linux-kernel - Re: [PATCH 04/12] __wr_after_init: x86_64: __wr

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Date:   Thu, 20 Dec 2018 11:27:53 -0800
From:   Matthew Wilcox <willy@...radead.org>
To:     Igor Stoppa <igor.stoppa@...il.com>
Cc:     Andy Lutomirski <luto@...capital.net>,
        Peter Zijlstra <peterz@...radead.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Mimi Zohar <zohar@...ux.vnet.ibm.com>, igor.stoppa@...wei.com,
        Nadav Amit <nadav.amit@...il.com>,
        Kees Cook <keescook@...omium.org>,
        linux-integrity@...r.kernel.org,
        kernel-hardening@...ts.openwall.com, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 04/12] __wr_after_init: x86_64: __wr_op

On Thu, Dec 20, 2018 at 09:19:15PM +0200, Igor Stoppa wrote:
> On 20/12/2018 20:49, Matthew Wilcox wrote:
> > I think you're causing yourself more headaches by implementing this "op"
> > function.
> 
> I probably misinterpreted the initial criticism on my first patchset, about
> duplication. Somehow, I'm still thinking to the endgame of having
> higher-level functions, like list management.
> 
> > Here's some generic code:
> 
> thank you, I have one question, below
> 
> > void *wr_memcpy(void *dst, void *src, unsigned int len)
> > {
> > 	wr_state_t wr_state;
> > 	void *wr_poking_addr = __wr_addr(dst);
> > 
> > 	local_irq_disable();
> > 	wr_enable(&wr_state);
> > 	__wr_memcpy(wr_poking_addr, src, len);
> 
> Is __wraddr() invoked inside wm_memcpy() instead of being invoked privately
> within __wr_memcpy() because the code is generic, or is there some other
> reason?

I was assuming that __wr_addr() might be costly, and we were trying to
minimise the number of instructions executed while write-rare was enabled.