On Fri, Mar 19, 2021 at 12:24:10PM +0000, Nikos Nikoleris wrote:
> Prior to this set of fixes, the code in setup() which we call to
> initialize the system has a circular dependency. cpu_init()
> (eventually) calls spin_lock() and __mmu_enabled(). However, at this
> point, __mmu_enabled() may have undefined behavior as we haven't
> initialized the current thread_info (cpu field). Moving
> thread_info_init() above cpu_init() is not possible as it relies on
> mpidr_to_cpu() which won't return the right results before cpu_init().
> In addition, mem_init() also calls __mmu_enabled() and therefore
> suffers from the same problem. Right now, everything works as
> thread_info maps to memory which is implicitly initialized to 0 (cpu =
> 0) and makes the assumption that the cpu that runs setup() will be the
> first cpu in the DT.
>
> This set of patches changes the code slightly and avoids this
> assumptions. In addition, it adds assertions to catch problems like
> the above. The current solution relies on the thread_info() of the cpu
> that setup() run to be initialized to zero (should we make it
> explicit?).
>
> There are a couple of options I considered in addressing this issue
> which didn't seem satisfactory:
>
> - Change the mmu_disabled_count global variable to mmu_enabled_count
> to count the number of active mmu's and bypass __mmu_enabled() when
> it's 0. This is a global variable and at the momement all write to
> it are protected by a lock but it's rather fragile and could easily
> cause issues in the future.
> - Explicitly initialize current_thread_info()->cpu = 0 in setup()
> before anything else or make the first call of thread_info_init() a
> special case and avoid looking up mpidr_to_cpu(). This way we can
> move thread_info_init() to the top of setup(). If the CPU setup is
> running on is not the first that appears in the DT then this
> solution won't work.
>
> Thanks,
>
> Nikos
>
> Nikos Nikoleris (4):
> arm/arm64: Avoid calling cpumask_test_cpu for CPUs above nr_cpu
> arm/arm64: Read system registers to get the state of the MMU
> arm/arm64: Track whether thread_info has been initialized
> arm/arm64: Add sanity checks to the cpumask API
>
> lib/arm/asm/cpumask.h | 7 ++++++-
> lib/arm/asm/mmu-api.h | 7 +------
> lib/arm/asm/processor.h | 7 +++++++
> lib/arm/asm/thread_info.h | 1 +
> lib/arm64/asm/processor.h | 1 +
> lib/arm/mmu.c | 16 ++++++++--------
> lib/arm/processor.c | 10 ++++++++--
> lib/arm64/processor.c | 10 ++++++++--
> 8 files changed, 40 insertions(+), 19 deletions(-)
>
> --
> 2.25.1
>
Hi Nikos,
So, I like patches 1, 2, and 4. I think 3 can be dropped with the
addition of "arm/arm64: Zero BSS and stack at startup". Would you
agree? I've applied all the updated commit messages and all of
Alexandru's suggestions to 2. Patch 2 now looks like the diff below.
Alexandru, are you satisfied with 1, 2, and 4? If so, please let me
know and I'll add r-b's for you before queuing.
Thanks,
drew
diff --git a/lib/arm/asm/mmu-api.h b/lib/arm/asm/mmu-api.h
index 3d04d0312622..05fc12b5afb8 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 273366d1fe1c..6b762ad060eb 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)
{
diff --git a/lib/arm/mmu.c b/lib/arm/mmu.c
index a1862a55db8b..15eef007f256 100644
--- a/lib/arm/mmu.c
+++ b/lib/arm/mmu.c
@@ -24,13 +24,10 @@ 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;
-bool __mmu_enabled(void)
+bool mmu_enabled(void)
{
- int cpu = current_thread_info()->cpu;
-
/*
* mmu_enabled is called from places that are guarding the
* use of exclusive ops (which require the mmu to be enabled).
@@ -38,19 +35,22 @@ 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()) {
+ int cpu = current_thread_info()->cpu;
+ return cpumask_test_cpu(cpu, &mmu_enabled_cpumask);
+ }
+
+ 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 773337e6d3b7..9d5759686b73 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 read_sysreg(SCTRL) & CR_M;
+}
diff --git a/lib/arm64/asm/processor.h b/lib/arm64/asm/processor.h
index 771b2d1e0c94..8e2037e1a43e 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/arm64/processor.c b/lib/arm64/processor.c
index 2a024e3f4e9d..ef558625e284 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;
+}
