From: "Jan Beulich" <JBeulich@suse.com>
To: "David Vrabel" <david.vrabel@citrix.com>
Cc: <x86@kernel.org>, "Thomas Gleixner" <tglx@linutronix.de>,
"Greg Kroah-Hartman" <gregkh@linuxfoundation.org>,
<xen-devel@lists.xenproject.org>,
"BorisOstrovsky" <boris.ostrovsky@oracle.com>,
"Ingo Molnar" <mingo@redhat.com>, <linux-kernel@vger.kernel.org>,
"H. Peter Anvin" <hpa@zytor.com>
Subject: Re: [Xen-devel] [PATCH 3/3] x86/xen: use the maximum MFN to calculate the required DMA mask
Date: Wed, 12 Nov 2014 17:18:34 +0000 [thread overview]
Message-ID: <5463A47A0200007800046F19@mail.emea.novell.com> (raw)
In-Reply-To: <546391DE.7040508@citrix.com>
>>> 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
next prev parent reply other threads:[~2014-11-12 17:18 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-11-12 15:25 [PATCHv2 0/3]: dma,x86,xen: reduce SWIOTLB usage in Xen guests David Vrabel
2014-11-12 15:25 ` [PATCH 1/3] dma,ia64: add dma_get_required_mask_from_max_pfn() David Vrabel
2014-11-14 15:11 ` [Xen-devel] [PATCH 1/3] dma, ia64: " Stefano Stabellini
2014-11-12 15:25 ` [PATCH 2/3] x86: allow dma_get_required_mask() to be overridden David Vrabel
2014-11-13 10:25 ` [Xen-devel] " Jan Beulich
2014-11-13 10:30 ` David Vrabel
2014-11-13 10:32 ` Jan Beulich
2014-11-14 15:19 ` Stefano Stabellini
2014-11-12 15:25 ` [PATCH 3/3] x86/xen: use the maximum MFN to calculate the required DMA mask David Vrabel
2014-11-12 15:55 ` [Xen-devel] " Jan Beulich
2014-11-12 16:59 ` David Vrabel
2014-11-12 17:18 ` Jan Beulich [this message]
2014-11-13 9:57 ` Jan Beulich
2014-11-13 10:38 ` Andrew Cooper
2014-11-13 10:53 ` Jan Beulich
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