lists.openwall.net | lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC | |
Open Source and information security mailing list archives
| ||
|
Date: Fri, 22 May 2009 09:26:47 +0800 From: "Xin, Xiaohui" <xiaohui.xin@...el.com> To: Jeremy Fitzhardinge <jeremy@...p.org>, Chuck Ebbert <cebbert@...hat.com> CC: Ingo Molnar <mingo@...e.hu>, "Li, Xin" <xin.li@...el.com>, "Nakajima, Jun" <jun.nakajima@...el.com>, "H. Peter Anvin" <hpa@...or.com>, Nick Piggin <npiggin@...e.de>, Linux Kernel Mailing List <linux-kernel@...r.kernel.org>, Xen-devel <xen-devel@...ts.xensource.com> Subject: RE: Performance overhead of paravirt_ops on native identified Remember we have done one experiment with "jump", the result shows seems the overhead is even more than the call. Thanks Xiaohui -----Original Message----- From: Jeremy Fitzhardinge [mailto:jeremy@...p.org] Sent: 2009年5月22日 6:49 To: Chuck Ebbert Cc: Ingo Molnar; Xin, Xiaohui; Li, Xin; Nakajima, Jun; H. Peter Anvin; Nick Piggin; Linux Kernel Mailing List; Xen-devel Subject: Re: Performance overhead of paravirt_ops on native identified Chuck Ebbert wrote: > On Wed, 13 May 2009 17:16:55 -0700 > Jeremy Fitzhardinge <jeremy@...p.org> wrote: > > >> Paravirt patching turns all the pvops calls into direct calls, so >> _spin_lock etc do end up having direct calls. For example, the compiler >> generated code for paravirtualized _spin_lock is: >> >> <_spin_lock+0>: mov %gs:0xb4c8,%rax >> <_spin_lock+9>: incl 0xffffffffffffe044(%rax) >> <_spin_lock+15>: callq *0xffffffff805a5b30 >> <_spin_lock+22>: retq >> >> The indirect call will get patched to: >> <_spin_lock+0>: mov %gs:0xb4c8,%rax >> <_spin_lock+9>: incl 0xffffffffffffe044(%rax) >> <_spin_lock+15>: callq <__ticket_spin_lock> >> <_spin_lock+20>: nop; nop /* or whatever 2-byte nop */ >> <_spin_lock+22>: retq >> >> > > Can't those calls be changed to jumps? > In this specific instance of this example, yes. But if you start enabling various spinlock debug options then there'll be code following the call. It would be hard for the runtime patching machinery to know when it would be safe to do the substitution. J
Powered by blists - more mailing lists