On Mon May 18, 2026 at 1:34 PM IST, Ilias Apalodimas wrote:
> Hi Anshul
>
> On Tue, 12 May 2026 at 14:03, Anshul Dalal <[email protected]> wrote:
>>
>> Currently the sequence to enable caches for the A53/A72 core on K3
>> devices looks as follows:
>>
>> 1. Map entire DDR banks
>> 2. Setup page tables and enable MMU (done by mmu_setup)
>> 3. Unmap reserved-memory regions
>> 4. Enable caches
>>
>> However there is a brief period of execution between #2 and #3 where the
>> core can issue speculative accesses to the entire DDR space (including
>> the reserved-memory regions) despite the caches being disabled.
>
> This is indeed a problem and the fix looks correct.
> What worries me though is that the mmu is common across v8 boards. Is
> there a way to generalize this instead of adding per board variants?
>
I think the issue here is that mmu_setup does two things, first it sets
up the page tables and then it enables the MMU right after that.
We could modify mmu_setup so that it only does the former as follows:
--- a/arch/arm/cpu/armv8/cache_v8.c
+++ b/arch/arm/cpu/armv8/cache_v8.c
@@ -801,20 +801,20 @@ static void setup_all_pgtables(void)
/* to activate the MMU we need to set up virtual memory */
__weak void mmu_setup(void)
{
int el;
+ /* disable the mmu */
+ set_sctlr(get_sctlr() & ~CR_M);
+
/* Set up page tables only once */
if (!gd->arch.tlb_fillptr)
setup_all_pgtables();
el = current_el();
set_ttbr_tcr_mair(el, gd->arch.tlb_addr, get_tcr(NULL, NULL),
MEMORY_ATTRIBUTES);
-
- /* enable the mmu */
- set_sctlr(get_sctlr() | CR_M);
}
Then we can have an `mmu_enable` to explicitly enable the MMU:
void mmu_enable(void) {
/* enable the mmu */
set_sctlr(get_sctlr() | CR_M);
}
Regards,
Anshul
>
>>
>> A firewall exception is triggered whenever such speculative access is
>> made to secure DDR region of TFA or OP-TEE. This patch fixes the issue
>> by re-ordering the sequence as follows:
>>
>> 1. Map entire DDR banks
>> 2. Setup page tables
>> 3. Unmap reserved-memory regions
>> 4. Enable MMU
>> 5. Enable caches
>>
>> Fixes: f1c694b8fdde ("mach-k3: map all banks using mem_map_from_dram_banks")
>> Signed-off-by: Anshul Dalal <[email protected]>
>> ---
[snip]
