Re: [Qemu-devel] [PATCH RFC v2 2/2] hw/pci: handle unassigned pci addresses

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

On Mon, Sep 09, 2013 at 02:11:54PM +0300, Marcel Apfelbaum wrote:
> Created a MemoryRegion with negative priority that
> spans over all the pci address space.
> It "intercepts" the accesses to unassigned pci
> address space and will follow the pci spec:
>  1. returns -1 on read
>  2. does nothing on write
>  3. sets the RECEIVED MASTER ABORT bit in the STATUS register
>     of the device that initiated the transaction
> 
> Note: This implementation assumes that all the reads/writes to
> the pci address space are done by the cpu.
> 
> Signed-off-by: Marcel Apfelbaum <marcel.a@redhat.com>
> ---
> Changes from v1:
>  - "pci-unassigned-mem" MemoryRegion resides now in PCIBus and not on
>     various Host Bridges
>  - "pci-unassgined-mem" does not have a ".valid.accept" field and
>     implements read write methods
> 
>  hw/pci/pci.c             | 46 ++++++++++++++++++++++++++++++++++++++++++++++
>  include/hw/pci/pci_bus.h |  1 +
>  2 files changed, 47 insertions(+)
> 
> diff --git a/hw/pci/pci.c b/hw/pci/pci.c
> index d00682e..b6a8026 100644
> --- a/hw/pci/pci.c
> +++ b/hw/pci/pci.c
> @@ -283,6 +283,43 @@ const char *pci_root_bus_path(PCIDevice *dev)
>      return rootbus->qbus.name;
>  }
>  
> +static void unassigned_mem_access(PCIBus *bus)
> +{
> +    /* FIXME assumption: memory access to the pci address
> +     * space is always initiated by the host bridge

/* Always
 * like
 * this
 */

/* Not
 * like this */

> +     * (device 0 on the bus) */

Can't we pass the master device in?
We are still left with the assumption that
there's a single master, but at least
we get rid of the assumption that it's
always device 0 function 0.


> +    PCIDevice *d = bus->devices[0];
> +    if (!d) {
> +        return;
> +    }
> +
> +    pci_word_test_and_set_mask(d->config + PCI_STATUS,
> +                               PCI_STATUS_REC_MASTER_ABORT);

Probably should check and set secondary status for
a bridge device.

> +}
> +
> +static uint64_t unassigned_mem_read(void *opaque, hwaddr addr, unsigned size)
> +{
> +    PCIBus *bus = opaque;
> +    unassigned_mem_access(bus);
> +
> +    return -1ULL;
> +}
> +
> +static void unassigned_mem_write(void *opaque, hwaddr addr, uint64_t val,
> +                                unsigned size)
> +{
> +    PCIBus *bus = opaque;
> +    unassigned_mem_access(bus);
> +}
> +
> +static const MemoryRegionOps unassigned_mem_ops = {
> +    .read = unassigned_mem_read,
> +    .write = unassigned_mem_write,
> +    .endianness = DEVICE_NATIVE_ENDIAN,
> +};
> +
> +#define UNASSIGNED_MEM_PRIORITY -1
> +
>  static void pci_bus_init(PCIBus *bus, DeviceState *parent,
>                           const char *name,
>                           MemoryRegion *address_space_mem,


I would rename "unassigned" to "pci_master_Abort_" everywhere.

Call things by what they do not how they are used.

> @@ -294,6 +331,15 @@ static void pci_bus_init(PCIBus *bus, DeviceState *parent,
>      bus->address_space_mem = address_space_mem;
>      bus->address_space_io = address_space_io;
>  
> +
> +    memory_region_init_io(&bus->unassigned_mem, OBJECT(bus),
> +                          &unassigned_mem_ops, bus, "pci-unassigned",
> +                          memory_region_size(bus->address_space_mem));
> +    memory_region_add_subregion_overlap(bus->address_space_mem,
> +                                        bus->address_space_mem->addr,
> +                                        &bus->unassigned_mem,
> +                                        UNASSIGNED_MEM_PRIORITY);
> +
>      /* host bridge */
>      QLIST_INIT(&bus->child);
>

It seems safer to add an API for enabling this functionality.
Something like

pci_set_master_for_master_abort(PCIBus *, PCIDevice *);

  
> diff --git a/include/hw/pci/pci_bus.h b/include/hw/pci/pci_bus.h
> index 9df1788..4cc25a3 100644
> --- a/include/hw/pci/pci_bus.h
> +++ b/include/hw/pci/pci_bus.h
> @@ -23,6 +23,7 @@ struct PCIBus {
>      PCIDevice *parent_dev;
>      MemoryRegion *address_space_mem;
>      MemoryRegion *address_space_io;
> +    MemoryRegion unassigned_mem;
>  
>      QLIST_HEAD(, PCIBus) child; /* this will be replaced by qdev later */
>      QLIST_ENTRY(PCIBus) sibling;/* this will be replaced by qdev later */
> -- 
> 1.8.3.1