On Tue, Mar 23, 2021 at 11:40:37AM +0000, Alexandru Elisei wrote: > Hi Drew, > > On 3/23/21 11:24 AM, Andrew Jones wrote: > > 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. > > The diff looks good, and I agree that we can come back to #3 once we have a better > understanding of what needs to be done. Patch #1 is a nice fix for what I imagine > was a hard to find bug. Patch #4 also looks correct to me. Yes, please add my > Reviewed-by for the series. > > Thanks, > > Alex Thanks, applied 1, 2, and 4 to arm/queue https://gitlab.com/rhdrjones/kvm-unit-tests/-/commits/arm/queue Thanks, drew > > > > > 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; > > +} > > >
