When the MMU is off, data accesses are to Device nGnRnE memory on arm64 [1]
or to Strongly-Ordered memory on arm [2]. This means that the accesses are
non-cacheable.
Perform a dcache clean to PoC so we can read the newer values from the
cache, instead of the stale values from memory.
Perform an invalidation so when we re-enable the MMU, we can access the
data written to memory while the MMU was off, instead of potentially stale
values from the cache.
Data caches are PIPT and the VAs are translated using the current
translation tables, or an identity mapping (what Arm calls a "flat
mapping") when the MMU is off [1], [2]. Do the clean + invalidate when the
MMU is off so we don't depend on the current translation tables and we can
make sure that the operation applies to the entire physical memory.
[1] ARM DDI 0487E.a, section D5.2.9
[2] ARM DDI 0406C.d, section B3.2.1
Signed-off-by: Alexandru Elisei <alexandru.elisei@xxxxxxx>
---
Tested with the following hack:
diff --git a/arm/selftest.c b/arm/selftest.c
index e9dc5c0cab28..7f29548bc468 100644
--- a/arm/selftest.c
+++ b/arm/selftest.c
@@ -350,10 +350,21 @@ static void cpu_report(void *data __unused)
report_info("CPU%3d: MPIDR=%010" PRIx64, cpu, mpidr);
}
+#include <alloc_page.h>
+#include <asm/mmu.h>
int main(int argc, char **argv)
{
+ int *x = alloc_page();
+
report_prefix_push("selftest");
+ *x = 0x42;
+ mmu_disable();
+ report("read back value written with MMU on", *x == 0x42);
+ *x = 0x50;
+ mmu_enable(current_thread_info()->pgtable);
+ report("read back value written with MMU off", *x == 0x50);
+
if (argc < 2)
report_abort("no test specified");
Without the fix, the first report fails, and the test usually hangs because
mmu_enable pushes the LR register on the stack before asm_mmu_enable, which
goes to memory, then pops it after asm_mmu_enable, and reads back garbage
from the dcache.
With the fix, the two reports pass.
lib/arm/asm/processor.h | 6 ++++++
lib/arm64/asm/processor.h | 6 ++++++
lib/arm/processor.c | 10 ++++++++++
lib/arm/setup.c | 2 ++
lib/arm64/processor.c | 11 +++++++++++
arm/cstart.S | 22 ++++++++++++++++++++++
arm/cstart64.S | 23 +++++++++++++++++++++++
7 files changed, 80 insertions(+)
diff --git a/lib/arm/asm/processor.h b/lib/arm/asm/processor.h
index a8c4628da818..4684fb4755b3 100644
--- a/lib/arm/asm/processor.h
+++ b/lib/arm/asm/processor.h
@@ -9,6 +9,11 @@
#include <asm/sysreg.h>
#include <asm/barrier.h>
+#define CTR_DMINLINE_SHIFT 16
+#define CTR_DMINLINE_MASK (0xf << 16)
+#define CTR_DMINLINE(x) \
+ (((x) & CTR_DMINLINE_MASK) >> CTR_DMINLINE_SHIFT)
+
enum vector {
EXCPTN_RST,
EXCPTN_UND,
@@ -25,6 +30,7 @@ typedef void (*exception_fn)(struct pt_regs *);
extern void install_exception_handler(enum vector v, exception_fn fn);
extern void show_regs(struct pt_regs *regs);
+extern void init_dcache_line_size(void);
static inline unsigned long current_cpsr(void)
{
diff --git a/lib/arm64/asm/processor.h b/lib/arm64/asm/processor.h
index 1d9223f728a5..fd508c02f30d 100644
--- a/lib/arm64/asm/processor.h
+++ b/lib/arm64/asm/processor.h
@@ -16,6 +16,11 @@
#define SCTLR_EL1_A (1 << 1)
#define SCTLR_EL1_M (1 << 0)
+#define CTR_EL0_DMINLINE_SHIFT 16
+#define CTR_EL0_DMINLINE_MASK (0xf << 16)
+#define CTR_EL0_DMINLINE(x) \
+ (((x) & CTR_EL0_DMINLINE_MASK) >> CTR_EL0_DMINLINE_SHIFT)
+
#ifndef __ASSEMBLY__
#include <asm/ptrace.h>
#include <asm/esr.h>
@@ -60,6 +65,7 @@ extern void vector_handlers_default_init(vector_fn *handlers);
extern void show_regs(struct pt_regs *regs);
extern bool get_far(unsigned int esr, unsigned long *far);
+extern void init_dcache_line_size(void);
static inline unsigned long current_level(void)
{
diff --git a/lib/arm/processor.c b/lib/arm/processor.c
index 773337e6d3b7..c57657c5ea53 100644
--- a/lib/arm/processor.c
+++ b/lib/arm/processor.c
@@ -25,6 +25,8 @@ static const char *vector_names[] = {
"rst", "und", "svc", "pabt", "dabt", "addrexcptn", "irq", "fiq"
};
+unsigned int dcache_line_size;
+
void show_regs(struct pt_regs *regs)
{
unsigned long flags;
@@ -145,3 +147,11 @@ bool is_user(void)
{
return current_thread_info()->flags & TIF_USER_MODE;
}
+void init_dcache_line_size(void)
+{
+ u32 ctr;
+
+ asm volatile("mrc p15, 0, %0, c0, c0, 1" : "=r" (ctr));
+ /* DminLine is log2 of the number of words in the smallest cache line */
+ dcache_line_size = 1 << (CTR_DMINLINE(ctr) + 2);
+}
diff --git a/lib/arm/setup.c b/lib/arm/setup.c
index 4f02fca85607..54fc19a20942 100644
--- a/lib/arm/setup.c
+++ b/lib/arm/setup.c
@@ -20,6 +20,7 @@
#include <asm/thread_info.h>
#include <asm/setup.h>
#include <asm/page.h>
+#include <asm/processor.h>
#include <asm/smp.h>
#include "io.h"
@@ -63,6 +64,7 @@ static void cpu_init(void)
ret = dt_for_each_cpu_node(cpu_set, NULL);
assert(ret == 0);
set_cpu_online(0, true);
+ init_dcache_line_size();
}
static void mem_init(phys_addr_t freemem_start)
diff --git a/lib/arm64/processor.c b/lib/arm64/processor.c
index 2a024e3f4e9d..f28066d40145 100644
--- a/lib/arm64/processor.c
+++ b/lib/arm64/processor.c
@@ -62,6 +62,8 @@ static const char *ec_names[EC_MAX] = {
[ESR_EL1_EC_BRK64] = "BRK64",
};
+unsigned int dcache_line_size;
+
void show_regs(struct pt_regs *regs)
{
int i;
@@ -257,3 +259,12 @@ bool is_user(void)
{
return current_thread_info()->flags & TIF_USER_MODE;
}
+
+void init_dcache_line_size(void)
+{
+ u64 ctr;
+
+ ctr = read_sysreg(ctr_el0);
+ /* DminLine is log2 of the number of words in the smallest cache line */
+ dcache_line_size = 1 << (CTR_EL0_DMINLINE(ctr) + 2);
+}
diff --git a/arm/cstart.S b/arm/cstart.S
index dfef48e4dbb2..3c2a3bcde61a 100644
--- a/arm/cstart.S
+++ b/arm/cstart.S
@@ -188,6 +188,20 @@ asm_mmu_enable:
mov pc, lr
+.macro dcache_clean_inval domain, start, end, tmp1, tmp2
+ ldr \tmp1, =dcache_line_size
+ ldr \tmp1, [\tmp1]
+ sub \tmp2, \tmp1, #1
+ bic \start, \start, \tmp2
+9998:
+ /* DCCIMVAC */
+ mcr p15, 0, \start, c7, c14, 1
+ add \start, \start, \tmp1
+ cmp \start, \end
+ blo 9998b
+ dsb \domain
+.endm
+
.globl asm_mmu_disable
asm_mmu_disable:
/* SCTLR */
@@ -195,6 +209,14 @@ asm_mmu_disable:
bic r0, #CR_M
mcr p15, 0, r0, c1, c0, 0
isb
+
+ ldr r0, =__phys_offset
+ ldr r0, [r0]
+ ldr r1, =__phys_end
+ ldr r1, [r1]
+ dcache_clean_inval sy, r0, r1, r2, r3
+ isb
+
mov pc, lr
/*
diff --git a/arm/cstart64.S b/arm/cstart64.S
index c98842f11e90..f41ffa3bc6c2 100644
--- a/arm/cstart64.S
+++ b/arm/cstart64.S
@@ -201,12 +201,35 @@ asm_mmu_enable:
ret
+/* Taken with small changes from arch/arm64/incluse/asm/assembler.h */
+.macro dcache_by_line_op op, domain, start, end, tmp1, tmp2
+ adrp \tmp1, dcache_line_size
+ ldr \tmp1, [\tmp1, :lo12:dcache_line_size]
+ sub \tmp2, \tmp1, #1
+ bic \start, \start, \tmp2
+9998:
+ dc \op , \start
+ add \start, \start, \tmp1
+ cmp \start, \end
+ b.lo 9998b
+ dsb \domain
+.endm
+
.globl asm_mmu_disable
asm_mmu_disable:
mrs x0, sctlr_el1
bic x0, x0, SCTLR_EL1_M
msr sctlr_el1, x0
isb
+
+ /* Clean + invalidate the entire memory */
+ adrp x0, __phys_offset
+ ldr x0, [x0, :lo12:__phys_offset]
+ adrp x1, __phys_end
+ ldr x1, [x1, :lo12:__phys_end]
+ dcache_by_line_op civac, sy, x0, x1, x2, x3
+ isb
+
ret
/*
--
2.20.1
