Re: [Xen-devel] [PATCH] x86/PCI: fix guest_io_read() when pci_cfg_ok() denies access

[Keir Fraser <keir.xen@xxxxxxxxx>]

On 21/06/2012 13:17, "Jan Beulich" <JBeulich@xxxxxxxx> wrote:

> For a multi-byte aligned read, this so far resulted in 0x00ff to be
> put in the guest's register rather than 0xffff or 0xffffffff, which in
> turn could confuse bus scanning functions (which, when reading vendor
> and/or device IDs, expect to get back all zeroes or all ones).
> 
> As the value gets masked to the read width when merging back into the
> full result, setting the initial value to all ones should not harm any
> or the other cases.
> 
> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>

Acked-by: Keir Fraser <keir@xxxxxxx>

> --- a/xen/arch/x86/traps.c
> +++ b/xen/arch/x86/traps.c
> @@ -1717,7 +1717,7 @@ static uint32_t guest_io_read(
>      while ( bytes != 0 )
>      {
>          unsigned int size = 1;
> -        uint32_t sub_data = 0xff;
> +        uint32_t sub_data = ~0;
>  
>          if ( (port == 0x42) || (port == 0x43) || (port == 0x61) )
>          {
> 
> 
> 
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