[coreboot-gerrit] New patch to review for coreboot: 182141e armv7: Change all memory domains to Client so XN bits work

[Patrick Georgi (pgeorgi@google.com)]

Patrick Georgi (pgeorgi at google.com) just uploaded a new patch set to gerrit, which you can find at http://review.coreboot.org/9343

-gerrit

commit 182141ee45812c2606bbcb74e20a878c78515244
Author: Julius Werner <jwerner at chromium.org>
Date:   Thu Oct 16 09:56:27 2014 -0700

    armv7: Change all memory domains to Client so XN bits work
    
    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
    Signed-off-by: Patrick Georgi <pgeorgi at chromium.org>
    Original-Commit-Id: cbc96db296a41ae700371a8515a1179c142f58e7
    Original-Change-Id: I30676a5bfe12d516e5f910f51ee6854f6e5be557
    Original-Signed-off-by: Julius Werner <jwerner at chromium.org>
    Original-Reviewed-on: https://chromium-review.googlesource.com/223783
    Original-Reviewed-by: Aaron Durbin <adurbin at chromium.org>
---
 src/arch/arm/armv7/mmu.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/src/arch/arm/armv7/mmu.c b/src/arch/arm/armv7/mmu.c
index de7fa40..581c572 100644
--- a/src/arch/arm/armv7/mmu.c
+++ b/src/arch/arm/armv7/mmu.c
@@ -302,6 +302,6 @@ void mmu_init(void)
 		0 << 16 | 0 << 0	/* Use TTBR0 for all addresses */
 		);
 
-	/* disable domain-level checking of permissions */
-	write_dacr(~0);
+	/* Set domain 0 to Client so XN bit works (to prevent prefetches) */
+	write_dacr(0x5);
 }