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Re: [Xen-devel] how page faults are handled in paravirtualized xenguests?
- To: "Daniel Stodden" <stodden@xxxxxxxxxx>
- From: weiming <zephyr.zhao@xxxxxxxxx>
- Date: Sat, 22 Mar 2008 22:29:30 -0400
- Cc: xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxx>, tgh <wwwwww4187@xxxxxxxxxxx>
- Delivery-date: Sat, 22 Mar 2008 19:29:56 -0700
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- List-id: Xen developer discussion <xen-devel.lists.xensource.com>
Hi Daniel,
Now, I'm asking for more. :}
1) As you said, in 64-bit mode, PT switch is needed. But on your other post, you said:
"So instead one lets a process, its guest kernel and the VMM share one
virtual address space. As with regular OSes: one address space per guest
process. ïControl transfers between process, kernel and VMM does not
switch between virtual memories, but only privileges, stacks, and EIP.
-> much faster."
The statements above implies that PT switch is not needed. Is it true?
2) in 0/3/3 mode, how guest kernel protects it from application? Simply use different page tables? Will it be too costly (need TLB flush)? Why not use FS, GS to implement 0/1/3 mode?
Many thanks!
Weiming
On Wed, Mar 12, 2008 at 5:37 AM, Daniel Stodden < stodden@xxxxxxxxxx> wrote:
On Tue, 2008-03-11 at 17:28 +0100, Daniel Stodden wrote:
> yes. The ring1 kernel only works if you can play some tricks on virtual
> memory management in order to protect ring1 kernel memory from ring3
> user space (paging alone only distinguishes 0 from 1-3). On x86_32,
ïi should probably correct myself. wrong story, sorry.
of course, paging distingushes ring 0-2 from 3.
so 32-bit in 0/1/3 with segmentation protects xen from the kernel, and
32-bit paging then protects xen and the kernel from user mode.
64-bit paging in 0/3/3 protects xen from both kernel and user mode, but
as i mentioned, you need a PT switch to keep the kernel safe.
maybe more than you asked for :}
daniel
--
Daniel Stodden
LRR - Lehrstuhl fÃr Rechnertechnik und Rechnerorganisation
Institut fÃr Informatik der TU MÃnchen D-85748 Garching
http://www.lrr.in.tum.de/~stodden mailto: stodden@xxxxxxxxxx
PGP Fingerprint: F5A4 1575 4C56 E26A 0B33 3D80 457E 82AE B0D8 735B
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