Re: [PATCH v4 6/9] spapr_pci: add spapr msi read method

["Philippe Mathieu-Daudé" <philmd@redhat.com>]

Cc'ing PCI maintainers

On 8/11/20 1:41 PM, P J P wrote:
> From: Prasad J Pandit <pjp@fedoraproject.org>
> 
> Add spapr msi mmio read method to avoid NULL pointer dereference
> issue.
> 
> Reported-by: Lei Sun <slei.casper@gmail.com>
> Acked-by: David Gibson <david@gibson.dropbear.id.au>
> Reviewed-by: Li Qiang <liq3ea@gmail.com>
> Signed-off-by: Prasad J Pandit <pjp@fedoraproject.org>
> ---
>  hw/ppc/spapr_pci.c | 14 ++++++++++++--
>  1 file changed, 12 insertions(+), 2 deletions(-)
> 
> Update v4: fix multi-line comment and log guest_error
>   -> https://lists.nongnu.org/archive/html/qemu-devel/2020-07/msg05311.html
> 
> diff --git a/hw/ppc/spapr_pci.c b/hw/ppc/spapr_pci.c
> index 363cdb3f7b..53dfd3d8c6 100644
> --- a/hw/ppc/spapr_pci.c
> +++ b/hw/ppc/spapr_pci.c
> @@ -52,6 +52,7 @@
>  #include "sysemu/kvm.h"
>  #include "sysemu/hostmem.h"
>  #include "sysemu/numa.h"
> +#include "qemu/log.h"
>  
>  /* Copied from the kernel arch/powerpc/platforms/pseries/msi.c */
>  #define RTAS_QUERY_FN           0
> @@ -738,6 +739,12 @@ static PCIINTxRoute spapr_route_intx_pin_to_irq(void *opaque, int pin)
>      return route;
>  }
>  
> +static uint64_t spapr_msi_read(void *opaque, hwaddr addr, unsigned size)
> +{
> +    qemu_log_mask(LOG_GUEST_ERROR, "%s: invalid access\n", __func__);
> +    return 0;
> +}
> +
>  /*
>   * MSI/MSIX memory region implementation.
>   * The handler handles both MSI and MSIX.
> @@ -755,8 +762,11 @@ static void spapr_msi_write(void *opaque, hwaddr addr,
>  }
>  
>  static const MemoryRegionOps spapr_msi_ops = {
> -    /* There is no .read as the read result is undefined by PCI spec */
> -    .read = NULL,
> +    /*
> +     * .read result is undefined by PCI spec.
> +     * define .read method to avoid assert failure in memory_region_init_io
> +     */
> +    .read = spapr_msi_read,

Shouldn't this be a read_with_attrs handler returning MEMTX_ERROR
instead? Maybe we need another MemTxResult which does not yet exist.

>      .write = spapr_msi_write,
>      .endianness = DEVICE_LITTLE_ENDIAN
>  };
>