On Fri, Jan 05, 2024 at 06:55:31PM -0800, Atish Patra wrote:
> On Wed, Dec 13, 2023 at 2:48 PM Charlie Jenkins <charlie@xxxxxxxxxxxx> wrote:
> >
> > Support new prctl with key PR_RISCV_SET_ICACHE_FLUSH_CTX to enable
> > optimization of cross modifying code. This prctl enables userspace code
> > to use icache flushing instructions such as fence.i with the guarantee
> > that the icache will continue to be clean after thread migration.
> >
>
> Do we need a CLEAR option as well ? I am wondering if there is a use case where
> an application wants the prctl for only certain duration but may
> invoke fence.i multiple times (syscall will still not be a good option
> for them.)
Having a clear option does seem like a good idea. I will send out a new
patch with a context option that can be similar to
PR_RISCV_CTX_SW_FENCEI_CLEAR.
- Charlie
>
> > Signed-off-by: Charlie Jenkins <charlie@xxxxxxxxxxxx>
> > ---
> > arch/riscv/include/asm/mmu.h | 2 ++
> > arch/riscv/include/asm/processor.h | 6 ++++++
> > arch/riscv/mm/cacheflush.c | 37 +++++++++++++++++++++++++++++++++++++
> > arch/riscv/mm/context.c | 8 +++++---
> > include/uapi/linux/prctl.h | 3 +++
> > kernel/sys.c | 6 ++++++
> > 6 files changed, 59 insertions(+), 3 deletions(-)
> >
> > diff --git a/arch/riscv/include/asm/mmu.h b/arch/riscv/include/asm/mmu.h
> > index 355504b37f8e..60be458e94da 100644
> > --- a/arch/riscv/include/asm/mmu.h
> > +++ b/arch/riscv/include/asm/mmu.h
> > @@ -19,6 +19,8 @@ typedef struct {
> > #ifdef CONFIG_SMP
> > /* A local icache flush is needed before user execution can resume. */
> > cpumask_t icache_stale_mask;
> > + /* Force local icache flush on all migrations. */
> > + bool force_icache_flush;
> > #endif
> > #ifdef CONFIG_BINFMT_ELF_FDPIC
> > unsigned long exec_fdpic_loadmap;
> > diff --git a/arch/riscv/include/asm/processor.h b/arch/riscv/include/asm/processor.h
> > index f19f861cda54..7eda6c75e0f2 100644
> > --- a/arch/riscv/include/asm/processor.h
> > +++ b/arch/riscv/include/asm/processor.h
> > @@ -84,6 +84,9 @@ struct thread_struct {
> > unsigned long vstate_ctrl;
> > struct __riscv_v_ext_state vstate;
> > unsigned long align_ctl;
> > +#ifdef CONFIG_SMP
> > + bool force_icache_flush;
> > +#endif
> > };
> >
> > /* Whitelist the fstate from the task_struct for hardened usercopy */
> > @@ -145,6 +148,9 @@ extern int set_unalign_ctl(struct task_struct *tsk, unsigned int val);
> > #define GET_UNALIGN_CTL(tsk, addr) get_unalign_ctl((tsk), (addr))
> > #define SET_UNALIGN_CTL(tsk, val) set_unalign_ctl((tsk), (val))
> >
> > +#define RISCV_SET_ICACHE_FLUSH_CTX(arg1, arg2) riscv_set_icache_flush_ctx(arg1, arg2)
> > +extern int riscv_set_icache_flush_ctx(unsigned long ctx, unsigned long per_thread);
> > +
> > #endif /* __ASSEMBLY__ */
> >
> > #endif /* _ASM_RISCV_PROCESSOR_H */
> > diff --git a/arch/riscv/mm/cacheflush.c b/arch/riscv/mm/cacheflush.c
> > index 55a34f2020a8..3b2bf8256a10 100644
> > --- a/arch/riscv/mm/cacheflush.c
> > +++ b/arch/riscv/mm/cacheflush.c
> > @@ -5,6 +5,7 @@
> >
> > #include <linux/acpi.h>
> > #include <linux/of.h>
> > +#include <linux/prctl.h>
> > #include <asm/acpi.h>
> > #include <asm/cacheflush.h>
> >
> > @@ -152,3 +153,39 @@ void __init riscv_init_cbo_blocksizes(void)
> > if (cboz_block_size)
> > riscv_cboz_block_size = cboz_block_size;
> > }
> > +
> > +/**
> > + * riscv_set_icache_flush_ctx() - Enable userspace to emit icache flushing instructions.
> > + * @ctx: Sets the type of context
> > + * - PR_RISCV_CTX_SW_FENCEI: Allow fence.i in userspace. Another fence.i will
> > + * emitted on thread/process migration.
> > + * @per_thread: When set to 0, will use the default behavior of setting the
> > + * icache flush context per process. When set to 1, will use a per thread
> > + * context.
> > + *
> > + * When in per-process context, there may be multiple threads using the same mm.
> > + * Therefore, the icache can never be assumed clean when. Multiple threads in
> > + * the process may modify instructions in the mm concurrently.
> > + *
> > + * In per-thread context, it can be assumed that all modifications to
> > + * instructions in memory will be performed by this thread. When the thread is
> > + * migrated the icache will be flushed.
> > + *
> > + */
> > +int riscv_set_icache_flush_ctx(unsigned long ctx, unsigned long per_thread)
> > +{
> > +#ifdef CONFIG_SMP
> > + switch (ctx) {
> > + case PR_RISCV_CTX_SW_FENCEI:
> > + if (per_thread)
> > + current->thread.force_icache_flush = true;
> > + else
> > + current->mm->context.force_icache_flush = true;
> > + break;
> > +
> > + default:
> > + break;
> > + }
> > +#endif
> > + return 0;
> > +}
> > diff --git a/arch/riscv/mm/context.c b/arch/riscv/mm/context.c
> > index 217fd4de6134..0146c61be0ab 100644
> > --- a/arch/riscv/mm/context.c
> > +++ b/arch/riscv/mm/context.c
> > @@ -297,12 +297,14 @@ static inline void set_mm(struct mm_struct *prev,
> > *
> > * The "cpu" argument must be the current local CPU number.
> > */
> > -static inline void flush_icache_deferred(struct mm_struct *mm, unsigned int cpu)
> > +static inline void flush_icache_deferred(struct mm_struct *mm, unsigned int cpu,
> > + struct task_struct *task)
> > {
> > #ifdef CONFIG_SMP
> > cpumask_t *mask = &mm->context.icache_stale_mask;
> >
> > - if (cpumask_test_cpu(cpu, mask)) {
> > + if (cpumask_test_cpu(cpu, mask) || mm->context.force_icache_flush ||
> > + (task && task->thread.force_icache_flush)) {
> > cpumask_clear_cpu(cpu, mask);
> > /*
> > * Ensure the remote hart's writes are visible to this hart.
> > @@ -332,5 +334,5 @@ void switch_mm(struct mm_struct *prev, struct mm_struct *next,
> >
> > set_mm(prev, next, cpu);
> >
> > - flush_icache_deferred(next, cpu);
> > + flush_icache_deferred(next, cpu, task);
> > }
> > diff --git a/include/uapi/linux/prctl.h b/include/uapi/linux/prctl.h
> > index 370ed14b1ae0..472801ea78cc 100644
> > --- a/include/uapi/linux/prctl.h
> > +++ b/include/uapi/linux/prctl.h
> > @@ -306,4 +306,7 @@ struct prctl_mm_map {
> > # define PR_RISCV_V_VSTATE_CTRL_NEXT_MASK 0xc
> > # define PR_RISCV_V_VSTATE_CTRL_MASK 0x1f
> >
> > +#define PR_RISCV_SET_ICACHE_FLUSH_CTX 71
> > +# define PR_RISCV_CTX_SW_FENCEI 0
> > +
> > #endif /* _LINUX_PRCTL_H */
> > diff --git a/kernel/sys.c b/kernel/sys.c
> > index 420d9cb9cc8e..e806a8a67c36 100644
> > --- a/kernel/sys.c
> > +++ b/kernel/sys.c
> > @@ -146,6 +146,9 @@
> > #ifndef RISCV_V_GET_CONTROL
> > # define RISCV_V_GET_CONTROL() (-EINVAL)
> > #endif
> > +#ifndef RISCV_SET_ICACHE_FLUSH_CTX
> > +# define RISCV_SET_ICACHE_FLUSH_CTX(a, b) (-EINVAL)
> > +#endif
> >
> > /*
> > * this is where the system-wide overflow UID and GID are defined, for
> > @@ -2739,6 +2742,9 @@ SYSCALL_DEFINE5(prctl, int, option, unsigned long, arg2, unsigned long, arg3,
> > case PR_RISCV_V_GET_CONTROL:
> > error = RISCV_V_GET_CONTROL();
> > break;
> > + case PR_RISCV_SET_ICACHE_FLUSH_CTX:
> > + error = RISCV_SET_ICACHE_FLUSH_CTX(arg2, arg3);
> > + break;
> > default:
> > error = -EINVAL;
> > break;
> >
> > --
> > 2.43.0
> >
> >
> > _______________________________________________
> > linux-riscv mailing list
> > linux-riscv@xxxxxxxxxxxxxxxxxxx
> > http://lists.infradead.org/mailman/listinfo/linux-riscv
>
>
>
> --
> Regards,
> Atish
