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Mon, 12 Sep 2022 00:55:52 GMT Received: from d06av23.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 86D65A404D; Mon, 12 Sep 2022 00:55:52 +0000 (GMT) Received: from d06av23.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id DD217A4040; Mon, 12 Sep 2022 00:55:51 +0000 (GMT) Received: from ozlabs.au.ibm.com (unknown [9.192.253.14]) by d06av23.portsmouth.uk.ibm.com (Postfix) with ESMTP; Mon, 12 Sep 2022 00:55:51 +0000 (GMT) Received: from smtpclient.apple (haven.au.ibm.com [9.192.254.114]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ozlabs.au.ibm.com (Postfix) with ESMTPSA id 79921600E5; Mon, 12 Sep 2022 10:55:42 +1000 (AEST) Content-Type: text/plain; charset=us-ascii Subject: Re: [PATCH v4 00/20] powerpc: Syscall wrapper and register clearing From: Rohan McLure In-Reply-To: <20220824020548.62625-1-rmclure@linux.ibm.com> Date: Mon, 12 Sep 2022 10:55:42 +1000 Message-Id: <0417F3C5-189E-4E3A-B4A9-9B3C597CC93A@linux.ibm.com> References: <20220824020548.62625-1-rmclure@linux.ibm.com> To: linuxppc-dev X-Mailer: Apple Mail (2.3696.120.41.1.1) X-TM-AS-GCONF: 00 X-Proofpoint-ORIG-GUID: vruJgaE9TB0-tIh8X3sZPtPV5-CtWT3h X-Proofpoint-GUID: _lO9lNEf77IrLmbSaLHFWCPApkNy7lDF Content-Transfer-Encoding: quoted-printable X-Proofpoint-UnRewURL: 0 URL was un-rewritten MIME-Version: 1.0 X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.205,Aquarius:18.0.895,Hydra:6.0.528,FMLib:17.11.122.1 definitions=2022-09-11_14,2022-09-09_01,2022-06-22_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 impostorscore=0 phishscore=0 clxscore=1011 lowpriorityscore=0 mlxlogscore=723 mlxscore=0 bulkscore=0 suspectscore=0 adultscore=0 priorityscore=1501 spamscore=0 malwarescore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2207270000 definitions=main-2209120000 X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Nicholas Piggin , Andrew Donnellan Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" Any comments for this revision? Hopefully these revisions address 32-bit an= d embedded systems appropriately. Thanks, Rohan > On 24 Aug 2022, at 12:05 pm, Rohan McLure wrote: >=20 > V3 available here: >=20 > Link: https://lore.kernel.org/all/4C3A8815-67FF-41EB-A703-981920CA1201@li= nux.ibm.com/T/ >=20 > 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. >=20 > 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: >=20 > - 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 >=20 > Replace asm implementation of syscall table with C implementation for > more compile-time checks. >=20 > 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. >=20 > The design of this syscall is very similar to the s390, x86 and arm64 > implementations. See also Commit 4378a7d4be30 (arm64: implement syscall w= rappers). > 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. >=20 > 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. >=20 > Patch Changelog: >=20 > - 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. >=20 > 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 >=20 > 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 =3D> 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 =3D> 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 =3D> include/asm/syscalls_32.h} (100%) > rename arch/powerpc/kernel/{systbl.S =3D> systbl.c} (55%) >=20 > --=20 > 2.34.1 >=20