Re: [Xen-devel] [PATCH] hw/passthrough: Prevent QEMU from mapping PCI option ROM at address 0

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 12.05.14 at 14:42, <malcolm.crossley@xxxxxxxxxx> wrote:
> The PCI option ROM BAR uses the LSB to indicate if the BAR is enabled.
> The AMD graphics driver sets the address bit's of the BAR to 0 but leaves the
> LSB set to 1. Whilst this is not good practice, QEMU should be ignoring the
> non address parts of the BAR.
> 
> This patch adds masking of the non address parts of the BAR before comparing
> the address to 0.
> ---
>  hw/pass-through.c |    2 +-
>  1 files changed, 1 insertions(+), 1 deletions(-)
> 
> diff --git a/hw/pass-through.c b/hw/pass-through.c
> index 304c438..7d6aefc 100644
> --- a/hw/pass-through.c
> +++ b/hw/pass-through.c
> @@ -2208,7 +2208,7 @@ static void pt_bar_mapping_one(struct pt_dev *ptdev, 
> int bar, int io_enable,
>      }
>  
>      /* prevent guest software mapping memory resource to 00000000h */
> -    if ((base->bar_flag == PT_BAR_FLAG_MEM) && (r_addr == 0))
> +    if ((base->bar_flag == PT_BAR_FLAG_MEM) && ((r_addr & 
> PCI_BASE_ADDRESS_MEM_MASK) == 0))

You talk of the low bit, but mask off the low 4 - how does that fit
together? Didn't you rather mean PCI_ROM_ADDRESS_MASK &
~PCI_ROM_ADDRESS_ENABLE in text and code?

Jan


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