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SubjectRe: [Xen-devel] [PATCH 3/3] x86/xen: use the maximum MFN to calculate the required DMA mask
>>> On 12.11.14 at 17:59, <david.vrabel@citrix.com> wrote:
> On 12/11/14 15:55, Jan Beulich wrote:
>>>>> On 12.11.14 at 16:25, <david.vrabel@citrix.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.
>
> The docs in include/public/memory.h say:
>
> "Returns the maximum machine frame number of mapped RAM in this system."
>
> Which sounds inclusive to me... Do we need a doc update here?

Possibly - the origin of this is Linux'es mis-named "max_page" I believe.
And in any event I'd expect you to base your code changes on reality,
not just on documentation...

Jan



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