Re: [Qemu-devel] [PATCH V2 4/7] exec: allow to get a pointer for some mmio memory region

["Edgar E. Iglesias" <edgar.iglesias@gmail.com>]

On Fri, Feb 17, 2017 at 09:17:10PM +0100, fred.konrad@greensocs.com wrote:
> From: KONRAD Frederic <fred.konrad@greensocs.com>
> 
> This introduces a special callback which allows to run code from some MMIO
> devices.
> 
> SysBusDevice with a MemoryRegion which implements the request_ptr callback will
> be notified when the guest try to execute code from their offset. Then it will
> be able to eg: pre-load some code from an SPI device or ask a pointer from an
> external simulator, etc..
> 
> When the pointer or the data in it are no longer valid the device has to
> invalidate it.
> 
> Signed-off-by: KONRAD Frederic <fred.konrad@greensocs.com>
> 
> RFC -> V1:
>   * Use mmio-interface instead of directly creating the subregion.

Hi Fred,




> ---
>  cputlb.c              |  7 +++++++
>  include/exec/memory.h | 35 +++++++++++++++++++++++++++++++
>  memory.c              | 57 +++++++++++++++++++++++++++++++++++++++++++++++++++
>  3 files changed, 99 insertions(+)
> 
> diff --git a/cputlb.c b/cputlb.c
> index 846341e..9077247 100644
> --- a/cputlb.c
> +++ b/cputlb.c
> @@ -545,6 +545,13 @@ tb_page_addr_t get_page_addr_code(CPUArchState *env, target_ulong addr)
>      if (memory_region_is_unassigned(mr)) {
>          CPUClass *cc = CPU_GET_CLASS(cpu);
>  
> +        if (memory_region_request_mmio_ptr(mr, addr)) {
> +            /* A MemoryRegion is potentially added so re-run the
> +             * get_page_addr_code.
> +             */
> +            return get_page_addr_code(env, addr);
> +        }
> +
>          if (cc->do_unassigned_access) {
>              cc->do_unassigned_access(cpu, addr, false, true, 0, 4);
>          } else {
> diff --git a/include/exec/memory.h b/include/exec/memory.h
> index 987f925..36b0eec 100644
> --- a/include/exec/memory.h
> +++ b/include/exec/memory.h
> @@ -120,6 +120,15 @@ struct MemoryRegionOps {
>                                      uint64_t data,
>                                      unsigned size,
>                                      MemTxAttrs attrs);
> +    /* Instruction execution pre-callback:
> +     * @addr is the address of the access relative to the @mr.
> +     * @size is the size of the area returned by the callback.
> +     * @offset is the location of the pointer inside @mr.
> +     *
> +     * Returns a pointer to a location which contains guest code.
> +     */
> +    void *(*request_ptr)(void *opaque, hwaddr addr, unsigned *size,
> +                         unsigned *offset);
>  
>      enum device_endian endianness;
>      /* Guest-visible constraints: */
> @@ -1253,6 +1262,32 @@ void memory_global_dirty_log_stop(void);
>  void mtree_info(fprintf_function mon_printf, void *f, bool flatview);
>  
>  /**
> + * memory_region_request_mmio_ptr: request a pointer to an mmio
> + * MemoryRegion. If it is possible map a RAM MemoryRegion with this pointer.
> + * When the device wants to invalidate the pointer it will call
> + * memory_region_invalidate_mmio_ptr.
> + *
> + * @mr: #MemoryRegion to check
> + * @addr: address within that region
> + *
> + * Returns true on success, false otherwise.
> + */
> +bool memory_region_request_mmio_ptr(MemoryRegion *mr, hwaddr addr);
> +
> +/**
> + * memory_region_invalidate_mmio_ptr: invalidate the pointer to an mmio
> + * previously requested.
> + * In the end that means that if something wants to execute from this area it
> + * will need to request the pointer again.
> + *
> + * @mr: #MemoryRegion associated to the pointer.
> + * @addr: address within that region
> + * @size: size of that area.
> + */
> +void memory_region_invalidate_mmio_ptr(MemoryRegion *mr, hwaddr offset,
> +                                       unsigned size);
> +
> +/**
>   * memory_region_dispatch_read: perform a read directly to the specified
>   * MemoryRegion.
>   *
> diff --git a/memory.c b/memory.c
> index 6c58373..a605250 100644
> --- a/memory.c
> +++ b/memory.c
> @@ -30,6 +30,8 @@
>  #include "exec/ram_addr.h"
>  #include "sysemu/kvm.h"
>  #include "sysemu/sysemu.h"
> +#include "hw/misc/mmio_interface.h"
> +#include "hw/qdev-properties.h"
>  
>  //#define DEBUG_UNASSIGNED
>  
> @@ -2375,6 +2377,61 @@ void memory_listener_unregister(MemoryListener *listener)
>      QTAILQ_REMOVE(&listener->address_space->listeners, listener, link_as);
>  }
>  
> +bool memory_region_request_mmio_ptr(MemoryRegion *mr, hwaddr addr)
> +{
> +    void *host;
> +    unsigned size = 0;
> +    unsigned offset = 0;
> +    Object *new_interface;
> +
> +    if (!mr || !mr->ops->request_ptr) {
> +        return false;
> +    }
> +
> +    /*
> +     * Avoid an update if the request_ptr call
> +     * memory_region_invalidate_mmio_ptr which seems to be likely when we use
> +     * a cache.
> +     */
> +    memory_region_transaction_begin();
> +
> +    host = mr->ops->request_ptr(mr->opaque, addr - mr->addr, &size, &offset);
> +
> +    if (!host || !size) {
> +        memory_region_transaction_commit();
> +        return false;
> +    }
> +
> +    new_interface = object_new("mmio_interface");
> +    qdev_prop_set_uint64(DEVICE(new_interface), "start", offset);
> +    qdev_prop_set_uint64(DEVICE(new_interface), "end", offset + size - 1);
> +    qdev_prop_set_bit(DEVICE(new_interface), "ro", true);
> +    qdev_prop_set_ptr(DEVICE(new_interface), "host_ptr", host);
> +    qdev_prop_set_ptr(DEVICE(new_interface), "subregion", mr);
> +    object_property_set_bool(OBJECT(new_interface), true, "realized", NULL);
> +
> +    memory_region_transaction_commit();
> +    return true;
> +}
> +
> +void memory_region_invalidate_mmio_ptr(MemoryRegion *mr, hwaddr offset,
> +                                       unsigned size)
> +{
> +    MemoryRegionSection section = memory_region_find(mr, offset, size);
> +
> +    if (section.mr != mr) {
> +        /* memory_region_find add a ref on section.mr */
> +        memory_region_unref(section.mr);
> +        if (!MMIO_INTERFACE(section.mr->owner)) {

Is MMIO_INTERFACE defined yet?
This may break bisection...

Cheers,
Edgar


> +            return;
> +        }
> +        /* We found the interface just drop it. */
> +        object_property_set_bool(section.mr->owner, false, "realized", NULL);
> +        object_unref(section.mr->owner);
> +        object_unparent(section.mr->owner);
> +    }
> +}
> +
>  void address_space_init(AddressSpace *as, MemoryRegion *root, const char *name)
>  {
>      memory_region_ref(root);
> -- 
> 1.8.3.1
> 
>