Re: [PATCH v4 08/14] vfio-user: handle PCI config space accesses

[Stefan Hajnoczi]

On Wed, Dec 15, 2021 at 10:35:32AM -0500, Jagannathan Raman wrote:
> Define and register handlers for PCI config space accesses
> 
> Signed-off-by: Elena Ufimtseva <elena.ufimtseva@oracle.com>
> Signed-off-by: John G Johnson <john.g.johnson@oracle.com>
> Signed-off-by: Jagannathan Raman <jag.raman@oracle.com>
> ---
>  hw/remote/vfio-user-obj.c | 45 +++++++++++++++++++++++++++++++++++++++
>  hw/remote/trace-events    |  2 ++
>  2 files changed, 47 insertions(+)
> 
> diff --git a/hw/remote/vfio-user-obj.c b/hw/remote/vfio-user-obj.c
> index a01a0ad185..c6d0c675b7 100644
> --- a/hw/remote/vfio-user-obj.c
> +++ b/hw/remote/vfio-user-obj.c
> @@ -43,6 +43,7 @@
>  #include "qapi/qapi-visit-sockets.h"
>  #include "qemu/notify.h"
>  #include "qemu/thread.h"
> +#include "qemu/main-loop.h"
>  #include "sysemu/sysemu.h"
>  #include "libvfio-user.h"
>  #include "hw/qdev-core.h"
> @@ -174,6 +175,39 @@ retry_attach:
>      qemu_set_fd_handler(o->vfu_poll_fd, vfu_object_ctx_run, NULL, o);
>  }
>  
> +static ssize_t vfu_object_cfg_access(vfu_ctx_t *vfu_ctx, char * const buf,
> +                                     size_t count, loff_t offset,
> +                                     const bool is_write)
> +{
> +    VfuObject *o = vfu_get_private(vfu_ctx);
> +    uint32_t pci_access_width = sizeof(uint32_t);
> +    size_t bytes = count;
> +    uint32_t val = 0;
> +    char *ptr = buf;
> +    int len;
> +
> +    while (bytes > 0) {
> +        len = (bytes > pci_access_width) ? pci_access_width : bytes;
> +        if (is_write) {
> +            memcpy(&val, ptr, len);
> +            pci_host_config_write_common(o->pci_dev, offset,
> +                                         pci_config_size(o->pci_dev),
> +                                         val, len);
> +            trace_vfu_cfg_write(offset, val);
> +        } else {
> +            val = pci_host_config_read_common(o->pci_dev, offset,
> +                                              pci_config_size(o->pci_dev), 
> len);
> +            memcpy(ptr, &val, len);
> +            trace_vfu_cfg_read(offset, val);
> +        }
> +        offset += len;
> +        ptr += len;
> +        bytes -= len;
> +    }
> +
> +    return count;
> +}
> +
>  /*
>   * TYPE_VFU_OBJECT depends on the availability of the 'socket' and 'device'
>   * properties. It also depends on devices instantiated in QEMU. These
> @@ -244,6 +278,17 @@ static void vfu_object_init_ctx(VfuObject *o, Error 
> **errp)
>          goto fail;
>      }
>  
> +    ret = vfu_setup_region(o->vfu_ctx, VFU_PCI_DEV_CFG_REGION_IDX,
> +                           pci_config_size(o->pci_dev), 
> &vfu_object_cfg_access,
> +                           VFU_REGION_FLAG_RW | VFU_REGION_FLAG_ALWAYS_CB,
> +                           NULL, 0, -1, 0);

Thanos or John: QEMU's pci_host_config_read/write_common() works with
host-endian values. I don't know which endianness libvfio-user's region
callbacks expect. Does this patch look endian-safe to you (e.g. will it
work on a big-endian host)?

Thanks,
Stefan

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