Re: [Qemu-devel] [RE-RESEND PATCH] pci: Adjust PCI config limit based on bus topology

[Marcel Apfelbaum <marcel.apfelbaum@gmail.com>]

On 01/19/2016 01:06 AM, Alex Williamson wrote:
> A conventional PCI bus does not support config space accesses above
> the standard 256 byte configuration space.  PCIe-to-PCI bridges are
> not permitted to forward transactions if the extended register address
> field is non-zero and must handle it as an unsupported request (PCIe
> bridge spec rev 1.0, 4.1.3, 4.1.4).  Therefore, we should not support
> extended config space if there is a conventional bus anywhere on the
> path to a device.
>
> Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
> ---
> Previous postings:
> https://lists.gnu.org/archive/html/qemu-devel/2015-10/msg05384.html
> https://lists.gnu.org/archive/html/qemu-devel/2015-11/msg02422.html
>
>   hw/pci/pci_host.c |   26 ++++++++++++++++++++++++++
>   1 file changed, 26 insertions(+)
>
> diff --git a/hw/pci/pci_host.c b/hw/pci/pci_host.c
> index 49f59a5..3a3e294 100644
> --- a/hw/pci/pci_host.c
> +++ b/hw/pci/pci_host.c
> @@ -19,6 +19,7 @@
>    */
>
>   #include "hw/pci/pci.h"
> +#include "hw/pci/pci_bridge.h"
>   #include "hw/pci/pci_host.h"
>   #include "hw/pci/pci_bus.h"
>   #include "trace.h"
> @@ -49,9 +50,29 @@ static inline PCIDevice *pci_dev_find_by_addr(PCIBus *bus, uint32_t addr)
>       return pci_find_device(bus, bus_num, devfn);
>   }
>
> +static void pci_adjust_config_limit(PCIBus *bus, uint32_t *limit)
> +{
> +    if (*limit > PCI_CONFIG_SPACE_SIZE) {
> +        if (!pci_bus_is_express(bus)) {
> +            *limit = PCI_CONFIG_SPACE_SIZE;
> +            return;
> +        }
> +
> +        if (!pci_bus_is_root(bus)) {
> +            PCIDevice *bridge = pci_bridge_get_device(bus);
> +            pci_adjust_config_limit(bridge->bus, limit);
> +        }
> +    }
> +}
> +
>   void pci_host_config_write_common(PCIDevice *pci_dev, uint32_t addr,
>                                     uint32_t limit, uint32_t val, uint32_t len)
>   {
> +    pci_adjust_config_limit(pci_dev->bus, &limit);
> +    if (limit <= addr) {
> +        return;
> +    }
> +
>       assert(len <= 4);
>       /* non-zero functions are only exposed when function 0 is present,
>        * allowing direct removal of unexposed functions.
> @@ -70,6 +91,11 @@ uint32_t pci_host_config_read_common(PCIDevice *pci_dev, uint32_t addr,
>   {
>       uint32_t ret;
>
> +    pci_adjust_config_limit(pci_dev->bus, &limit);
> +    if (limit <= addr) {
> +        return ~0x0;
> +    }
> +
>       assert(len <= 4);
>       /* non-zero functions are only exposed when function 0 is present,
>        * allowing direct removal of unexposed functions.
>
>

Quick question: could we check the limit as part of pci_config_size?
Anyway, it looks OK to me.

Reviewed-by: Marcel Apfelbaum <marcel@redhat.com>

Thanks,
Marcel