From: David Vrabel <david.vrabel@citrix.com>
To: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
Cc: <linux-kernel@vger.kernel.org>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>, <x86@kernel.org>,
Ingo Molnar <mingo@redhat.com>, "H. Peter Anvin" <hpa@zytor.com>,
<xen-devel@lists.xenproject.org>,
Thomas Gleixner <tglx@linutronix.de>,
Boris Ostrovsky <boris.ostrovsky@oracle.com>
Subject: Re: [Xen-devel] [PATCH 4/4] x86/xen: use the maximum MFN to calculate the required DMA mask
Date: Thu, 20 Nov 2014 11:42:32 +0000 [thread overview]
Message-ID: <546DD3A8.2060404@citrix.com> (raw)
In-Reply-To: <alpine.DEB.2.02.1411191749110.12596@kaball.uk.xensource.com>
On 19/11/14 17:51, Stefano Stabellini wrote:
> On Wed, 19 Nov 2014, David Vrabel wrote:
>>
>> +u64
>> +xen_swiotlb_get_required_mask(struct device *dev)
>> +{
>> + unsigned long max_mfn;
>> +
>> + max_mfn = HYPERVISOR_memory_op(XENMEM_maximum_ram_page, NULL);
>
> As Jan pointed out, I think you need to change the prototype of
> HYPERVISOR_memory_op to return long. Please do consistently across all
> relevant archs.
This doesn't help since 32-bit guests will still truncate. A new
hypercall op that returns the result in a uint64_t parameter is required.
There is another reason why max_mfn isn't suitable -- IOMMU usage so I
think we should assume a 64-bit DMA mask is required (this is actually
the change I put into XenServer's kernel).
David
next prev parent reply other threads:[~2014-11-20 11:42 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-11-19 16:01 [PATCHv3 0/4]: dma, x86, xen: reduce SWIOTLB usage in Xen guests David Vrabel
2014-11-19 16:01 ` [PATCH 1/4] dma: add dma_get_required_mask_from_max_pfn() David Vrabel
2014-11-19 16:01 ` [PATCH 2/4] ia64: use common dma_get_required_mask_from_pfn() David Vrabel
2014-11-19 17:33 ` Stefano Stabellini
2014-11-19 16:02 ` [PATCH 3/4] x86: allow dma_get_required_mask() to be overridden David Vrabel
2014-11-19 16:02 ` [PATCH 4/4] x86/xen: use the maximum MFN to calculate the required DMA mask David Vrabel
2014-11-19 17:51 ` [Xen-devel] " Stefano Stabellini
2014-11-20 11:42 ` David Vrabel [this message]
2014-11-20 11:21 ` Jan Beulich
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