Re: [PATCH 03/24] x86/paravirt: Annotate indirect calls

[Juergen Gross]

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