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

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Message-Id: <546390FC0200007800046E50@mail.emea.novell.com>
Date:	Wed, 12 Nov 2014 15:55:24 +0000
From:	"Jan Beulich" <JBeulich@...e.com>
To:	"David Vrabel" <david.vrabel@...rix.com>
Cc:	<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. Peter Anvin" <hpa@...or.com>
Subject: Re: [Xen-devel] [PATCH 3/3] x86/xen: use the maximum MFN to
 calculate the required DMA mask

>>> 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.
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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