armv7: Change all memory domains to Client so XN bits work

Hardware / Coreboot - Julius Werner [chromium.org] - 8 April 2015 02:27 UTC

Remember the XN bit? The one we had so much fun with on Nyan (LPAE) because not setting it allows random instruction prefetches to device memory that hang the system every few thousand boots? Thankfully, we had always been setting it in the non-LPAE MMU code already...

"When the XN bit is 1, a Permission fault is generated if the processor attempts to execute an instruction fetched from the corresponding memory region. However, when using the Short-descriptor translation table format, the fault is generated only if the access is to memory in the Client domain, see Domains[...]" - ARM A.R.M. section B3.7.2

Oops. This patch changes our Domain Access Control Register (DACR) to set domain 0 (the only one we are using) to Client. This means that access permissions (AP[2:0] bits) become enforced, but they are already set to full access (0b011). It also means that non-LPAE systems will not be allowed to execute from DCACHE_OFF memory with enabled MMU anymore. As far as I can see, Veyron_Pinky has been the only board that does that.

BUG=chrome-os-partner:32118 TEST=Booted Veyron_Pinky with MMU in the bootblock, saw hangs that look like spurious prefetches and confirmed that this patch fixes them.

Change-Id: I81c00743f938924a5dc8825389fe512a069b77db

ba11d6f armv7: Change all memory domains to Client so XN bits work
src/arch/arm/armv7/mmu.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)

Upstream: review.coreboot.org

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