Slides from the Xen Winter Summit at Austin are starting to show up. Our Xen/IOMMU Integration should be there soon.
January 18, 2006
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Slides from the Xen Winter Summit at Austin are starting to show up. Our Xen/IOMMU Integration should be there soon.
RSS feed for comments on this post. TrackBack URI
interesting slides !
I saw in your slides the term DAC.
What is DAC ?
DMAC stands for Direct Memory Access Controller (DMAC).
Does DAC has to to with DMA/DMAC?
Comment by Anonymous — January 19, 2006 @ 7:16 AM |
Re: interesting slides !
Not Muli, but still an answer: AFAIK DAC stands for Double Address Cycle, meaninig sending an address in a transaction (like DMA) in two bus transfers, not one. Usefull when the possible size of the address is bigger then the bus width.
Gilad
Comment by Anonymous — January 19, 2006 @ 9:34 AM |
Re: interesting slides !
DAC is double address cycle – a PCI mechanism by which a device with 32 address lines pushes out a 64 bit address in two cycles, low half first and then high half.
Comment by mulix — January 19, 2006 @ 12:19 PM |
are you coming to the OS lecutre in the technion or not?
?
Comment by Anonymous — January 25, 2006 @ 7:11 PM |
Re: are you coming to the OS lecutre in the technion or not?
Not this semester, no. Too many other obligations in the next month and a half.
Comment by mulix — January 25, 2006 @ 8:55 PM |
2 questions about DMA and Xen
– thanks for that link.
– I am a DMA ignorant.
2 questions (if I may: little late, but better than never):
1) is the DMA problem ** in XEN ** restricted to 64 bit processors ?
will 32 bit processors work in Xen with no fear that one domain will DMA into memory of a second domain ?
2) “The Xen unstable tree does not support any HW
IOMMUs.”
I am also IOMMU ignorant.
Does the linux kernel for x86 ,IA-64 and x86_64 includes
support for HW IOMMU ? in case it does – is it builtin and
activated by default , or you should somehow activate (or patch the kernel
,etc)
you say in the slides:
“swiotlb and grant tables can be considered SW
implementations of IOMMU functionality.”
If I am not wrong,in IA64 (I am speaking about ordinary linux ,not Xen) swiotlb is used as an implementation
of IOMMU.
But: Can grant tables of Xen , with their shared pages mechanism, solve the problem of two domains
which access **through DMA** the same address ?
is such solution better than swiotlb in any aspect ? (which has it’s cost)
DMA&IOMMU ignorant
Comment by Anonymous — January 27, 2006 @ 7:54 PM |
Re: 2 questions about DMA and Xen
> 1) is the DMA problem ** in XEN ** restricted to 64 bit processors ?
>
> will 32 bit processors work in Xen with no fear that one domain will DMA
> into memory of a second domain ?
No, this is an architectural issue unrelated to the native word size. Note that both 32 and 64 bits processors suffer from this problem if granting *untrusted* domains direct HW access. Since Xen at the moment only grants trusted domains direct HW access, this is not a problem.
> Does the linux kernel for x86 ,IA-64 and x86_64 includes
> support for HW IOMMU ?
x86 – no, IA-64 – no, x86-64 – yes. Again, this is architectural – there are no x86 and IA-64 machines with HW IOMMUs. There are x86-64 machines (AMD Opterons, for example) with a HW IOMMU.
> in case it does – is it builtin and
> activated by default , or you should somehow activate (or patch the kernel
> ,etc)
On x86-64 Opteron machines it is activated by default if necessary (e.g., you have more than 4GB of memory).
> “swiotlb and grant tables can be considered SW implementations of IOMMU
> functionality.”
> If I am not wrong,in IA64 (I am speaking about ordinary linux ,not Xen)
> wiotlb is used as an implementation of IOMMU.
Right.
> But: Can grant tables of Xen , with their shared pages mechanism, solve the
> problem of two domains which access **through DMA** the same address ?
> is such solution better than swiotlb in any aspect ? (which has it’s cost)
grant tables attempt to address the isolation requirement, that is, letting one domain trigger a DMA into another domain’s memory, while doing it “securely”. swiotlb addresses different things (4GB DMA limited devices in Linux, same + non-machine-contigous DMAs in Xen).
Comment by mulix — January 28, 2006 @ 5:31 PM |