kernel.git/arch/s390/kernel/smp.c, branch linux-5.4.y

treewide: Remove uninitialized_var() usage

2023-06-09T08:29:01Z

commit 3f649ab728cda8038259d8f14492fe400fbab911 upstream. Using uninitialized_var() is dangerous as it papers over real bugs[1] (or can in the future), and suppresses unrelated compiler warnings (e.g. "unused variable"). If the compiler thinks it is uninitialized, either simply initialize the variable or make compiler changes. In preparation for removing[2] the[3] macro[4], remove all remaining needless uses with the following script: git grep '\buninitialized_var\b' | cut -d: -f1 | sort -u | \ xargs perl -pi -e \ 's/\buninitialized_var$([^$]+)\)/\1/g; s:\s*/\* (GCC be quiet|to make compiler happy) \*/$::g;' drivers/video/fbdev/riva/riva_hw.c was manually tweaked to avoid pathological white-space. No outstanding warnings were found building allmodconfig with GCC 9.3.0 for x86_64, i386, arm64, arm, powerpc, powerpc64le, s390x, mips, sparc64, alpha, and m68k. [1] https://lore.kernel.org/lkml/20200603174714.192027-1-glider@google.com/ [2] https://lore.kernel.org/lkml/CA+55aFw+Vbj0i=1TGqCR5vQkCzWJ0QxK6CernOU6eedsudAixw@mail.gmail.com/ [3] https://lore.kernel.org/lkml/CA+55aFwgbgqhbp1fkxvRKEpzyR5J8n1vKT1VZdz9knmPuXhOeg@mail.gmail.com/ [4] https://lore.kernel.org/lkml/CA+55aFz2500WfbKXAx8s67wrm9=yVJu65TpLgN_ybYNv0VEOKA@mail.gmail.com/ Reviewed-by: Leon Romanovsky # drivers/infiniband and mlx4/mlx5 Acked-by: Jason Gunthorpe # IB Acked-by: Kalle Valo # wireless drivers Reviewed-by: Chao Yu # erofs Signed-off-by: Kees Cook Signed-off-by: Greg Kroah-Hartman

s390/smp: __smp_rescan_cpus() - move cpumask away from stack

2021-03-17T16:03:45Z

[ Upstream commit 62c8dca9e194326802b43c60763f856d782b225c ] Avoid a potentially large stack frame and overflow by making "cpumask_t avail" a static variable. There is no concurrent access due to the existing locking. Signed-off-by: Heiko Carstens Signed-off-by: Vasily Gorbik Signed-off-by: Sasha Levin

s390/smp: perform initial CPU reset also for SMT siblings

2020-12-30T10:51:34Z

commit b5e438ebd7e808d1d2435159ac4742e01a94b8da upstream. Not resetting the SMT siblings might leave them in unpredictable state. One of the observed problems was that the CPU timer wasn't reset and therefore large system time values where accounted during CPU bringup. Cc: # 4.0 Fixes: 10ad34bc76dfb ("s390: add SMT support") Reviewed-by: Heiko Carstens Signed-off-by: Sven Schnelle Signed-off-by: Heiko Carstens Signed-off-by: Greg Kroah-Hartman

s390/smp: move rcu_cpu_starting() earlier

2020-11-18T18:20:24Z

[ Upstream commit de5d9dae150ca1c1b5c7676711a9ca139d1a8dec ] The call to rcu_cpu_starting() in smp_init_secondary() is not early enough in the CPU-hotplug onlining process, which results in lockdep splats as follows: WARNING: suspicious RCU usage ----------------------------- kernel/locking/lockdep.c:3497 RCU-list traversed in non-reader section!! other info that might help us debug this: RCU used illegally from offline CPU! rcu_scheduler_active = 1, debug_locks = 1 no locks held by swapper/1/0. Call Trace: show_stack+0x158/0x1f0 dump_stack+0x1f2/0x238 __lock_acquire+0x2640/0x4dd0 lock_acquire+0x3a8/0xd08 _raw_spin_lock_irqsave+0xc0/0xf0 clockevents_register_device+0xa8/0x528 init_cpu_timer+0x33e/0x468 smp_init_secondary+0x11a/0x328 smp_start_secondary+0x82/0x88 This is avoided by moving the call to rcu_cpu_starting up near the beginning of the smp_init_secondary() function. Note that the raw_smp_processor_id() is required in order to avoid calling into lockdep before RCU has declared the CPU to be watched for readers. Link: https://lore.kernel.org/lkml/160223032121.7002.1269740091547117869.tip-bot2@tip-bot2/ Signed-off-by: Qian Cai Acked-by: Paul E. McKenney Signed-off-by: Heiko Carstens Signed-off-by: Sasha Levin

s390: avoid misusing CALL_ON_STACK for task stack setup

2020-10-01T11:17:22Z

[ Upstream commit 7bcaad1f9fac889f5fcd1a383acf7e00d006da41 ] CALL_ON_STACK is intended to be used for temporary stack switching with potential return to the caller. When CALL_ON_STACK is misused to switch from nodat stack to task stack back_chain information would later lead stack unwinder from task stack into (per cpu) nodat stack which is reused for other purposes. This would yield confusing unwinding result or errors. To avoid that introduce CALL_ON_STACK_NORETURN to be used instead. It makes sure that back_chain is zeroed and unwinder finishes gracefully ending up at task pt_regs. Reviewed-by: Heiko Carstens Signed-off-by: Vasily Gorbik Signed-off-by: Sasha Levin

s390/ftrace: fix potential crashes when switching tracers

2020-05-02T06:48:44Z

commit 8ebf6da9db1b2a20bb86cc1bee2552e894d03308 upstream. Switching tracers include instruction patching. To prevent that a instruction is patched while it's read the instruction patching is done in stop_machine 'context'. This also means that any function called during stop_machine must not be traced. Thus add 'notrace' to all functions called within stop_machine. Fixes: 1ec2772e0c3c ("s390/diag: add a statistic for diagnose calls") Fixes: 38f2c691a4b3 ("s390: improve wait logic of stop_machine") Fixes: 4ecf0a43e729 ("processor: get rid of cpu_relax_yield") Signed-off-by: Philipp Rudo Signed-off-by: Vasily Gorbik Signed-off-by: Greg Kroah-Hartman

s390: prevent leaking kernel address in BEAR

2020-04-13T08:48:06Z

commit 0b38b5e1d0e2f361e418e05c179db05bb688bbd6 upstream. When userspace executes a syscall or gets interrupted, BEAR contains a kernel address when returning to userspace. This make it pretty easy to figure out where the kernel is mapped even with KASLR enabled. To fix this, add lpswe to lowcore and always execute it there, so userspace sees only the lowcore address of lpswe. For this we have to extend both critical_cleanup and the SWITCH_ASYNC macro to also check for lpswe addresses in lowcore. Fixes: b2d24b97b2a9 ("s390/kernel: add support for kernel address space layout randomization (KASLR)") Cc: # v5.2+ Reviewed-by: Gerald Schaefer Signed-off-by: Sven Schnelle Signed-off-by: Vasily Gorbik Signed-off-by: Greg Kroah-Hartman

s390/smp: fix physical to logical CPU map for SMT

2020-01-09T09:20:06Z

[ Upstream commit 72a81ad9d6d62dcb79f7e8ad66ffd1c768b72026 ] If an SMT capable system is not IPL'ed from the first CPU the setup of the physical to logical CPU mapping is broken: the IPL core gets CPU number 0, but then the next core gets CPU number 1. Correct would be that all SMT threads of CPU 0 get the subsequent logical CPU numbers. This is important since a lot of code (like e.g. the CPU topology code) assumes that CPU maps are setup like this. If the mapping is broken the system will not IPL due to broken topology masks: [ 1.716341] BUG: arch topology broken [ 1.716342] the SMT domain not a subset of the MC domain [ 1.716343] BUG: arch topology broken [ 1.716344] the MC domain not a subset of the BOOK domain This scenario can usually not happen since LPARs are always IPL'ed from CPU 0 and also re-IPL is intiated from CPU 0. However older kernels did initiate re-IPL on an arbitrary CPU. If therefore a re-IPL from an old kernel into a new kernel is initiated this may lead to crash. Fix this by setting up the physical to logical CPU mapping correctly. Signed-off-by: Heiko Carstens Signed-off-by: Vasily Gorbik Signed-off-by: Sasha Levin

s390/smp,vdso: fix ASCE handling

2019-12-17T18:56:50Z

commit a2308c11ecbc3471ebb7435ee8075815b1502ef0 upstream. When a secondary CPU is brought up it must initialize its control registers. CPU A which triggers that a secondary CPU B is brought up stores its control register contents into the lowcore of new CPU B, which then loads these values on startup. This is problematic in various ways: the control register which contains the home space ASCE will correctly contain the kernel ASCE; however control registers for primary and secondary ASCEs are initialized with whatever values were present in CPU A. Typically: - the primary ASCE will contain the user process ASCE of the process that triggered onlining of CPU B. - the secondary ASCE will contain the percpu VDSO ASCE of CPU A. Due to lazy ASCE handling we may also end up with other combinations. When then CPU B switches to a different process (!= idle) it will fixup the primary ASCE. However the problem is that the (wrong) ASCE from CPU A was loaded into control register 1: as soon as an ASCE is attached (aka loaded) a CPU is free to generate TLB entries using that address space. Even though it is very unlikey that CPU B will actually generate such entries, this could result in TLB entries of the address space of the process that ran on CPU A. These entries shouldn't exist at all and could cause problems later on. Furthermore the secondary ASCE of CPU B will not be updated correctly. This means that processes may see wrong results or even crash if they access VDSO data on CPU B. The correct VDSO ASCE will eventually be loaded on return to user space as soon as the kernel executed a call to strnlen_user or an atomic futex operation on CPU B. Fix both issues by intializing the to be loaded control register contents with the correct ASCEs and also enforce (re-)loading of the ASCEs upon first context switch and return to user space. Fixes: 0aaba41b58bc ("s390: remove all code using the access register mode") Cc: stable@vger.kernel.org # v4.15+ Signed-off-by: Heiko Carstens Signed-off-by: Vasily Gorbik Signed-off-by: Greg Kroah-Hartman

s390: improve wait logic of stop_machine

2019-06-15T10:25:52Z

The stop_machine loop to advance the state machine and to wait for all affected CPUs to check-in calls cpu_relax_yield in a tight loop until the last missing CPUs acknowledged the state transition. On a virtual system where not all logical CPUs are backed by real CPUs all the time it can take a while for all CPUs to check-in. With the current definition of cpu_relax_yield a diagnose 0x44 is done which tells the hypervisor to schedule *some* other CPU. That can be any CPU and not necessarily one of the CPUs that need to run in order to advance the state machine. This can lead to a pretty bad diagnose 0x44 storm until the last missing CPU finally checked-in. Replace the undirected cpu_relax_yield based on diagnose 0x44 with a directed yield. Each CPU in the wait loop will pick up the next CPU in the cpumask of stop_machine. The diagnose 0x9c is used to tell the hypervisor to run this next CPU instead of the current one. If there is only a limited number of real CPUs backing the virtual CPUs we end up with the real CPUs passed around in a round-robin fashion. [heiko.carstens@de.ibm.com]: Use cpumask_next_wrap as suggested by Peter Zijlstra. Signed-off-by: Martin Schwidefsky Acked-by: Peter Zijlstra (Intel) Acked-by: Thomas Gleixner Signed-off-by: Heiko Carstens