Re: [PATCH V4 6/6] PCI: rcar: Fix 64bit MSI message address handling

[Marek Vasut <marek.vasut@gmail.com>]

On 3/27/19 1:22 PM, Geert Uytterhoeven wrote:
> On Wed, Mar 27, 2019 at 12:30 PM Simon Horman <horms@verge.net.au> wrote:
>> On Mon, Mar 25, 2019 at 12:41:01PM +0100, marek.vasut@gmail.com wrote:
>>> From: Marek Vasut <marek.vasut+renesas@gmail.com>
>>> The MSI message address in the RC address space can be 64 bit. The
>>> R-Car PCIe RC supports such a 64bit MSI message address as well.
>>> The code currently uses virt_to_phys(__get_free_pages()) to obtain
>>> a reserved page for the MSI message address, and the return value
>>> of which can be a 64 bit physical address on 64 bit system.
>>>
>>> However, the driver only programs PCIEMSIALR register with the bottom
>>> 32 bits of the virt_to_phys(__get_free_pages()) return value and does
>>> not program the top 32 bits into PCIEMSIAUR, but rather programs the
>>> PCIEMSIAUR register with 0x0. This worked fine on older 32 bit R-Car
>>> SoCs, however may fail on new 64 bit R-Car SoCs.
>>>
>>> Since from a PCIe controller perspective, an inbound MSI is a memory
>>> write to a special address (in case of this controller, defined by
>>> the value in PCIEMSIAUR:PCIEMSIALR), which triggers an interrupt, but
>>> never hits the DRAM _and_ because allocation of an MSI by a PCIe card
>>> driver obtains the MSI message address by reading PCIEMSIAUR:PCIEMSIALR
>>> in rcar_msi_setup_irqs(), incorrectly programmed PCIEMSIAUR cannot
>>> cause memory corruption or other issues.
>>>
>>> There is however the possibility that if virt_to_phys(__get_free_pages())
>>> returned address above the 32bit boundary _and_ PCIEMSIAUR was programmed
>>> to 0x0 _and_ if the system had physical RAM at the address matching the
>>> value of PCIEMSIALR, a PCIe card driver could allocate a buffer with a
>>> physical address matching the value of PCIEMSIALR and a remote write to
>>> such a buffer by a PCIe card would trigger a spurious MSI.
>>>
>>> Signed-off-by: Marek Vasut <marek.vasut+renesas@gmail.com>
>>> Cc: Geert Uytterhoeven <geert+renesas@glider.be>
>>> Cc: Phil Edworthy <phil.edworthy@renesas.com>
>>> Cc: Simon Horman <horms+renesas@verge.net.au>
>>> Cc: Wolfram Sang <wsa@the-dreams.de>
>>> Cc: linux-renesas-soc@vger.kernel.org
>>> To: linux-pci@vger.kernel.org
>>> Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
>>
>> Does this warrant a Fixes tag?
> 
> (digging in old sent email)
> Fixes: 290c1fb358605402 ("PCI: rcar: Add MSI support for PCIe")

But does it really fix that commit, given that on Gen2 and earlier, it
was not broken as those were 32bit platforms ?

-- 
Best regards,
Marek Vasut