linux-kernel - Re: [PATCH] vfio powerpc: enabled on powernv platform

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Message-ID: <50B84F4E.20809@ozlabs.ru>
Date:	Fri, 30 Nov 2012 17:16:46 +1100
From:	Alexey Kardashevskiy <aik@...abs.ru>
To:	Alex Williamson <alex.williamson@...hat.com>
CC:	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Paul Mackerras <paulus@...ba.org>,
	linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org,
	David Gibson <david@...son.dropbear.id.au>
Subject: Re: [PATCH] vfio powerpc: enabled on powernv platform

On 29/11/12 15:20, Alex Williamson wrote:

>> +	/* Put tces to the table */
>> +	for (i = 0; (i < pages) && !ret; ++i, tce += IOMMU_PAGE_SIZE) {
>> +		ret = put_tce(tbl, entry + i, tce, direction);
>> +		/*
>> +		 * As IOMMU page size is always 4K, the system page size
>> +		 * can be 64K and there is no special tracking for IOMMU pages,
>> +		 * we only do rlimit check/update for the very first
>> +		 * 4K IOMMUpage within 64K system page.
>> +		 */
>> +		if (!(tce & ~PAGE_MASK))
>> +			++retpages;
>
> Ah, here's the comment I was looking for, though I'm still not sure
> about the read/write bits.
>
> Isn't there an exploit here that a user can lock pages beyond their
> limits if they just skip mapping the first 4k of each page?  Thanks,


Heh. True. Posted another patch with 4K pages per system page usage tracking.



-- 
Alexey
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