* page->tlbflush_timestamp
@ 2013-10-11 14:11 李德新
2013-10-11 14:16 ` page->tlbflush_timestamp Jan Beulich
2013-10-11 14:17 ` page->tlbflush_timestamp Andrew Cooper
0 siblings, 2 replies; 3+ messages in thread
From: 李德新 @ 2013-10-11 14:11 UTC (permalink / raw)
To: xen-devel
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Hi,
page->tlbflush_timestamp is used to filter and flush the TLB whenever
type change of page happens. But why does xen flush TLB upon the type
change? And we already know that guest kernel will flush the TLB in order
to make the page table modifications take effect.
Thanks!
Best regards,
Sam
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^ permalink raw reply [flat|nested] 3+ messages in thread* Re: page->tlbflush_timestamp
2013-10-11 14:11 page->tlbflush_timestamp 李德新
@ 2013-10-11 14:16 ` Jan Beulich
2013-10-11 14:17 ` page->tlbflush_timestamp Andrew Cooper
1 sibling, 0 replies; 3+ messages in thread
From: Jan Beulich @ 2013-10-11 14:16 UTC (permalink / raw)
To: 李德新; +Cc: xen-devel
>>> On 11.10.13 at 16:11, 李德新<topcoder9@gmail.com> wrote:
> page->tlbflush_timestamp is used to filter and flush the TLB whenever
> type change of page happens. But why does xen flush TLB upon the type
> change?
In order to guarantee that the guest won't use stale TLB entries
to subvert the page type tracking.
> And we already know that guest kernel will flush the TLB in order
> to make the page table modifications take effect.
A malicious guest might not.
Jan
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^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: page->tlbflush_timestamp
2013-10-11 14:11 page->tlbflush_timestamp 李德新
2013-10-11 14:16 ` page->tlbflush_timestamp Jan Beulich
@ 2013-10-11 14:17 ` Andrew Cooper
1 sibling, 0 replies; 3+ messages in thread
From: Andrew Cooper @ 2013-10-11 14:17 UTC (permalink / raw)
To: 李德新; +Cc: xen-devel
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On 11/10/13 15:11, 李德新 wrote:
> Hi,
> page->tlbflush_timestamp is used to filter and flush the TLB
> whenever type change of page happens. But why does xen flush TLB upon
> the type change? And we already know that guest kernel will flush the
> TLB in order to make the page table modifications take effect.
>
> Thanks!
>
> Best regards,
> Sam
The comment beside the code you reference explains why this is required
for safety.
On a more pragmatic view however, there is no Xen can trust that guest
kernels are operating correctly.
~Andrew
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