Any comments for this revision? Hopefully these revisions address 32-bit and embedded systems appropriately.
Thanks, Rohan > On 24 Aug 2022, at 12:05 pm, Rohan McLure <rmcl...@linux.ibm.com> wrote: > > V3 available here: > > Link: > https://lore.kernel.org/all/4c3a8815-67ff-41eb-a703-981920ca1...@linux.ibm.com/T/ > > Implement a syscall wrapper, causing arguments to handlers to be passed > via a struct pt_regs on the stack. The syscall wrapper is implemented > for all platforms other than the Cell processor, from which SPUs expect > the ability to directly call syscall handler symbols with the regular > in-register calling convention. > > Adopting syscall wrappers requires redefinition of architecture-specific > syscalls and compatibility syscalls to use the SYSCALL_DEFINE and > COMPAT_SYSCALL_DEFINE macros, as well as removal of direct-references to > the emitted syscall-handler symbols from within the kernel. This work > lead to the following modernisations of powerpc's syscall handlers: > > - Replace syscall 82 semantics with sys_old_select and remove > ppc_select handler, which features direct call to both sys_old_select > and sys_select. > - Use a generic fallocate compatibility syscall > > Replace asm implementation of syscall table with C implementation for > more compile-time checks. > > Many compatibility syscalls are candidates to be removed in favour of > generically defined handlers, but exhibit different parameter orderings > and numberings due to 32-bit ABI support for 64-bit parameters. The > parameter reorderings are however consistent with arm. A future patch > series will serve to modernise syscalls by providing generic > implementations featuring these reorderings. > > The design of this syscall is very similar to the s390, x86 and arm64 > implementations. See also Commit 4378a7d4be30 (arm64: implement syscall > wrappers). > The motivation for this change is that it allows for the clearing of > register state when entering the kernel via through interrupt handlers > on 64-bit servers. This serves to reduce the influence of values in > registers carried over from the interrupted process, e.g. syscall > parameters from user space, or user state at the site of a pagefault. > All values in registers are saved and zeroized at the entry to an > interrupt handler and restored afterward. While this may sound like a > heavy-weight mitigation, many gprs are already saved and restored on > handling of an interrupt, and the mmap_bench benchmark on Power 9 guest, > repeatedly invoking the pagefault handler suggests at most ~0.8% > regression in performance. Realistic workloads are not constantly > producing interrupts, and so this does not indicate realistic slowdown. > > Using wrapped syscalls yields to a performance improvement of ~5.6% on > the null_syscall benchmark on pseries guests, by removing the need for > system_call_exception to allocate its own stack frame. This amortises > the additional costs of saving and restoring non-volatile registers > (register clearing is cheap on super scalar platforms), and so the > final mitigation actually yields a net performance improvement of ~0.6% > on the null_syscall benchmark. > > Patch Changelog: > > - Fix instances where NULLIFY_GPRS were still present > - Minimise unrecoverable windows in entry_32.S between SRR0/1 restores > and RFI > - Remove all references to syscall symbols prior to introducing syscall > wrapper. > - Remove unnecessary duplication of syscall handlers with sys_... and > powerpc_sys_... symbols. > - Clear non-volatile registers on Book3E systems, as some of these > systems feature hardware speculation, and we already unconditionally > restore NVGPRS. > > Rohan McLure (20): > powerpc: Remove asmlinkage from syscall handler definitions > powerpc: Use generic fallocate compatibility syscall > powerpc/32: Remove powerpc select specialisation > powerpc: Provide do_ppc64_personality helper > powerpc: Remove direct call to personality syscall handler > powerpc: Remove direct call to mmap2 syscall handlers > powerpc: Adopt SYSCALL_DEFINE for arch-specific syscall handlers > powerpc: Include all arch-specific syscall prototypes > powerpc: Enable compile-time check for syscall handlers > powerpc: Use common syscall handler type > powerpc: Add ZEROIZE_GPRS macros for register clears > Revert "powerpc/syscall: Save r3 in regs->orig_r3" > powerpc: Provide syscall wrapper > powerpc/64s: Clear/restore caller gprs in syscall interrupt/return > powerpc/64s: Use {ZEROIZE,SAVE,REST}_GPRS macros in sc, scv 0 handlers > powerpc/32: Clarify interrupt restores with REST_GPR macro in > entry_32.S > powerpc/64e: Clarify register saves and clears with > {SAVE,ZEROIZE}_GPRS > powerpc/64s: Fix comment on interrupt handler prologue > powerpc/64s: Clear gprs on interrupt routine entry in Book3S > powerpc/64e: Clear gprs on interrupt routine entry > > arch/powerpc/Kconfig | 1 + > arch/powerpc/include/asm/compat.h | 5 + > arch/powerpc/include/asm/interrupt.h | 3 +- > arch/powerpc/include/asm/ppc_asm.h | 22 +++ > arch/powerpc/include/asm/syscall.h | 11 +- > arch/powerpc/include/asm/syscall_wrapper.h | 84 +++++++++++ > arch/powerpc/include/asm/syscalls.h | 128 +++++++++++++---- > .../ppc32.h => include/asm/syscalls_32.h} | 0 > arch/powerpc/include/asm/unistd.h | 1 + > arch/powerpc/kernel/entry_32.S | 40 +++--- > arch/powerpc/kernel/exceptions-64e.S | 31 ++-- > arch/powerpc/kernel/exceptions-64s.S | 25 ++-- > arch/powerpc/kernel/interrupt_64.S | 92 +++++------- > arch/powerpc/kernel/signal_32.c | 2 +- > arch/powerpc/kernel/sys_ppc32.c | 54 ++++--- > arch/powerpc/kernel/syscall.c | 32 ++--- > arch/powerpc/kernel/syscalls.c | 51 ++++--- > arch/powerpc/kernel/syscalls/syscall.tbl | 24 ++-- > arch/powerpc/kernel/{systbl.S => systbl.c} | 29 ++-- > arch/powerpc/kernel/vdso.c | 6 +- > arch/powerpc/perf/callchain_32.c | 2 +- > arch/powerpc/platforms/cell/spu_callbacks.c | 6 +- > .../arch/powerpc/entry/syscalls/syscall.tbl | 24 ++-- > 23 files changed, 415 insertions(+), 258 deletions(-) > create mode 100644 arch/powerpc/include/asm/syscall_wrapper.h > rename arch/powerpc/{kernel/ppc32.h => include/asm/syscalls_32.h} (100%) > rename arch/powerpc/kernel/{systbl.S => systbl.c} (55%) > > -- > 2.34.1 >
