On Sun, Feb 18, 2024 at 02:15:53AM +0100, Alejandro Colomar wrote: > 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. Sure thing. Thank you! > > 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.
