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

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Date:	Wed, 18 Mar 2009 22:39:39 +0800
From:	Américo Wang <xiyou.wangcong@...il.com>
To:	Renzo Davoli <renzo@...unibo.it>
Cc:	Am??rico Wang <xiyou.wangcong@...il.com>,
	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

On Mon, Mar 16, 2009 at 01:17:32PM +0100, Renzo Davoli wrote:
>Dear Cong,
>
>Thank you for the detailed analysis of the code.
>I'll change the code taking care of your observations asap.


You are so welcome. :)

>
>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).

Ok then. I am not familiar with tracehooks.

>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.
>

Thanks for your explanations!

-- 
Do what you love, f**k the rest! F**k the regulations!
 
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