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

[Malcolm Crossley <malcolm.crossley@xxxxxxxxxx>]

On 12/05/14 14:17, Ian Campbell wrote:
> On Mon, 2014-05-12 at 13:42 +0100, Malcolm Crossley 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.
> 
> Since you CC Ian J I assume this is against the qemu-xen-traditional
> tree. Is the same fix needed against upstream qemu?
> 

The fix is only required on qemu-xen-traditional tree.

I have not tested qemu-upstream but it looks fine from code inspection
(line 436 in hw/xen/xen_pt.c has the correct masking on BAR address).

>> ---
>>  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))
>>          r_addr = -1;
>>  
>>      /* align resource size (memory type only) */
> 
> 


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