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From: Juergen Gross <jgross@suse.com>
To: Peter Zijlstra <peterz@infradead.org>,
	David Woodhouse <dwmw2@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>,
	Josh Poimboeuf <jpoimboe@redhat.com>,
	linux-kernel@vger.kernel.org, Dave Hansen <dave.hansen@intel.com>,
	Ashok Raj <ashok.raj@intel.com>,
	Tim Chen <tim.c.chen@linux.intel.com>,
	Andy Lutomirski <luto@kernel.org>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	Greg KH <gregkh@linuxfoundation.org>,
	Andrea Arcangeli <aarcange@redhat.com>,
	Andi Kleen <ak@linux.intel.com>,
	Arjan Van De Ven <arjan.van.de.ven@intel.com>,
	Dan Williams <dan.j.williams@intel.com>,
	Paolo Bonzini <pbonzini@redhat.com>,
	Jun Nakajima <jun.nakajima@intel.com>,
	Asit Mallick <asit.k.mallick@intel.com>,
	Jason Baron <jbaron@akamai.com>
Subject: Re: [PATCH 03/24] x86/paravirt: Annotate indirect calls
Date: Thu, 25 Jan 2018 11:26:57 +0100	[thread overview]
Message-ID: <81ade568-6ab3-a62a-5026-5138f2313ab3@suse.com> (raw)
In-Reply-To: <20180125102253.GB2228@hirez.programming.kicks-ass.net>

On 25/01/18 11:22, Peter Zijlstra wrote:
> On Thu, Jan 25, 2018 at 10:02:05AM +0000, David Woodhouse wrote:
>> On Tue, 2018-01-23 at 16:25 +0100, Peter Zijlstra wrote:
>>> Paravirt emits indirect calls which get flagged by objtool retpoline
>>> checks, annotate it away because all these indirect calls will be
>>> patched out before we start userspace.
>>
>> I've seen this asserted repeatedly but I've never truly convinced
>> myself of it. Is this absolutely unconditionally true in every case,
>> even when we're running as a guest and there are *actual* calls to be
>> made? We turn them into direct calls, never leave them indirect?
> 
> That is my understanding; and when I worked on the paravirt spinlock
> code and disassembled live guest code this seemed to have happend.
> 
> But let me go read the paravirt code again to make a stronger argument
> in favour.
> 

paravirt_patch_default() is the function you want to look at: it either
replaces the indirect call by some cutom code (which is never an
indirect call) or by a call of the target function.


Juergen

  reply	other threads:[~2018-01-25 10:26 UTC|newest]

Thread overview: 71+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-01-23 15:25 [PATCH 00/24] objtool: retpoline and asm-goto validation Peter Zijlstra
2018-01-23 15:25 ` [PATCH 01/24] objtool: Use existing global variables for options Peter Zijlstra
2018-01-23 15:25 ` [PATCH 02/24] objtool: Add retpoline validation Peter Zijlstra
2018-01-23 18:21   ` Borislav Petkov
2018-01-26  9:54   ` David Woodhouse
2018-01-23 15:25 ` [PATCH 03/24] x86/paravirt: Annotate indirect calls Peter Zijlstra
2018-01-25 10:02   ` David Woodhouse
2018-01-25 10:22     ` Peter Zijlstra
2018-01-25 10:26       ` Juergen Gross [this message]
2018-01-25 10:52         ` David Woodhouse
2018-01-25 11:35           ` Peter Zijlstra
2018-01-26  9:57             ` David Woodhouse
2018-01-29 17:58   ` Josh Poimboeuf
2018-01-29 18:09     ` David Woodhouse
2018-01-29 18:17     ` Peter Zijlstra
2018-01-29 18:38   ` Josh Poimboeuf
2018-01-29 19:21     ` Peter Zijlstra
2018-01-30 16:02       ` Josh Poimboeuf
2018-01-31  4:13         ` [PATCH] x86/paravirt: Remove 'noreplace-paravirt' cmdline option Josh Poimboeuf
2018-01-31  5:59           ` Juergen Gross
2018-01-31  9:42           ` [tip:x86/pti] " tip-bot for Josh Poimboeuf
2018-01-23 15:25 ` [PATCH 04/24] x86,nospec: Annotate indirect calls/jumps Peter Zijlstra
2018-01-26 10:19   ` David Woodhouse
2018-01-29 17:44     ` Peter Zijlstra
2018-01-23 15:25 ` [PATCH 05/24] x86: Annotate indirect jump in head_64.S Peter Zijlstra
2018-01-26 10:24   ` David Woodhouse
2018-01-23 15:25 ` [PATCH 06/24] x86,kvm: Fix indirect calls in emulator Peter Zijlstra
2018-01-23 20:28   ` Borislav Petkov
2018-01-23 20:48     ` David Woodhouse
2018-01-24 10:35       ` Peter Zijlstra
2018-01-24 10:43         ` Paolo Bonzini
2018-01-25  9:34           ` Peter Zijlstra
2018-01-25  9:49             ` David Woodhouse
2018-01-26 10:57             ` Paolo Bonzini
2018-01-23 15:25 ` [PATCH 07/24] x86,vmx: Fix indirect call Peter Zijlstra
2018-01-25  9:36   ` Peter Zijlstra
2018-01-23 15:25 ` [PATCH 08/24] x86,sme: Annotate " Peter Zijlstra
2018-01-26 10:37   ` David Woodhouse
2018-01-29 17:49     ` Peter Zijlstra
2018-01-29 17:50       ` Peter Zijlstra
2018-01-31  9:29     ` Peter Zijlstra
2018-01-31 15:04       ` Josh Poimboeuf
2018-01-31 16:00         ` Peter Zijlstra
2018-01-23 15:25 ` [PATCH 09/24] jump_label: Add branch hints to static_branch_{un,}likely() Peter Zijlstra
2018-01-24 18:46   ` Borislav Petkov
2018-01-23 15:25 ` [PATCH 10/24] sched: Optimize ttwu_stat() Peter Zijlstra
2018-01-23 15:25 ` [PATCH 11/24] x86: Reindent _static_cpu_has Peter Zijlstra
2018-01-23 15:25 ` [PATCH 12/24] x86: Update _static_cpu_has to use all named variables Peter Zijlstra
2018-01-25 19:31   ` Borislav Petkov
2018-01-23 15:25 ` [PATCH 13/24] objtool: Implement base jump_assert support Peter Zijlstra
2018-01-26 10:45   ` David Woodhouse
2018-01-23 15:25 ` [PATCH 14/24] x86: Add a type field to alt_instr Peter Zijlstra
2018-01-23 15:25 ` [PATCH 15/24] x86: Annotate static_cpu_has alternative Peter Zijlstra
2018-01-23 15:25 ` [PATCH 16/24] objtool: Implement jump_assert for _static_cpu_has() Peter Zijlstra
2018-01-23 15:25 ` [PATCH 17/24] objtool: Introduce special_type Peter Zijlstra
2018-01-23 15:25 ` [PATCH 18/24] objtool: More complex static jump implementation Peter Zijlstra
2018-01-23 15:25 ` [PATCH 19/24] objtool: Even more complex static block checks Peter Zijlstra
2018-01-23 15:25 ` [PATCH 20/24] objtool: Another static block fail Peter Zijlstra
2018-01-29 22:52   ` Josh Poimboeuf
2018-01-30  9:56     ` Peter Zijlstra
2018-01-31  3:12       ` Josh Poimboeuf
2018-01-31 10:01         ` Peter Zijlstra
2018-01-31 10:07           ` David Woodhouse
2018-01-31 10:27             ` Peter Zijlstra
2018-01-23 15:26 ` [PATCH 21/24] objtool: Skip static assert when KCOV/KASAN Peter Zijlstra
2018-01-23 15:26 ` [PATCH 22/24] x86/jump_label: Implement arch_static_assert() Peter Zijlstra
2018-01-23 15:26 ` [PATCH 23/24] x86: Force asm-goto Peter Zijlstra
2018-01-23 15:26 ` [PATCH 24/24] x86: Remove FAST_FEATURE_TESTS Peter Zijlstra
2018-01-23 15:42 ` [PATCH 00/24] objtool: retpoline and asm-goto validation Peter Zijlstra
2018-01-23 15:57   ` David Woodhouse
2018-01-23 16:03     ` Peter Zijlstra

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