linux-kernel - Re: [PATCH 3/5] x86: fix pageattr handling for remap percpu allocator

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Date:	Fri, 15 May 2009 08:58:30 +0100
From:	"Jan Beulich" <JBeulich@...ell.com>
To:	"Tejun Heo" <tj@...nel.org>
Cc:	<mingo@...e.hu>, <andi@...stfloor.org>, <tglx@...utronix.de>,
	<linux-kernel@...r.kernel.org>, <hpa@...or.com>
Subject: Re: [PATCH 3/5] x86: fix pageattr handling for remap percpu
	 allocator

>>> Tejun Heo <tj@...nel.org> 15.05.09 06:28 >>>
>@@ -742,6 +744,27 @@ static int cpa_process_alias(struct cpa_data *cpa)
> 	}
> #endif
> 
>+	/*
>+	 * If the PMD page was partially used for per-cpu remapping,
>+	 * the remapped area needs to be split and modified.  Note
>+	 * that the partial recycling only happens at the tail of a
>+	 * partially used PMD page, so touching single PMD page is
>+	 * always enough.
>+	 */
>+	remapped = pcpu_pmd_remapped((void *)vaddr);

vaddr here is the passed-in address, but in order for the lookup to be positive
it needs to be the canonical address (i.e. the one pointing into the 1:1 mapping),
i.e. __va(cpa->pfn << PAGE_SHIFT), just like temp_cpa_vaddr gets calculated
earlier in the same function.

>+	if (remapped) {
>+		int max_pages = PFN_DOWN(PMD_SIZE - (vaddr & ~PMD_MASK));
>+
>+		alias_cpa = *cpa;
>+		temp_cpa_vaddr = (unsigned long)remapped;
>+		alias_cpa.vaddr = &temp_cpa_vaddr;
>+		alias_cpa.numpages = min(alias_cpa.numpages, max_pages);
>+		alias_cpa.flags &= ~(CPA_PAGES_ARRAY | CPA_ARRAY);
>+		ret = __change_page_attr_set_clr(&alias_cpa, 0);
>+		if (ret)
>+			return ret;
>+	}
>+
> 	return 0;
> }

Sorry for not having spotted this yesterday,
Jan

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