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xen-devel
[Xen-devel] RE: [RFC] fix xen_in_range()
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To: |
"Keir Fraser" <keir.fraser@xxxxxxxxxxxxx>, "Joseph Cihula" <joseph.cihula@xxxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxx> |
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Subject: |
[Xen-devel] RE: [RFC] fix xen_in_range() |
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From: |
"Jan Beulich" <jbeulich@xxxxxxxxxx> |
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Date: |
Fri, 24 Apr 2009 08:04:40 +0100 |
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Cc: |
Dexuan Cui <dexuan.cui@xxxxxxxxx>, Shane Wang <shane.wang@xxxxxxxxx>, Yunhong Jiang <yunhong.jiang@xxxxxxxxx>, Xiaowei Yang <xiaowei.yang@xxxxxxxxx>, Liping Ke <liping.ke@xxxxxxxxx>, Xin Li <xin.li@xxxxxxxxx> |
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Fri, 24 Apr 2009 00:03:55 -0700 |
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<4F65016F6CB04E49BFFA15D4F7B798D9988CF1A3@xxxxxxxxxxxxxxxxxxxxxxxxxxxx> <C615D676.947F%keir.fraser@xxxxxxxxxxxxx> <4F65016F6CB04E49BFFA15D4F7B798D9988CFA8C@xxxxxxxxxxxxxxxxxxxxxxxxxxxx> |
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>>> "Cihula, Joseph" <joseph.cihula@xxxxxxxxx> 24.04.09 03:26 >>>
>> From: Keir Fraser [mailto:keir.fraser@xxxxxxxxxxxxx]
>> Sent: Thursday, April 23, 2009 12:25 AM
>>
>> On 23/04/2009 00:53, "Cihula, Joseph" <joseph.cihula@xxxxxxxxx> wrote:
>>
>> > Unfortunately, the frametable is only contiguous in the virtual address
>> > space,
>> > so one can't simply take __pa() of its start and end. And since it is
>> > quite
>> > large, iterating through each page to gets its phys addr adds a perceptible
>> > delay when that check has to be done for each page of physical memory (as
>> > is
>> > the case in the only caller, the VT-d routine that maps memory for dom0).
>> > But
>> > it also appears that we can't convert the phys addr arguments into their
>> > virt
>> > addrs to compare with the contiguous frametable range because they will
>> > convert to the DIRECTMAP va's instead.
>>
>> The frametable is allocated in aligned 2MB chunks. So you can check at that
>> granularity rather than 4kB.
>
>That made it just a single iteration on a 2GB system, but what fn should be
>used
>to convert the va to pa? __pa() isn't converting this correctly.
I'm afraid you'll have to either create one, or you'll have to consult the page
tables. Also, how can this be a single iteration on a 2Gb system? struct
page_info is 32 bytes, so I'd expect the frame table to be 16Mb in size (i.e.
eight iterations).
Also, after suggesting to use gb-pages when possible here I realized that
it's probably a latent bug to map more space than was allocated - if the
non-allocated-but-mapped pages happen to later get allocated to a domain,
that domain may change the cacheability attributes of any of these pages,
resulting in aliasing issues. I'll put together a patch for this, but it'll be a
couple of days until I'll be able to do so.
Jan
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