(&kvm->active_mmu_pages);
> + kvm_io_bus_init(&kvm->mmio_bus);
> for (i = 0; i < KVM_MAX_VCPUS; ++i) {
> struct kvm_vcpu *vcpu = &kvm->vcpus[i];
>
> @@ -302,6 +303,7 @@ static struct kvm *kvm_create_vm(void)
> vcpu->kvm = kvm;
> vcpu->mmu.root_hpa = INVALID_PAGE;
> INIT_LIST_HEAD(&vcpu->free_pages);
> + kvm_io_bus_init(&vcpu->mmio_bus);
> spin_lock(&kvm_lock);
> list_add(&kvm->vm_list, &vm_list);
> spin_unlock(&kvm_lock);
> @@ -1015,12 +1017,30 @@ static int emulator_write_std(unsigned long addr,
> return X86EMUL_UNHANDLEABLE;
> }
>
> +static struct kvm_io_device* vcpu_find_mmio_dev(struct kvm_vcpu *vcpu,
> + gpa_t addr)
> +{
> + struct kvm_io_device *mmio_dev;
> +
> + /* First check the local CPU addresses */
> + mmio_dev = kvm_io_bus_find_dev(&vcpu->mmio_bus, addr);
> + if(!mmio_dev) {
> + /* Then check the entire VM */
> + mmio_dev = kvm_io_bus_find_dev(&vcpu->kvm->mmio_bus, addr);
> + }
>

space, comment, braces

> +
> + return mmio_dev;
> +}
> +
> static int emulator_read_emulated(unsigned long addr,
> unsigned long *val,
> unsigned int bytes,
> struct x86_emulate_ctxt *ctxt)
> {
> struct kvm_vcpu *vcpu = ctxt->vcpu;
> + gpa_t gpa;
> + int i;
> + struct kvm_io_device *mmio_dev;
>
> if (vcpu->mmio_read_completed) {
> memcpy(val, vcpu->mmio_data, bytes);
> @@ -1029,18 +1049,24 @@ static int emulator_read_emulated(unsigned long addr,
> } else if (emulator_read_std(addr, val, bytes, ctxt)
> == X86EMUL_CONTINUE)
> return X86EMUL_CONTINUE;
> - else {
> - gpa_t gpa = vcpu->mmu.gva_to_gpa(vcpu, addr);
>
> - if (gpa == UNMAPPED_GVA)
> - return X86EMUL_PROPAGATE_FAULT;
> - vcpu->mmio_needed = 1;
> - vcpu->mmio_phys_addr = gpa;
> - vcpu->mmio_size = bytes;
> - vcpu->mmio_is_write = 0;
> + gpa = vcpu->mmu.gva_to_gpa(vcpu, addr);
> + if (gpa == UNMAPPED_GVA)
> + return vcpu_printf(vcpu, "not present\n"), X86EMUL_PROPAGATE_FAULT;
>

The vcpu_printf() snuck in somehow.

>
> - return X86EMUL_UNHANDLEABLE;
> + /* Is thie MMIO handled locally? */
> + mmio_dev = vcpu_find_mmio_dev(vcpu, gpa);
> + if(mmio_dev) {
> + *val = mmio_dev->read(mmio_dev, gpa, bytes);
> + return X86EMUL_CONTINUE;
> }
> +
> + vcpu->mmio_needed = 1;
> + vcpu->mmio_phys_addr = gpa;
> + vcpu->mmio_size = bytes;
> + vcpu->mmio_is_write = 0;
> +
> + return X86EMUL_UNHANDLEABLE;
> }
>
> static int emulator_write_phys(struct kvm_vcpu *vcpu, gpa_t gpa,
> @@ -1070,6 +1096,8 @@ static int emulator_write_emulated(unsigned long addr,
> {
> struct kvm_vcpu *vcpu = ctxt->vcpu;
> gpa_t gpa = vcpu->mmu.gva_to_gpa(vcpu, addr);
> + int i;
> + struct kvm_io_device *mmio_dev;
>
> if (gpa == UNMAPPED_GVA)
> return X86EMUL_PROPAGATE_FAULT;
> @@ -1077,6 +1105,13 @@ static int emulator_write_emulated(unsigned long addr,
> if (emulator_write_phys(vcpu, gpa, val, bytes))
> return X86EMUL_CONTINUE;
>
> + /* Is thie MMIO handled locally? */
>

spelling

> + mmio_dev = vcpu_find_mmio_dev(vcpu, gpa);
> + if(mmio_dev) {
> + mmio_dev->write(mmio_dev, gpa, bytes, val);
> + return X86EMUL_CONTINUE;
> + }
> +
> vcpu->mmio_needed = 1;
> vcpu->mmio_phys_addr = gpa;
> vcpu->mmio_size = bytes;
>
>
>

Please fix and *test*. Boot at least 32-bit Windows with ACPI HAL and
64-bit Linux, the more the better of course.

--
Do not meddle in the internals of kernels, for they are subtle and quick to panic.