Messages in this thread Patch in this message |  | | Subject | [PATCH v10 14/14] powerpc: Use mm_context vas_windows counter to issue CP_ABORT | From | Haren Myneni <> | Date | Thu, 02 Apr 2020 00:20:24 -0700 |
| |
set_thread_uses_vas() sets used_vas flag for a process that opened VAS window and issue CP_ABORT during context switch for only that process. In multi-thread application, windows can be shared. For example Thread A can open a window and Thread B can run COPY/PASTE instructions to send NX request which may cause corruption or snooping or a covert channel. Also once this flag is set, continue to run CP_ABORT even the VAS window is closed.
So define vas-windows counter in process mm_context, increment this counter for each window open and decrement it for window close. If vas-windows is set, issue CP_ABORT during context switch. It means clear the foreign real address mapping only if the process / thread uses COPY/PASTE. Then disable it for that process if windows are not open.
Signed-off-by: Haren Myneni <haren@linux.ibm.com> Reported-by: Nicholas Piggin <npiggin@gmail.com> Suggested-by: Milton Miller <miltonm@us.ibm.com> Suggested-by: Nicholas Piggin <npiggin@gmail.com> --- arch/powerpc/include/asm/book3s/64/mmu.h | 3 +++ arch/powerpc/include/asm/mmu_context.h | 22 ++++++++++++++++++++++ arch/powerpc/include/asm/processor.h | 1 - arch/powerpc/kernel/process.c | 8 ++++++-- arch/powerpc/platforms/powernv/vas-window.c | 1 + 5 files changed, 32 insertions(+), 3 deletions(-)
diff --git a/arch/powerpc/include/asm/book3s/64/mmu.h b/arch/powerpc/include/asm/book3s/64/mmu.h index bb3deb7..f0a9ff6 100644 --- a/arch/powerpc/include/asm/book3s/64/mmu.h +++ b/arch/powerpc/include/asm/book3s/64/mmu.h @@ -116,6 +116,9 @@ struct patb_entry { /* Number of users of the external (Nest) MMU */ atomic_t copros; + /* Number of user space windows opened in process mm_context */ + atomic_t vas_windows; + struct hash_mm_context *hash_context; unsigned long vdso_base; diff --git a/arch/powerpc/include/asm/mmu_context.h b/arch/powerpc/include/asm/mmu_context.h index 360367c..7fd249498 100644 --- a/arch/powerpc/include/asm/mmu_context.h +++ b/arch/powerpc/include/asm/mmu_context.h @@ -185,11 +185,33 @@ static inline void mm_context_remove_copro(struct mm_struct *mm) dec_mm_active_cpus(mm); } } + +/* + * vas_windows counter shows number of open windows in the mm + * context. During context switch, use this counter to clear the + * foreign real address mapping (CP_ABORT) for the thread / process + * that intend to use COPY/PASTE. When a process closes all windows, + * disable CP_ABORT which is expensive to run. + */ +static inline void mm_context_add_vas_windows(struct mm_struct *mm) +{ + atomic_inc(&mm->context.vas_windows); +} + +static inline void mm_context_remove_vas_windows(struct mm_struct *mm) +{ + int c = atomic_dec_if_positive(&mm->context.vas_windows); + + /* Detect imbalance between add and remove */ + WARN_ON(c < 0); +} #else static inline void inc_mm_active_cpus(struct mm_struct *mm) { } static inline void dec_mm_active_cpus(struct mm_struct *mm) { } static inline void mm_context_add_copro(struct mm_struct *mm) { } static inline void mm_context_remove_copro(struct mm_struct *mm) { } +static inline void mm_context_add_vas_windows(struct mm_struct *mm) { } +static inline void mm_context_remove_vas_windows(struct mm_struct *mm) { } #endif diff --git a/arch/powerpc/include/asm/processor.h b/arch/powerpc/include/asm/processor.h index eedcbfb..bfa336f 100644 --- a/arch/powerpc/include/asm/processor.h +++ b/arch/powerpc/include/asm/processor.h @@ -272,7 +272,6 @@ struct thread_struct { unsigned mmcr0; unsigned used_ebb; - unsigned int used_vas; #endif }; diff --git a/arch/powerpc/kernel/process.c b/arch/powerpc/kernel/process.c index fad50db..a3ecaf9 100644 --- a/arch/powerpc/kernel/process.c +++ b/arch/powerpc/kernel/process.c @@ -1221,7 +1221,8 @@ struct task_struct *__switch_to(struct task_struct *prev, * mappings, we must issue a cp_abort to clear any state and * prevent snooping, corruption or a covert channel. */ - if (current->thread.used_vas) + if (current->mm && + atomic_read(¤t->mm->context.vas_windows)) asm volatile(PPC_CP_ABORT); } #endif /* CONFIG_PPC_BOOK3S_64 */ @@ -1466,7 +1467,10 @@ int set_thread_uses_vas(void) if (!cpu_has_feature(CPU_FTR_ARCH_300)) return -EINVAL; - current->thread.used_vas = 1; + if (!current->mm) + return -EINVAL; + + mm_context_add_vas_windows(current->mm); /* * Even a process that has no foreign real address mapping can use diff --git a/arch/powerpc/platforms/powernv/vas-window.c b/arch/powerpc/platforms/powernv/vas-window.c index 3ffad5a..33dfbbf 100644 --- a/arch/powerpc/platforms/powernv/vas-window.c +++ b/arch/powerpc/platforms/powernv/vas-window.c @@ -1333,6 +1333,7 @@ int vas_win_close(struct vas_window *window) put_pid(window->pid); if (window->mm) { mm_context_remove_copro(window->mm); + mm_context_remove_vas_windows(window->mm); mmdrop(window->mm); } } -- 1.8.3.1
|  |