[PATCH 01/10] board: ti: am62x: Init DRAM size in R5/A53 SPL

[Tom Rini]

On Tue, Apr 16, 2024 at 05:52:58PM +0530, Chintan Vankar wrote:
> 
> 
> On 12/04/24 03:37, Tom Rini wrote:
> > On Wed, Apr 03, 2024 at 06:18:01PM +0530, Chintan Vankar wrote:
> > > 
> > > 
> > > On 22/01/24 10:11, Siddharth Vadapalli wrote:
> > > > 
> > > > 
> > > > On 20/01/24 22:11, Tom Rini wrote:
> > > > > On Mon, Jan 15, 2024 at 01:42:51PM +0530, Siddharth Vadapalli wrote:
> > > > > > Hello Tom,
> > > > > > 
> > > > > > On 12/01/24 18:56, Tom Rini wrote:
> > > > 
> > > > ...
> > > > 
> > > > > > > The list of conditionals in common/spl/spl.c::board_init_r() should be
> > > > > > > updated and probably use SPL_NET as the option to check for.
> > > > > > 
> > > > > > Thank you for reviewing the patch and pointing this out. I wasn't aware of it. I
> > > > > > assume that you are referring to the following change:
> > > > > > 
> > > > > >           if (IS_ENABLED(CONFIG_SPL_OS_BOOT) || CONFIG_IS_ENABLED(HANDOFF) ||
> > > > > > -           IS_ENABLED(CONFIG_SPL_ATF))
> > > > > > +           IS_ENABLED(CONFIG_SPL_ATF) || IS_ENABLED(CONFIG_SPL_NET))
> > > > > >                   dram_init_banksize();
> > > > > > 
> > > > > > I shall replace the current patch with the above change in the v2 series. Since
> > > > > > this is in the common section, is there a generic reason I could provide in the
> > > > > > commit message rather than the existing commit message which seems to be board
> > > > > > specific? Also, I hope that the above change will not cause regressions for
> > > > > > other non-TI devices. Please let me know.
> > > > > 
> > > > > Yes, that's the area, and just note that networking also requires the
> > > > > DDR to be initialized.
> > > > > 
> > > > 
> > > > Thank you for confirming and providing your suggestion for the contents of the
> > > > commit message.
> > > > 
> > > Following Tom's Suggestion of adding CONFIG_SPL_NET in common/spl/spl.c
> > > "dram_init_banksize()", the issue of fetching a file at SPL stage seemed
> > > to be fixed. However the commit "ba20b2443c29", which sets gd->ram_top
> > > for the very first time in "spl_enable_cache()" results in
> > > "arch_lmb_reserve()" function reserving memory region from Stack pointer
> > > at "0x81FFB820" to gd->ram_top pointing to "0x100000000". Previously
> > > when gd->ram_top was zero "arch_lmb_reserve()" was noop. Now using TFTP
> > > to fetch U-Boot image at SPL stage results in "tftp_init_load_addr()"
> > > function call that invokes "arch_lmb_reserve()" function, which reserves
> > > entire memory starting from Stack Pointer to gd->ram_top leaving no
> > > space to load U-Boot image via TFTP since TFTP loads files at pre
> > > configured memory address at "0x82000000".
> > > 
> > > As a workaround for this issue, one solution we can propose is to
> > > disable the checks "lmb_get_free_size()" at SPL and U-Boot stage. For
> > > that we can define a new config option for LMB reserve checks as
> > > "SPL_LMB". This config will be enable by default for the backword
> > > compatibility and disable for our use case at SPL and U-Boot stage.
> > 
> > The problem here is that we need LMB for booting an OS, which is
> > something we'll want in SPL in non-cortex-R cases too, which means this
> > platform, so that's a no-go. I think you need to dig harder and see if
> > you can correct the logic somewhere so that we don't over reserve?
> > 
> Since this issue is due to function call "lmb_init_and_reserve()"
> function invoked from "tftp_init_load_addr()" function. This function
> is defined by Simon in commit "a156c47e39ad", which fixes
> "CVE-2018-18439" to prevent overwriting reserved memory. Simon, can you
> explain why do we need to call "lmb_init_and_reserve()" function here ?

This is indeed a tricky area which is why Sughosh is looking in to
trying to re-work the LMB mechanic and we've had a few long threads
about it as well.

I've honestly forgotten the use case you have here, can you please
remind us?

-- 
Tom
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