[PATCH] lmb: prohibit allocations above ram_top even from same bank

[Sughosh Ganu]

On Fri, 13 Dec 2024 at 14:44, Patrice CHOTARD
<patrice.chotard at foss.st.com> wrote:
>
>
>
> On 12/12/24 20:50, Sughosh Ganu wrote:
> > On Fri, 13 Dec 2024 at 00:48, Tom Rini <trini at konsulko.com> wrote:
> >>
> >> On Wed, Dec 11, 2024 at 05:18:28PM +0100, Patrice CHOTARD wrote:
> >>
> >>>
> >>>
> >>> On 12/7/24 16:57, Tom Rini wrote:
> >>>> On Mon, 02 Dec 2024 12:36:24 +0530, Sughosh Ganu wrote:
> >>>>
> >>>>> There are platforms which set the value of ram_top based on certain
> >>>>> restrictions that the platform might have in accessing memory above
> >>>>> ram_top, even when the memory region is in the same DRAM bank. So,
> >>>>> even though the LMB allocator works as expected, when trying to
> >>>>> allocate memory above ram_top, prohibit this by marking all memory
> >>>>> above ram_top as reserved, even if the said memory region is from the
> >>>>> same bank.
> >>>>>
> >>>>> [...]
> >>>>
> >>>> Applied to u-boot/master, thanks!
> >>>>
> >>> Hello
> >>>
> >>> This patch is breaking the boot on STM32MP135F-DK.
> >>>
> >>> On this platform, we got an area above gd->ram_top,
> >>> this area, reserved for OPTEE, is tagged with LMB_NOMAP in boot_fdt_add_mem_rsv_regions().
> >>>
> >>> Since this commit 1a48b0be93d4 ("lmb: prohibit allocations above ram_top even from same bank"),
> >>> this area is no more tagged as LMB_NOMAP, because it's previously been
> >>> tagged with LMB_NOOVERWRITE in lmb_add_memory().
> >>>
> >>> By not being tagged LMB_NOMAP, the MMU configuration is impacted and leads to a panic.
> >>>
> >>> I suggest to revert this patch.
> >>
> >> Hi Patrice. Can you please re-test current top of tree? I believe Sam's
> >> series should resolve this problem as well. Thanks!
> >
> > Tom, that won't happen. This is a separate issue from what is being
> > fixed by Sam's series.
>
> Hi All
>
> I confirm, Sam's series didn't help here as Sughosh said.
>
> >
> > Patrice, please let me know if the hang is being fixed by the change
> > that I had suggested earlier in this thread. For some reason I don't
> > see a hang on the DK2 board despite the board having a similar memory
> > map of memory being reserved for the op-tee image above ram_top with
> > no-map property.
>
> On my side i didn't see the issue on STM32MP157C-DK2 board, but
> i got it systematically on STM2MP135F-DK.
>
> Your suggested patch is fixing the hang observed, i will send a patch.

Patrice, thanks much for testing and confirming the fix. I suspect
that the cpu's being used on the two boards might be different. Looks
like one implementation is speculatively prefetching data from the
op-tee memory region while other is not, which might explain why this
is not seen on all ST boards. Just a hunch though :)

-sughosh

>
> Thanks all ;-)
>
> Patrice
>
>
> >
> > -sughosh
> >
> >>
> >> --
> >> Tom