Re: [PATCH V3 6/6] PCI: rcar: Fix 64bit MSI message address handling

[Geert Uytterhoeven <geert@linux-m68k.org>]

On Sat, Mar 23, 2019 at 2:54 AM <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>

Thanks for the nice explanation!

Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

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