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

Gregory Haskins
2007-04-05T14:58:39Z

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Hi Avi,

I have addressed your comments and re-attached the fixed up patch. Most of the things you suggested I implemented, but a few I didnt so I will comment inline...

>>> On Thu, Apr 5, 2007 at 3:07 AM, in message <4614A03C.2050707-atKUWr5tajBWk0Htik3J/w@public.gmane.org>,
Avi Kivity <avi-atKUWr5tajBWk0Htik3J/w@public.gmane.org> wrote:
> 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.

Done

>
>> + 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?

I believe Dor replied earlier stating the reason of being able to support holes. Another reason that I can think of that I particularly like about this design (which I am not claiming as my own) is that the device can relocate (e.g. LAPIC base addr) without worrying about reprogramming the bus.

>
>> +
>> + 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.

Done. Maximum # devices is currently 6, because anything beyond that and I think we need to revisit the linear alg ;)

>
>> +};
>> +
>> +/* 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
> */

Done

>
>> +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.

Done (though I hate lines that runneth over 80 ;)

>
>> +{
>> + INIT_LIST_HEAD(&bus- >list);
>> +}
>> +
>> +static inline struct kvm_io_device*
>>
>
> C style pointers:
> struct blah *somthing();

Done.

>
>> +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.

Done

>
>> +
>> + 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.

I am loath to make special cases if they can be avoided. I think performance wise a kvm_io_bus with one device wont be much different than having a special case check against apicbase. And the advantage that this buys us is future platforms (e.g. IA64?) may have more than one per-cpu MMIO address. I also realize that future platforms may be divergent from the entire in-kernel code base altogether, but I think the general and flexible way is better if there are no compromising tradeoffs, even if its only for example/reference. In this case I dont think there are any tradeoffs, so I left it. If you insist, I will pull it ;)

>
>> };
>>
>> 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

I believe I fixed this, but I am a little confused about what you were pointing out. The space is obvious. I believe you were pointing out that the braces weren't needed because its technically a single-line, and that the comment is fine. If I needed to change the comment too, let me know.

>
>> +
>> + 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.

Opps. Carry over from the apic branch merge. Fixed.

>
>>
>> - 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

Done

>
>> + 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.

I have confirmed that my 64 bit linux guest boots fine. I don't currently have any other guests. Careful review of the code leads me to believe this should be an inert change, so I wont go through the effort of finding an XP CD to install unless you insist ;)

Regards,
-Greg

[-- Attachment #2: in-kernel-mmio.patch --]
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diff --git a/drivers/kvm/kvm.h b/drivers/kvm/kvm.h
index fceeb84..c1923df 100644
--- a/drivers/kvm/kvm.h
+++ b/drivers/kvm/kvm.h
@@ -236,6 +236,56 @@ struct kvm_pio_request {
int rep;
};

+struct kvm_io_device {
+ unsigned long (*read)(struct kvm_io_device *this,
+ gpa_t addr,
+ int length);
+ void (*write)(struct kvm_io_device *this,
+ gpa_t addr,
+ int length,
+ unsigned long val);
+ int (*in_range)(struct kvm_io_device *this, gpa_t addr);
+
+ void *private;
+};
+
+/* 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.
+ */
+struct kvm_io_bus {
+ int dev_count;
+#define NR_IOBUS_DEVS 6
+ struct kvm_io_device *devs[NR_IOBUS_DEVS];
+};
+
+static inline void kvm_io_bus_init(struct kvm_io_bus *bus)
+{
+ memset(bus, 0, sizeof(*bus));
+}
+
+static inline struct kvm_io_device *kvm_io_bus_find_dev(struct kvm_io_bus *bus, gpa_t addr)
+{
+ int i;
+
+ for(i=0; i<bus->dev_count; i++) {
+ struct kvm_io_device *pos = bus->devs[i];
+
+ if (pos->in_range(pos, addr))
+ return pos;
+ }
+
+ return NULL;
+}
+
+static inline void kvm_io_bus_register_dev(struct kvm_io_bus *bus, struct kvm_io_device *dev)
+{
+ BUG_ON(bus->dev_count >= (NR_IOBUS_DEVS-1));
+
+ bus->devs[bus->dev_count++] = dev;
+}
+
struct kvm_vcpu {
struct kvm *kvm;
union {
@@ -294,6 +344,7 @@ 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 +396,7 @@ struct kvm {
unsigned long rmap_overflow;
struct list_head vm_list;
struct file *filp;
+ struct kvm_io_bus mmio_bus;
};

struct kvm_stat {
diff --git a/drivers/kvm/kvm_main.c b/drivers/kvm/kvm_main.c
index 4473174..9ca0ad3 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 +1017,28 @@ 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);
+
+ 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;
+ struct kvm_vcpu *vcpu = ctxt->vcpu;
+ struct kvm_io_device *mmio_dev;
+ gpa_t gpa;

if (vcpu->mmio_read_completed) {
memcpy(val, vcpu->mmio_data, bytes);
@@ -1029,18 +1047,24 @@ 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 X86EMUL_PROPAGATE_FAULT;

- return X86EMUL_UNHANDLEABLE;
+ /* Is this 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,
@@ -1068,8 +1092,9 @@ static int emulator_write_emulated(unsigned long addr,
unsigned int bytes,
struct x86_emulate_ctxt *ctxt)
{
- struct kvm_vcpu *vcpu = ctxt->vcpu;
- gpa_t gpa = vcpu->mmu.gva_to_gpa(vcpu, addr);
+ struct kvm_vcpu *vcpu = ctxt->vcpu;
+ struct kvm_io_device *mmio_dev;
+ gpa_t gpa = vcpu->mmu.gva_to_gpa(vcpu, addr);

if (gpa == UNMAPPED_GVA)
return X86EMUL_PROPAGATE_FAULT;
@@ -1077,6 +1102,13 @@ static int emulator_write_emulated(unsigned long addr,
if (emulator_write_phys(vcpu, gpa, val, bytes))
return X86EMUL_CONTINUE;

+ /* Is this MMIO handled locally? */
+ 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;

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