linux-kernel - Re: [PATCH v2 1/2] xen-pciback: return proper values during BAR sizing

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Date:	Tue, 07 Jun 2016 08:14:04 -0600
From:	"Jan Beulich" <JBeulich@...e.com>
To:	"David Vrabel" <david.vrabel@...rix.com>,
	"Boris Ostrovsky" <boris.ostrovsky@...cle.com>,
	"Konrad Rzeszutek Wilk" <konrad.wilk@...cle.com>,
	"Juergen Gross" <JGross@...e.com>
Cc:	"xen-devel" <xen-devel@...ts.xenproject.org>,
	<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 1/2] xen-pciback: return proper values during
 BAR sizing

>>> On 07.06.16 at 16:06, <boris.ostrovsky@...cle.com> wrote:
> On 06/07/2016 02:30 AM, Jan Beulich wrote:
>> Reads following writes with all address bits set to 1 should return all
>> changeable address bits as one, not the BAR size (nor, as was the case
>> for the upper half of 64-bit BARs, the high half of the region's end
>> address). Presumably this didn't cause any problems so far because
>> consumers use the value to calculate the size (usually via val & -val),
>> and do nothing else with it.
>>
>> But also consider the exception here: Unimplemented BARs should always
>> return all zeroes.
>>
>> And finally, the check for whether to return the sizing address on read
>> for the ROM BAR should ignore all non-address bits, not just the ROM
>> Enable one.
> 
> 
> Should this go to stable trees as well?

Not sure - we had no active reports of problems. The context this
was found in did not really have an issue because it was broken.
I guess I'll leave this to you maintainers...

Jan