linux-kernel - Re: [Xen-devel] [PATCH 3/3] x86/xen: use the maximum MFN to calculate the required DMA mask

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Date:	Thu, 13 Nov 2014 10:53:22 +0000
From:	"Jan Beulich" <JBeulich@...e.com>
To:	"Andrew Cooper" <andrew.cooper3@...rix.com>
Cc:	"David Vrabel" <david.vrabel@...rix.com>, <x86@...nel.org>,
	"Thomas Gleixner" <tglx@...utronix.de>,
	"Greg Kroah-Hartman" <gregkh@...uxfoundation.org>,
	<xen-devel@...ts.xenproject.org>,
	"Boris Ostrovsky" <boris.ostrovsky@...cle.com>,
	"Ingo Molnar" <mingo@...hat.com>, <linux-kernel@...r.kernel.org>,
	"H. PeterAnvin" <hpa@...or.com>
Subject: Re: [Xen-devel] [PATCH 3/3] x86/xen: use the maximum MFN to
 calculate the required DMA mask

>>> On 13.11.14 at 11:38, <andrew.cooper3@...rix.com> wrote:
> On 12/11/14 15:55, Jan Beulich wrote:
>>>>> On 12.11.14 at 16:25, <david.vrabel@...rix.com> wrote:
>>> +u64
>>> +xen_swiotlb_get_required_mask(struct device *dev)
>>> +{
>>> +	u64 max_mfn;
>>> +
>>> +	max_mfn = HYPERVISOR_memory_op(XENMEM_maximum_ram_page, NULL);
>>> +
>>> +	return DMA_BIT_MASK(fls64(max_mfn << PAGE_SHIFT) + 1);
>>> +}
>> The value the hypercall returns is exclusive and an unsigned long.
> 
> All hypercalls return long, despite lack of clarity, or in some cases,
> documentation to the contrary.

The emphasis wasn't on "unsigned" but on "long". But see also my
later reply to that same mail.

Jan

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