Hi Charlie, On Mon, Feb 12, 2024 at 09:19:21PM -0500, Charlie Jenkins wrote: > I have proposed and documented the PR_RISCV_SET_ICACHE_FLUSH_CTX flag > for prctl(2) to LKML. It has been reviewed and is expected to land > during the Linux version 6.9 merge window. This adds the relevant > documentation from that patch. > > Signed-off-by: Charlie Jenkins <charlie@xxxxxxxxxxxx> > --- > I have proposed and documented the PR_RISCV_SET_ICACHE_FLUSH_CTX > flag for prctl(2) to LKML. It has been reviewed and is expected to land > during the Linux version 6.9 merge window. Can you please ping when that happens? The below LGTM. Have a lovely night! Alex > --- > Changes in v2: > - Update formatting (Alejandro) > - Link to v1: https://lore.kernel.org/r/20240124-fencei_prctl-v1-1-0bddafcef331@xxxxxxxxxxxx > --- > man2/prctl.2 | 59 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ > 1 file changed, 59 insertions(+) > > diff --git a/man2/prctl.2 b/man2/prctl.2 > index f1604a7cb..32ce8474f 100644 > --- a/man2/prctl.2 > +++ b/man2/prctl.2 > @@ -1147,6 +1147,65 @@ For further information, see the kernel source file > (or > .I Documentation/security/Yama.txt > before Linux 4.13). > +.\" prctl PR_RISCV_SET_ICACHE_FLUSH_CTX > +.TP > +.BR PR_RISCV_SET_ICACHE_FLUSH_CTX " (since Linux 6.9, RISC-V only)" > +Enable/disable icache flushing instructions in userspace. > +The context and the scope can be provided using > +.I arg2 > +and > +.I arg3 > +respectively. > +When scope is set to > +.B PR_RISCV_SCOPE_PER_PROCESS > +all threads in the process are permitted to emit icache flushing instructions. > +Whenever any thread in the process is migrated, the corresponding hart's > +icache will be guaranteed to be consistent with instruction storage. > +This does not enforce any guarantees outside of migration. > +If a thread modifies an instruction that another thread may attempt to > +execute, the other thread must still emit an icache flushing instruction > +before attempting to execute the potentially modified instruction. > +This must be performed by the user-space program. > +.IP > +In per-thread context (eg. scope is set to > +.BR PR_RISCV_SCOPE_PER_THREAD ) > +only the thread calling this function is permitted to emit icache flushing > +instructions. > +When the thread is migrated, the corresponding hart's icache will be > +guaranteed to be consistent with instruction storage. > +.IP > +On kernels configured without SMP, this function is a nop as migrations across > +harts will not occur. > +.IP > +The following values for > +.I arg2 > +can be specified: > +.RS > +.TP > +.BR PR_RISCV_CTX_SW_FENCEI_ON " (since Linux 6.9)" > +Allow fence.i in user space. > +.TP > +.BR PR_RISCV_CTX_SW_FENCEI_OFF " (since Linux 6.9)" > +Disallow fence.i in user space. > +All threads in a process will be affected when scope is set to > +.BR PR_RISCV_SCOPE_PER_PROCESS . > +Therefore, caution must be taken; use this flag only when you can guarantee > +that no thread in the process will emit fence.i from this point onward. > +.RE > +.IP > +The following values for > +.I arg3 > +can be specified: > +.RS > +.TP > +.BR PR_RISCV_SCOPE_PER_PROCESS " (since Linux 6.9)" > +Ensure the icache of any thread in this process is coherent with instruction > +storage upon migration. > +.TP > +.BR PR_RISCV_SCOPE_PER_THREAD " (since Linux 6.9)" > +Ensure the icache of the current thread is coherent with instruction storage > +upon migration. > +.RE > .\" prctl PR_SET_SECCOMP > .TP > .BR PR_SET_SECCOMP " (since Linux 2.6.23)" > > --- > base-commit: a81e893f2b9316869e6098c3a079c30a48158092 > change-id: 20240124-fencei_prctl-c24da2643379 > > Best regards, > -- > Charlie Jenkins <charlie@xxxxxxxxxxxx> > -- <https://www.alejandro-colomar.es/> Looking for a remote C programming job at the moment.
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