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From: Vlastimil Babka <vbabka@suse.cz>
To: Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc: Bjorn Andersson <bjorn.andersson@linaro.org>,
	Dmitry Torokhov <dmitry.torokhov@gmail.com>,
	Matt Fleming <matt@codeblueprint.co.uk>,
	Will Deacon <will.deacon@arm.com>,
	Michal Hocko <mhocko@kernel.org>,
	David Howells <dhowells@redhat.com>,
	David Brown <david.brown@linaro.org>,
	Peter Jones <pjones@redhat.com>,
	"Luis R. Rodriguez" <mcgrof@kernel.org>,
	"H . Peter Anvin" <hpa@zytor.com>,
	"open list:ANDROID DRIVERS" <devel@driverdev.osuosl.org>,
	Nicolas Broeking <nbroeking@me.com>,
	Jonathan Corbet <corbet@lwn.net>,
	the arch/x86 maintainers <x86@kernel.org>,
	Arve Hj?nnev?g <arve@android.com>, Ingo Molnar <mingo@redhat.com>,
	Kalle Valo <kvalo@codeaurora.org>,
	Andy Gross <andy.gross@linaro.org>,
	Darren Hart <dvhart@infradead.org>,
	Mimi Zohar <zohar@linux.vnet.ibm.com>,
	Arend Van Spriel <arend.vanspriel@broadcom.com>,
	Todd Kjos <tkjos@android.com>, Kees Cook <keescook@chromium.org>,
	linux-efi <linux-efi@vger.kernel.org>,
	Rik van Riel <riel@surriel.com>,
	linux-arm-msm@vger.kernel.org, Torsten Duwe <duwe@suse.de>,
	Josh Triplett <josh@joshtriplett.org>,
	Chris Wright <chrisw@sous-sol.org>,
	Hans de Goede <hdegoede@redhat.com>,
	Andy Lutomirski <luto@kernel.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	platform-driver-x86@vger.kernel.org,
	Martijn Coenen <maco@android.com>,
	Alan Cox <alan@linux.intel.com>,
	Martin Fuzzey <mfuzzey@parkeon.com>,
	Stephen Boyd <sboyd@kernel.org>,
	Vikram Mulukutla <markivx@codeaurora.org>,
	LKML <linux-kernel@vger.kernel.org>,
	linux-security-module <linux-security-module@vger.kernel.org>,
	Dave Olsthoorn <dave@bewaar.me>,
	Andrew Morton <akpm@linux-foundation.org>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	Andy Shevchenko <andy@infradead.org>
Subject: Re: Do Qualcomm drivers use DMA buffers for request_firmware_into_buf()?
Date: Fri, 8 Jun 2018 08:41:28 +0200	[thread overview]
Message-ID: <39e942b6-795c-b7c8-bf9d-16907ef40aea@suse.cz> (raw)
In-Reply-To: <20180607163308.GA18834@kroah.com>

On 06/07/2018 06:33 PM, Greg Kroah-Hartman wrote:
> On Thu, Jun 07, 2018 at 06:23:01PM +0200, Ard Biesheuvel wrote:
>> On 7 June 2018 at 18:18, Bjorn Andersson <bjorn.andersson@linaro.org> wrote:
>>> On Wed 06 Jun 13:32 PDT 2018, Luis R. Rodriguez wrote:
>>>
>>>> On Fri, Jun 01, 2018 at 09:23:46PM +0200, Luis R. Rodriguez wrote:
>>>>> On Tue, May 08, 2018 at 03:38:05PM +0000, Luis R. Rodriguez wrote:
>>>>>> On Fri, May 04, 2018 at 12:44:37PM -0700, Martijn Coenen wrote:
>>>>>>>
>>>>>>> I think the Qualcomm folks owning this (Andy, David, Bjorn, already
>>>>>>> cc'd here) are better suited to answer that question.
>>>>>>
>>>>>> Andy, David, Bjorn?
>>>>>
>>>>> Andy, David, Bjorn?
>>>>
>>>> A month now with no answer...
>>>>
>>>
>>> The patch at the top of this thread doesn't interest me and you didn't
>>> bother sending your question To me.
>>>
>>> As a matter of fact I'm confused to what the actual question is.
>>>
>>
>> The actual question is whether it is really required that the firmware
>> is loaded by the kernel into a buffer that is already mapped for DMA
>> at that point, and thus accessible by the device.
>>
>> To me, it is not entirely clear what the nature is of the firmware
>> that we are talking about, since it seems to be getting passed to the
>> secure world as well?
>>
>> In any case, the preferred model in terms of validation/sig checking is
>>
>> 1) allocate a CPU accessible buffer
>>
>> 2) request the firmware into it (which may include a sig check under the hood)
>>
>> 3) map the buffer for DMA to the device so it can load the firmware.
>>
>> 4) kick off the DMA transfer.
>>
>> The use of dma_alloc_coherent() for this purpose seems unnecessary,
>> given that the DMA transfer is not bidirectional. Would it be possible
>> to replace it with something like the above sequence?
> 
> Why not just use kmalloc, it will always return a DMAable buffer.

DMAble in what sense? For devices that can't handle physical addresses
above 16M you need to pass __GFP_DMA to get those, from ZONE_DMA.
Otherwise it can return anything from lowmem. That's for x86_64, some
other arches have different DMA zone.

> Is the problem that vmalloc() might not?

vmalloc() could only be used as an alternative if you used kvmalloc(),
otherwise kmalloc() won't give you anything from vmalloc

> We need to drop the whole DMA zone crud, it confuses everyone who sees
> it and was primarily for really really old systems.

Yeah that would be nice.

> greg k-h
> 

  parent reply	other threads:[~2018-06-08  6:41 UTC|newest]

Thread overview: 36+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-04-08 17:40 [PATCH v3 0/5] efi/firmware/platform-x86: Add EFI embedded fw support Hans de Goede
2018-04-08 17:40 ` [PATCH v3 1/5] efi: Export boot-services code and data as debugfs-blobs Hans de Goede
2018-04-16  8:23   ` Ard Biesheuvel
2018-04-24 13:11     ` Hans de Goede
2018-04-23 11:55   ` Greg Kroah-Hartman
2018-04-08 17:40 ` [PATCH v3 2/5] efi: Add embedded peripheral firmware support Hans de Goede
2018-04-16  8:28   ` Ard Biesheuvel
2018-04-24 13:17     ` Hans de Goede
2018-04-17  0:17   ` Luis R. Rodriguez
2018-04-17  8:58     ` Hans de Goede
2018-04-17  9:19     ` Hans de Goede
2018-04-23 21:11   ` Luis R. Rodriguez
2018-04-24 15:09     ` Hans de Goede
2018-04-24 16:07       ` Mimi Zohar
2018-04-24 18:33         ` Hans de Goede
2018-04-24 23:42         ` Luis R. Rodriguez
2018-04-25  5:00           ` Mimi Zohar
2018-04-25 17:55             ` Luis R. Rodriguez
2018-05-04  0:21               ` Luis R. Rodriguez
2018-05-04 15:26                 ` Martijn Coenen
2018-05-04 19:44               ` Martijn Coenen
2018-05-08 15:38                 ` Luis R. Rodriguez
2018-05-08 16:10                   ` Luis R. Rodriguez
2018-06-07 16:49                     ` Bjorn Andersson
2018-06-07 18:22                       ` Luis R. Rodriguez
2018-06-01 19:23                   ` Luis R. Rodriguez
2018-06-06 20:32                     ` Do Qualcomm drivers use DMA buffers for request_firmware_into_buf()? Luis R. Rodriguez
2018-06-07 16:18                       ` Bjorn Andersson
     [not found]                         ` <CAKv+Gu8+Fq7BD4XD-YCyXzZh0mg6Z2k-0styj0cw6_uZfaqy4Q@mail.gmail.com>
     [not found]                           ` <20180607163308.GA18834@kroah.com>
2018-06-08  6:41                             ` Vlastimil Babka [this message]
2018-06-07 16:33             ` [PATCH v3 2/5] efi: Add embedded peripheral firmware support Bjorn Andersson
2018-04-08 17:40 ` [PATCH v3 3/5] platform/x86: Rename silead_dmi to touchscreen_dmi Hans de Goede
2018-04-09  8:07   ` Andy Shevchenko
2018-04-20  0:20     ` Darren Hart
2018-04-08 17:40 ` [PATCH v3 4/5] platform/x86: touchscreen_dmi: Add EFI embedded firmware info support Hans de Goede
2018-04-08 17:40 ` [PATCH v3 5/5] platform/x86: touchscreen_dmi: Add info for the Chuwi Vi8 Plus tablet Hans de Goede
2018-04-09  8:10   ` Andy Shevchenko

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