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From: Kit Chow <kchow@gigaio.com>
To: Logan Gunthorpe <logang@deltatee.com>,
	Robin Murphy <robin.murphy@arm.com>,
	Dave Jiang <dave.jiang@intel.com>,
	Eric Pilmore <epilmore@gigaio.com>,
	Bjorn Helgaas <helgaas@kernel.org>
Cc: "linux-pci@vger.kernel.org" <linux-pci@vger.kernel.org>,
	Alex Williamson <alex.williamson@redhat.com>,
	David Woodhouse <dwmw2@infradead.org>,
	"iommu@lists.linux-foundation.org"
	<iommu@lists.linux-foundation.org>
Subject: Re: IOAT DMA w/IOMMU
Date: Mon, 13 Aug 2018 16:48:34 -0700	[thread overview]
Message-ID: <bcfc8738-cbf6-7124-3d79-a1bdfe161d36@gigaio.com> (raw)
In-Reply-To: <0e839acf-5948-42aa-2ad6-72ca0d84a8c3@deltatee.com>



On 08/13/2018 04:39 PM, Logan Gunthorpe wrote:
>
> On 13/08/18 05:30 PM, Kit Chow wrote:
>> In arch/x86/include/asm/page.h, there is the following comment in
>> regards to validating the virtual address.
>>
>> /*
>>   * virt_to_page(kaddr) returns a valid pointer if and only if
>>   * virt_addr_valid(kaddr) returns true.
>>   */
>> #define virt_to_page(kaddr)     pfn_to_page(__pa(kaddr) >> PAGE_SHIFT)
>>
>> So it looks like the validation by virt_addr_valid was somehow dropped
>> from the virt_to_page code path. Does anyone have any ideas what
>> happended to it?
> I don't think it was ever validated (though I haven't been around long
> enough to say for certain). What the comment is saying is that you
> shouldn't rely on virt_to_page() unless you know virt_addr_valid() is
> true (which in most cases you can without the extra check). virt_to_page
> is meant to be really fast so adding an extra validation would probably
> be a significant performance regression for the entire kernel.
>
> The fact that this can happen through dma_map_single() is non-ideal at
> best. It assumes the caller is mapping regular memory and doesn't check
> this at all. It may make sense to fix that but I think people expect
> dma_map_single() to be as fast as possible as well...
>
Perhaps include the validation with some debug turned on?

  reply	other threads:[~2018-08-13 23:48 UTC|newest]

Thread overview: 48+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-08-09 18:14 IOAT DMA w/IOMMU Eric Pilmore
2018-08-09 18:43 ` Bjorn Helgaas
2018-08-09 18:51   ` Eric Pilmore
2018-08-09 19:35     ` Logan Gunthorpe
2018-08-09 19:47       ` Kit Chow
2018-08-09 20:11         ` Logan Gunthorpe
2018-08-09 20:57           ` Kit Chow
2018-08-09 21:11             ` Logan Gunthorpe
2018-08-09 21:47               ` Kit Chow
2018-08-09 22:40                 ` Jiang, Dave
2018-08-09 22:48                   ` Kit Chow
2018-08-09 22:50                     ` Logan Gunthorpe
2018-08-09 23:00                       ` Kit Chow
2018-08-10 16:02                         ` Kit Chow
2018-08-10 16:23                           ` Kit Chow
2018-08-10 16:24                             ` Logan Gunthorpe
2018-08-10 16:24                           ` Logan Gunthorpe
2018-08-10 16:31                             ` Dave Jiang
2018-08-10 16:33                               ` Logan Gunthorpe
2018-08-10 17:01                                 ` Dave Jiang
2018-08-10 17:15                                   ` Logan Gunthorpe
2018-08-10 17:46                                     ` Dave Jiang
2018-08-11  0:53                                       ` Kit Chow
2018-08-11  2:10                                         ` Logan Gunthorpe
2018-08-13 14:23                                           ` Kit Chow
2018-08-13 14:59                                             ` Robin Murphy
2018-08-13 15:21                                               ` Kit Chow
2018-08-13 23:30                                                 ` Kit Chow
2018-08-13 23:39                                                   ` Logan Gunthorpe
2018-08-13 23:48                                                     ` Kit Chow [this message]
2018-08-13 23:50                                                       ` Logan Gunthorpe
2018-08-14 13:47                                                         ` Kit Chow
2018-08-14 14:03                                                         ` Robin Murphy
2018-08-13 23:36                                                 ` Kit Chow
2018-08-09 21:31       ` Eric Pilmore
2018-08-09 21:36         ` Logan Gunthorpe
2018-08-16 17:16           ` Kit Chow
2018-08-16 17:21             ` Logan Gunthorpe
2018-08-16 18:53               ` Kit Chow
2018-08-16 18:56                 ` Logan Gunthorpe
2018-08-21 23:18                   ` Eric Pilmore
2018-08-21 23:20                     ` Logan Gunthorpe
2018-08-21 23:28                       ` Eric Pilmore
2018-08-21 23:35                         ` Logan Gunthorpe
2018-08-21 23:45                           ` Eric Pilmore
2018-08-21 23:53                             ` Logan Gunthorpe
2018-08-21 23:59                               ` Eric Pilmore
2018-08-21 23:30                       ` Eric Pilmore

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