From: Russell King - ARM Linux admin <linux@armlinux.org.uk>
To: Greg KH <gregkh@linuxfoundation.org>
Cc: yvahkhfo.1df7f8c2@hashmail.org, security@kernel.org,
linux-usb@vger.kernel.org, linux-arm-kernel@lists.infradead.org
Subject: Re: usb zero copy dma handling
Date: Thu, 8 Aug 2019 10:59:51 +0100 [thread overview]
Message-ID: <20190808095951.GD5193@shell.armlinux.org.uk> (raw)
In-Reply-To: <20190808085811.GA1265@kroah.com>
On Thu, Aug 08, 2019 at 10:58:11AM +0200, Greg KH wrote:
> But the main issue here is what exactly is this "fixing"? What is wrong
> with the existing code that non-x86 systems have such a problem with?
> Shouldn't all of these dma issues be handled by the platform with the
> remap_pfn_range() call itself?
remap_pfn_range() takes a PFN. virt_to_phys() converts a kernel *direct
mapped* virtual address to a physical address. That much is fine.
The question is - what is usbm->mem? If that is anything other than an
address returned by kmalloc() or from the normal page allocator, then
virt_to_phys() will return garbage.
In other words, if it comes from dma_alloc_coherent(), vmalloc() or
ioremap(), using virt_to_phys() on it results in garbage.
This aspect of virt_to_phys() has been well known about for ages; it's
one of the fundamentals of kernel programming.
--
RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
FTTC broadband for 0.8mile line in suburbia: sync at 12.1Mbps down 622kbps up
According to speedtest.net: 11.9Mbps down 500kbps up
WARNING: multiple messages have this Message-ID (diff)
From: Russell King - ARM Linux admin <linux@armlinux.org.uk>
To: Greg KH <gregkh@linuxfoundation.org>
Cc: yvahkhfo.1df7f8c2@hashmail.org, linux-usb@vger.kernel.org,
security@kernel.org, linux-arm-kernel@lists.infradead.org
Subject: Re: usb zero copy dma handling
Date: Thu, 8 Aug 2019 10:59:51 +0100 [thread overview]
Message-ID: <20190808095951.GD5193@shell.armlinux.org.uk> (raw)
In-Reply-To: <20190808085811.GA1265@kroah.com>
On Thu, Aug 08, 2019 at 10:58:11AM +0200, Greg KH wrote:
> But the main issue here is what exactly is this "fixing"? What is wrong
> with the existing code that non-x86 systems have such a problem with?
> Shouldn't all of these dma issues be handled by the platform with the
> remap_pfn_range() call itself?
remap_pfn_range() takes a PFN. virt_to_phys() converts a kernel *direct
mapped* virtual address to a physical address. That much is fine.
The question is - what is usbm->mem? If that is anything other than an
address returned by kmalloc() or from the normal page allocator, then
virt_to_phys() will return garbage.
In other words, if it comes from dma_alloc_coherent(), vmalloc() or
ioremap(), using virt_to_phys() on it results in garbage.
This aspect of virt_to_phys() has been well known about for ages; it's
one of the fundamentals of kernel programming.
--
RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
FTTC broadband for 0.8mile line in suburbia: sync at 12.1Mbps down 622kbps up
According to speedtest.net: 11.9Mbps down 500kbps up
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next prev parent reply other threads:[~2019-08-08 10:00 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-08-08 8:46 usb zero copy dma handling yvahkhfo.1df7f8c2
2019-08-08 8:46 ` yvahkhfo.1df7f8c2
2019-08-08 8:58 ` Greg KH
2019-08-08 8:58 ` Greg KH
2019-08-08 9:46 ` Robin Murphy
2019-08-08 9:46 ` Robin Murphy
2019-08-08 10:07 ` Greg KH
2019-08-08 10:07 ` Greg KH
2019-08-08 10:43 ` Robin Murphy
2019-08-08 10:43 ` Robin Murphy
2019-08-08 13:05 ` Greg KH
2019-08-08 13:05 ` Greg KH
2019-08-08 9:59 ` Russell King - ARM Linux admin [this message]
2019-08-08 9:59 ` Russell King - ARM Linux admin
2019-08-08 10:02 ` Oliver Neukum
2019-08-08 10:02 ` Oliver Neukum
2019-08-08 16:10 ` Christoph Hellwig
2019-08-08 16:10 ` Christoph Hellwig
2019-08-08 16:12 ` Christoph Hellwig
2019-08-08 16:12 ` Christoph Hellwig
2019-08-08 16:57 ` Russell King - ARM Linux admin
2019-08-08 16:57 ` Russell King - ARM Linux admin
-- strict thread matches above, loose matches on Subject: below --
2019-07-27 13:57 yvahknez.7f7d2ff0
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