linux-kernel - Re: [PATCH 2/2] ptrace_vm: ptrace for syscall emulation virtual machines

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Date:	Mon, 16 Mar 2009 13:17:32 +0100
From:	Renzo Davoli <renzo@...unibo.it>
To:	Am??rico Wang <xiyou.wangcong@...il.com>
Cc:	Ingo Molnar <mingo@...e.hu>, linux-kernel@...r.kernel.org,
	Jeff Dike <jdike@...toit.com>,
	user-mode-linux-devel@...ts.sourceforge.net
Subject: Re: [PATCH 2/2] ptrace_vm: ptrace for syscall emulation virtual
	machines

Dear Cong,

Thank you for the detailed analysis of the code.
I'll change the code taking care of your observations asap.

On Mon, Mar 16, 2009 at 04:15:08PM +0800, Am??rico Wang wrote:
> >I have updated the patch, now it should be (more) consistent
> >with the Coding Style specifications.
> You can use scripts/checkpatch.pl to check it before sending.
I read the coding style document and I used the perl script.
However, the script is not able to cope with all the style specifications
and I may have missed something more. 
> 
> >UML tests at startup which features are provided and uses PTRACE_VM or
> >PTRACE_SYSEMU (or nothing). PTRACE_VM and/or PTRACE_SYSEMU support can be
> >disabled by command line flags.
> So what? PTRACE_VM is only supported in UML with this patch,
> UML still has to use PTRACE_SYSEMU on x86_32.
> 
> Am I missing something? :)
This patch [2/2] is for UML (host and guest). Patch #1 provides PTRACE_VM
for all the architectures supporting ptrace via tracehook.
By applying both patches PTRACE_VM is available in the following architectures:
x86*, sparc*, s390, powerpc*, ia64, sh* and um.
(I have not tested all these architectures, but the patch applies to the core ptrace
code, shared by all of them).
Ptrace_vm then provides the same speedup of PTRACE_SYSEMU extending its support:
- to other architectures: ports of UML or similar code for other architectures can
use it
- to other applications: PTRACE_SYSEMU supports the virtualization of all the system calls
while by PTRACE_VM the VM monitor can virtualize some of the system calls, depending on
some condition e.g. the value of a parameter. It is possible in this way give a faster
implementation to partial virtual machines like my umview.  

With patch #2 user-mode linux also uses ptrace_vm where available.

renzo
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