From: David Vrabel <david.vrabel@citrix.com>
To: Jan Beulich <JBeulich@suse.com>
Cc: <x86@kernel.org>, Thomas Gleixner <tglx@linutronix.de>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
<xen-devel@lists.xenproject.org>,
Boris Ostrovsky <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 16:59:10 +0000 [thread overview]
Message-ID: <546391DE.7040508@citrix.com> (raw)
In-Reply-To: <546390FC0200007800046E50@mail.emea.novell.com>
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
>
next prev parent reply other threads:[~2014-11-12 16:59 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 [this message]
2014-11-12 17:18 ` Jan Beulich
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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