linux-kernel - Re: [PATCH V3 01/13] perf/core, x86: Add PERF_SAMPLE_DATA_PAGE

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Date:   Fri, 8 Feb 2019 11:39:12 +0100 (CET)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     "Liang, Kan" <kan.liang@...ux.intel.com>
cc:     Peter Zijlstra <peterz@...radead.org>, acme@...nel.org,
        mingo@...hat.com, linux-kernel@...r.kernel.org, eranian@...gle.com,
        jolsa@...hat.com, namhyung@...nel.org, ak@...ux.intel.com,
        Andy Lutomirski <luto@...capital.net>
Subject: Re: [PATCH V3 01/13] perf/core, x86: Add
 PERF_SAMPLE_DATA_PAGE_SIZE

On Thu, 31 Jan 2019, Liang, Kan wrote:
> > > +u64 perf_get_page_size(u64 virt)
> > > +{
> > > +	unsigned long flags;
> > > +	unsigned int level;
> > > +	pte_t *pte;
> > > +
> > > +	if (!virt)
> > > +		return 0;
> > > +
> > > +	/*
> > > +	 * Interrupts are disabled, so it prevents any tear down
> > > +	 * of the page tables.
> > > +	 * See the comment near struct mmu_table_batch.
> > > +	 */
> > > +	local_irq_save(flags);
> > > +	if (virt >= TASK_SIZE)
> > > +		pte = lookup_address(virt, &level);
> > > +	else {
> > > +		if (current->mm)
> > > +			pte = lookup_address_in_pgd(pgd_offset(current->mm,
> > > virt),
> > > +						    virt, &level);
> > 
> > Aside from all the missin {}, I'm fairly sure this is broken since this
> > happens from NMI context. This can interrupt switch_mm() and things like
> > use_temporary_mm().
> > 
> > Also; why does this live in the x86 code and not in the generic code?
> > 
> 
> This is x86 implementation.
> In generic code, there is a __weak function. I'll make it clear in the change
> log in v4.

No, instead of hiding it in the changelog, split the patch into two:

 #1 Adding the core stuff including the weak function

 #2 Adding the x86 implementation.

Thanks,

	tglx