diff options
author | Michael Ellerman <mpe@ellerman.id.au> | 2020-07-23 17:43:44 +1000 |
---|---|---|
committer | Michael Ellerman <mpe@ellerman.id.au> | 2020-07-23 17:43:44 +1000 |
commit | 335aca5f65f1a39670944930131da5f2276f888f (patch) | |
tree | c8f41223681fc064f558083a2d46f712e43d8b66 /arch/powerpc/include/asm/asm-prototypes.h | |
parent | selftests/powerpc: Add test of memcmp at end of page (diff) | |
parent | powerpc/64s: system call support for scv/rfscv instructions (diff) | |
download | linux-dev-335aca5f65f1a39670944930131da5f2276f888f.tar.xz linux-dev-335aca5f65f1a39670944930131da5f2276f888f.zip |
Merge branch 'scv' support into next
From Nick's cover letter:
Linux powerpc new system call instruction and ABI
System Call Vectored (scv) ABI
==============================
The scv instruction is introduced with POWER9 / ISA3, it comes with an
rfscv counter-part. The benefit of these instructions is
performance (trading slower SRR0/1 with faster LR/CTR registers, and
entering the kernel with MSR[EE] and MSR[RI] left enabled, which can
reduce MSR updates. The scv instruction has 128 levels (not enough to
cover the Linux system call space).
Assignment and advertisement
----------------------------
The proposal is to assign scv levels conservatively, and advertise
them with HWCAP feature bits as we add support for more.
Linux has not enabled FSCR[SCV] yet, so executing the scv instruction
will cause the kernel to log a "SCV facility unavilable" message, and
deliver a SIGILL with ILL_ILLOPC to the process. Linux has defined a
HWCAP2 bit PPC_FEATURE2_SCV for SCV support, but does not set it.
This change allocates the zero level ('scv 0'), advertised with
PPC_FEATURE2_SCV, which will be used to provide normal Linux system
calls (equivalent to 'sc').
Attempting to execute scv with other levels will cause a SIGILL to be
delivered the same as before, but will not log a "SCV facility
unavailable" message (because the processor facility is enabled).
Calling convention
------------------
The proposal is for scv 0 to provide the standard Linux system call
ABI with the following differences from sc convention[1]:
- LR is to be volatile across scv calls. This is necessary because the
scv instruction clobbers LR. From previous discussion, this should
be possible to deal with in GCC clobbers and CFI.
- cr1 and cr5-cr7 are volatile. This matches the C ABI and would allow
the kernel system call exit to avoid restoring the volatile cr
registers (although we probably still would anyway to avoid
information leaks).
- Error handling: The consensus among kernel, glibc, and musl is to
move to using negative return values in r3 rather than CR0[SO]=1 to
indicate error, which matches most other architectures, and is
closer to a function call.
Notes
-----
- r0,r4-r8 are documented as volatile in the ABI, but the kernel patch
as submitted currently preserves them. This is to leave room for
deciding which way to go with these. Some small benefit was found by
preserving them[1] but I'm not convinced it's worth deviating from
the C function call ABI just for this. Release code should follow
the ABI.
Previous discussions:
https://lists.ozlabs.org/pipermail/linuxppc-dev/2020-April/208691.html
https://lists.ozlabs.org/pipermail/linuxppc-dev/2020-April/209268.html
[1] https://github.com/torvalds/linux/blob/master/Documentation/powerpc/syscall64-abi.rst
[2] https://lists.ozlabs.org/pipermail/linuxppc-dev/2020-April/209263.html
Diffstat (limited to 'arch/powerpc/include/asm/asm-prototypes.h')
-rw-r--r-- | arch/powerpc/include/asm/asm-prototypes.h | 2 |
1 files changed, 1 insertions, 1 deletions
diff --git a/arch/powerpc/include/asm/asm-prototypes.h b/arch/powerpc/include/asm/asm-prototypes.h index fa9057360e88..de14b1a34d56 100644 --- a/arch/powerpc/include/asm/asm-prototypes.h +++ b/arch/powerpc/include/asm/asm-prototypes.h @@ -98,7 +98,7 @@ unsigned long __init early_init(unsigned long dt_ptr); void __init machine_init(u64 dt_ptr); #endif long system_call_exception(long r3, long r4, long r5, long r6, long r7, long r8, unsigned long r0, struct pt_regs *regs); -notrace unsigned long syscall_exit_prepare(unsigned long r3, struct pt_regs *regs); +notrace unsigned long syscall_exit_prepare(unsigned long r3, struct pt_regs *regs, long scv); notrace unsigned long interrupt_exit_user_prepare(struct pt_regs *regs, unsigned long msr); notrace unsigned long interrupt_exit_kernel_prepare(struct pt_regs *regs, unsigned long msr); |