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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 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?

> Hence I'd suggest
>
> u64
> xen_swiotlb_get_required_mask(struct device *dev)
> {
> unsigned long max_mfn;
>
> max_mfn = HYPERVISOR_memory_op(XENMEM_maximum_ram_page, NULL);
>
> return DMA_BIT_MASK(__fls(max_mfn - 1) + 1 + PAGE_SHIFT);
> }
>
> Jan
>



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