Re: memory operation operand len

If you want to acquire lock for all locked instructions you need to read the
lock (check if the lock is acquired) by all others, right ?
It looks me the same effort as locking a page for ever memory access without
taking care if it is locked instruction or not ...

For the page split instructions -  think you already saw that
read_virtual_yyy would call for read/write_access_linear function where page
split is handled.
The function is already written in the way it checks for both pages before
the read or write actually happens. So at least you can guarantee that no
need to unlock anything in case of a fault.

Could you explain the way you wanna do these locks ?

Stanislav

-----Original Message-----
From: Xin Tong [mailto:[email protected]] 
Sent: Friday, October 19, 2012 10:37 PM
To: Stanislav
Cc: [email protected]
Subject: Re: [Bochs-developers] memory operation operand len

i want to lock the page the atomic memory operation is going to work on .
this way atomic operations can be emulated correctly when the CPUs are
running in parallel.

I happen to add function calls to acquire exclusive ownership of a page just
before the atomic instruction is about to execute.

In case of page fault, i think BOCHS returns to the CPU loop using longjmp.
i  have code to release the exclusive ownership of the page there as well.

Xin


On Fri, Oct 19, 2012 at 3:27 PM, Stanislav <[email protected]> wrote:
> By reading the class bxInstruction_c you cannot know a thing, 
> especially because some instructions access memory multiple times 
> (FXSAVE, REP MOVS) or access variable amount of bytes (VMASKMOV).
>
> I am not talking about many memory access cases which not related to 
> any instruction (page walks, descriptors reads and other system stuff).
>
> Also before the memory access actually happen an instruction might 
> fault so the memory access won't happen.
>
> But what do you want to do ?
>
> Might be I can help ...
>
> If you searching to lock memory before memory access happens you can 
> look for BX_NOTIFY_LIN_MEMORY_ACCESS and BX_NOTIFY_PHY_MEMORY_ACCESS 
> all around the code.
>
> Stanislav
>
> -----Original Message-----
> From: Xin Tong [mailto:[email protected]]
> Sent: Friday, October 19, 2012 9:06 PM
> To: [email protected]
> Subject: [Bochs-developers] memory operation operand len
>
> what is the best way to figure out the length of the memory a memory 
> operation is going to access in BOCHS ? I read the class 
> bxInstruction_c. it does not seem to provide anything to do that ?
>
> Xin
>
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