Re: [PATCH 3/5] pci-assign: Fix dword read at PCI_COMMAND

[Alex Williamson <alex.williamson@redhat.com>]

On Thu, 2011-04-28 at 10:59 +0200, Jan Kiszka wrote:
> If we emulate the command register, we must only read its content from
> the shadow config space. For dword read of both PCI_COMMAND and
> PCI_STATUS, at least the latter must be read from the device.
> 
> For simplicity reasons and as the code path is not considered
> performance critical for the affected SRIOV devices, the fix performes
> device access to the command word unconditionally, even if emulation is
> enabled and only that word is read.
> 
> Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
> ---
>  hw/device-assignment.c |    8 +++++---
>  1 files changed, 5 insertions(+), 3 deletions(-)
> 
> diff --git a/hw/device-assignment.c b/hw/device-assignment.c
> index f37f108..ee81434 100644
> --- a/hw/device-assignment.c
> +++ b/hw/device-assignment.c
> @@ -482,14 +482,11 @@ static uint32_t assigned_dev_pci_read_config(PCIDevice *d, uint32_t address,
>      /*
>       * Catch access to
>       *  - vendor & device ID
> -     *  - command register (if emulation needed)
>       *  - base address registers
>       *  - ROM base address & capability pointer
>       *  - interrupt line & pin
>       */
>      if (ranges_overlap(address, len, PCI_VENDOR_ID, 4) ||
> -        (pci_dev->need_emulate_cmd &&
> -         ranges_overlap(address, len, PCI_COMMAND, 2)) ||
>          ranges_overlap(address, len, PCI_BASE_ADDRESS_0, 24) ||
>          ranges_overlap(address, len, PCI_ROM_ADDRESS, 8) ||
>          ranges_overlap(address, len, PCI_INTERRUPT_LINE, 2)) {
> @@ -521,6 +518,11 @@ do_log:
>      DEBUG("(%x.%x): address=%04x val=0x%08x len=%d\n",
>            (d->devfn >> 3) & 0x1F, (d->devfn & 0x7), address, val, len);
>  
> +    if (pci_dev->need_emulate_cmd) {
> +        val = merge_bits(val, pci_default_read_config(d, PCI_COMMAND, 2),
> +                         address, len, PCI_COMMAND, 0xffff);

Shouldn't this be pci_default_read_config(d, address, len)?  I think
what you have works since PCI_COMMAND is at the start of a dword, but it
violates the merge_bits() assumption that val and mval are from the same
address with the same length.  Thanks,

Alex

> +    }
> +
>      if (!pci_dev->cap.available) {
>          /* kill the special capabilities */
>          if (address == PCI_COMMAND && len == 4) {