Messages in this thread | | | Date | Wed, 12 Nov 2014 17:18:34 +0000 | From | "Jan Beulich" <> | Subject | Re: [Xen-devel] [PATCH 3/3] x86/xen: use the maximum MFN to calculate the required DMA mask |
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>>> 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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