[kvm-unit-tests PATCH 2/4] arm/arm64: Read system registers to get the state of the MMU

[Nikos Nikoleris <nikos.nikoleris@arm.com>]

When we are in EL1 we can directly tell if the local cpu's MMU is on
by reading a system register (SCTRL/SCTRL_EL1). In EL0, we use the
relevant cpumask. This way we don't have to rely on the cpu id in
thread_info when we are in setup executing in EL1. In subsequent
patches we resolve the problem of identifying safely whether we are
executing in EL1 or EL0.

Signed-off-by: Nikos Nikoleris <nikos.nikoleris@arm.com>
---
 lib/arm/asm/mmu-api.h     |  7 +------
 lib/arm/asm/processor.h   |  7 +++++++
 lib/arm64/asm/processor.h |  1 +
 lib/arm/mmu.c             | 16 ++++++++--------
 lib/arm/processor.c       |  5 +++++
 lib/arm64/processor.c     |  5 +++++
 6 files changed, 27 insertions(+), 14 deletions(-)

diff --git a/lib/arm/asm/mmu-api.h b/lib/arm/asm/mmu-api.h
index 3d04d03..05fc12b 100644
--- a/lib/arm/asm/mmu-api.h
+++ b/lib/arm/asm/mmu-api.h
@@ -5,12 +5,7 @@
 #include <stdbool.h>
 
 extern pgd_t *mmu_idmap;
-extern unsigned int mmu_disabled_cpu_count;
-extern bool __mmu_enabled(void);
-static inline bool mmu_enabled(void)
-{
-	return mmu_disabled_cpu_count == 0 || __mmu_enabled();
-}
+extern bool mmu_enabled(void);
 extern void mmu_mark_enabled(int cpu);
 extern void mmu_mark_disabled(int cpu);
 extern void mmu_enable(pgd_t *pgtable);
diff --git a/lib/arm/asm/processor.h b/lib/arm/asm/processor.h
index 273366d..af54c09 100644
--- a/lib/arm/asm/processor.h
+++ b/lib/arm/asm/processor.h
@@ -67,11 +67,13 @@ extern int mpidr_to_cpu(uint64_t mpidr);
 	((mpidr >> MPIDR_LEVEL_SHIFT(level)) & 0xff)
 
 extern void start_usr(void (*func)(void *arg), void *arg, unsigned long sp_usr);
+extern bool __mmu_enabled(void);
 extern bool is_user(void);
 
 #define CNTVCT		__ACCESS_CP15_64(1, c14)
 #define CNTFRQ		__ACCESS_CP15(c14, 0, c0, 0)
 #define CTR		__ACCESS_CP15(c0, 0, c0, 1)
+#define SCTRL		__ACCESS_CP15(c1, 0, c0, 0)
 
 static inline u64 get_cntvct(void)
 {
@@ -89,6 +91,11 @@ static inline u32 get_ctr(void)
 	return read_sysreg(CTR);
 }
 
+static inline u32 get_sctrl(void)
+{
+	return read_sysreg(SCTRL);
+}
+
 extern unsigned long dcache_line_size;
 
 #endif /* _ASMARM_PROCESSOR_H_ */
diff --git a/lib/arm64/asm/processor.h b/lib/arm64/asm/processor.h
index 771b2d1..8e2037e 100644
--- a/lib/arm64/asm/processor.h
+++ b/lib/arm64/asm/processor.h
@@ -98,6 +98,7 @@ extern int mpidr_to_cpu(uint64_t mpidr);
 
 extern void start_usr(void (*func)(void *arg), void *arg, unsigned long sp_usr);
 extern bool is_user(void);
+extern bool __mmu_enabled(void);
 
 static inline u64 get_cntvct(void)
 {
diff --git a/lib/arm/mmu.c b/lib/arm/mmu.c
index a1862a5..d806c63 100644
--- a/lib/arm/mmu.c
+++ b/lib/arm/mmu.c
@@ -24,10 +24,9 @@ extern unsigned long etext;
 pgd_t *mmu_idmap;
 
 /* CPU 0 starts with disabled MMU */
-static cpumask_t mmu_disabled_cpumask = { {1} };
-unsigned int mmu_disabled_cpu_count = 1;
+static cpumask_t mmu_enabled_cpumask = { {0} };
 
-bool __mmu_enabled(void)
+bool mmu_enabled(void)
 {
 	int cpu = current_thread_info()->cpu;
 
@@ -38,19 +37,20 @@ bool __mmu_enabled(void)
 	 * spinlock, atomic bitop, etc., otherwise we'll recurse.
 	 * [cpumask_]test_bit is safe though.
 	 */
-	return !cpumask_test_cpu(cpu, &mmu_disabled_cpumask);
+	if (is_user())
+		return cpumask_test_cpu(cpu, &mmu_enabled_cpumask);
+	else
+		return __mmu_enabled();
 }
 
 void mmu_mark_enabled(int cpu)
 {
-	if (cpumask_test_and_clear_cpu(cpu, &mmu_disabled_cpumask))
-		--mmu_disabled_cpu_count;
+	cpumask_set_cpu(cpu, &mmu_enabled_cpumask);
 }
 
 void mmu_mark_disabled(int cpu)
 {
-	if (!cpumask_test_and_set_cpu(cpu, &mmu_disabled_cpumask))
-		++mmu_disabled_cpu_count;
+	cpumask_clear_cpu(cpu, &mmu_enabled_cpumask);
 }
 
 extern void asm_mmu_enable(phys_addr_t pgtable);
diff --git a/lib/arm/processor.c b/lib/arm/processor.c
index 773337e..a2d39a4 100644
--- a/lib/arm/processor.c
+++ b/lib/arm/processor.c
@@ -145,3 +145,8 @@ bool is_user(void)
 {
 	return current_thread_info()->flags & TIF_USER_MODE;
 }
+
+bool __mmu_enabled(void)
+{
+	return get_sctrl() & CR_M;
+}
diff --git a/lib/arm64/processor.c b/lib/arm64/processor.c
index 2a024e3..ef55862 100644
--- a/lib/arm64/processor.c
+++ b/lib/arm64/processor.c
@@ -257,3 +257,8 @@ bool is_user(void)
 {
 	return current_thread_info()->flags & TIF_USER_MODE;
 }
+
+bool __mmu_enabled(void)
+{
+	return read_sysreg(sctlr_el1) & SCTLR_EL1_M;
+}
-- 
2.25.1