kernel/linux.git/arch/arm/vfp, branch v6.3.2

ARM: 9293/1: vfp: Pass successful return address via register R3

2023-05-11T14:16:56+00:00

[ Upstream commit 3a2bdad0b46649cc73fb3b3f9e2b91ef97a7fa63 ] In preparation for reimplementing the do_vfp()->vfp_support_entry() handover in C code, switch to using R3 to pass the 'success' return address, rather than R9, as it cannot be used for parameter passing. Signed-off-by: Ard Biesheuvel Reviewed-by: Linus Walleij Tested-by: Guenter Roeck Signed-off-by: Russell King (Oracle) Stable-dep-of: c76c6c4ecbec ("ARM: 9294/2: vfp: Fix broken softirq handling with instrumentation enabled") Signed-off-by: Sasha Levin

ARM: 9292/1: vfp: Pass thread_info pointer to vfp_support_entry

2023-05-11T14:16:56+00:00

[ Upstream commit dae904d96ad6a5fa79bd9d99a3decf93685d398b ] Instead of dereferencing thread_info in do_vfp, pass the thread_info pointer to vfp_support_entry via R1. That way, we only use a single caller save register, which makes it easier to convert do_vfp to C code in a subsequent patch. Note that, unlike the CPU number, which can change due to preemption, passing the thread_info pointer can safely be done with preemption enabled. Signed-off-by: Ard Biesheuvel Reviewed-by: Linus Walleij Tested-by: Guenter Roeck Signed-off-by: Russell King (Oracle) Stable-dep-of: c76c6c4ecbec ("ARM: 9294/2: vfp: Fix broken softirq handling with instrumentation enabled") Signed-off-by: Sasha Levin

ARM: 9283/1: permit non-nested kernel mode NEON in softirq context

2023-01-11T16:21:21+00:00

We currently only permit kernel mode NEON in process context, to avoid the need to preserve/restore the NEON register file when taking an exception while running in the kernel. Like we did on arm64, we can relax this restriction substantially, by permitting kernel mode NEON from softirq context, while ensuring that softirq processing is disabled when the NEON is being used in task context. This guarantees that only NEON context belonging to user space needs to be preserved and restored, which is already taken care of. This is especially relevant for network encryption, where incoming frames are typically handled in softirq context, and deferring software decryption to a kernel thread or falling back to C code are both undesirable from a performance PoV. Tested-by: Martin Willi Reviewed-by: Linus Walleij Signed-off-by: Ard Biesheuvel Signed-off-by: Russell King (Oracle)

ARM: 9282/1: vfp: Manipulate task VFP state with softirqs disabled

2023-01-11T16:21:20+00:00

In a subsequent patch, we will relax the kernel mode NEON policy, and permit kernel mode NEON to be used not only from task context, as is permitted today, but also from softirq context. Given that softirqs may trigger over the back of any IRQ unless they are explicitly disabled, we need to address the resulting races in the VFP state handling, by disabling softirq processing in two distinct but related cases: - kernel mode NEON will leave the FPU disabled after it completes, so any kernel code sequence that enables the FPU and subsequently accesses its registers needs to disable softirqs until it completes; - kernel_neon_begin() will preserve the userland VFP state in memory, and if it interrupts the ordinary VFP state preserve sequence, the latter will resume execution with the VFP registers corrupted, and happily continue saving them to memory. Given that disabling softirqs also disables preemption, we can replace the existing preempt_disable/enable occurrences in the VFP state handling asm code with new macros that dis/enable softirqs instead. In the VFP state handling C code, add local_bh_disable/enable() calls in those places where the VFP state is preserved. One thing to keep in mind is that, once we allow NEON use in softirq context, the result of any such interruption is that the FPEXC_EN bit in the FPEXC register will be cleared, and vfp_current_hw_state[cpu] will be NULL. This means that any sequence that [conditionally] clears FPEXC_EN and/or sets vfp_current_hw_state[cpu] to NULL does not need to run with softirqs disabled, as the result will be the same. Furthermore, the handling of THREAD_NOTIFY_SWITCH is guaranteed to run with IRQs disabled, and so it does not need protection from softirq interruptions either. Tested-by: Martin Willi Reviewed-by: Linus Walleij Signed-off-by: Ard Biesheuvel Signed-off-by: Russell King (Oracle)

ARM: 9272/1: vfp: Add hwcap for FEAT_AA32I8MM

2022-11-28T11:57:34+00:00

Int8 matrix multiplication (FEAT_AA32I8MM) is a feature present in AArch32 state for Armv8 and is represented by ISAR6.I8MM identification register. This feature denotes the presence of VSMMLA, VSUDOT, VUMMLA, VUSMMLA and VUSDOT instructions and hence adding a hwcap will enable the userspace to check it before trying to use those instructions. Reviewed-by: Linus Walleij Signed-off-by: Amit Daniel Kachhap Signed-off-by: Russell King (Oracle)

ARM: 9271/1: vfp: Add hwcap for FEAT_AA32BF16

2022-11-28T11:57:33+00:00

Advanced SIMD BFloat16 (FEAT_AA32BF16) is a feature present in AArch32 state for Armv8 and is represented by ISAR6.BF16 identification register. This feature denotes the presence of VCVT, VCVTB, VCVTT, VDOT, VFMAB, VFMAT and VMMLA instructions and hence adding a hwcap will enable the userspace to check it before trying to use those instructions. Reviewed-by: Linus Walleij Signed-off-by: Amit Daniel Kachhap Signed-off-by: Russell King (Oracle)

ARM: 9270/1: vfp: Add hwcap for FEAT_FHM

2022-11-28T11:57:33+00:00

Floating-point half-precision multiplication (FHM) is a feature present in AArch32 state for Armv8 and is represented by ISAR6.FHM identification register. This feature denotes the presence of VFMAL and VMFSL instructions and hence adding a hwcap will enable the userspace to check it before trying to use those instructions. Reviewed-by: Linus Walleij Signed-off-by: Amit Daniel Kachhap Signed-off-by: Russell King (Oracle)

ARM: 9269/1: vfp: Add hwcap for FEAT_DotProd

2022-11-28T11:57:32+00:00

Advanced Dot product is a feature present in AArch32 state for Armv8 and is represented by ISAR6 identification register. This feature denotes the presence of UDOT and SDOT instructions and hence adding a hwcap will enable the userspace to check it before trying to use those instructions. Reviewed-by: Linus Walleij Signed-off-by: Amit Daniel Kachhap Signed-off-by: Russell King (Oracle)

ARM: 9268/1: vfp: Add hwcap FPHP and ASIMDHP for FEAT_FP16

2022-11-28T11:57:32+00:00

Floating point half-precision (FPHP) and Advanced SIMD half-precision (ASIMDHP) are VFP features (FEAT_FP16) represented by MVFR1 identification register. These capabilities can optionally exist with VFPv3 and mandatory with VFPv4. Both these new features exist for Armv8 architecture in AArch32 state. These hwcaps may be useful for the userspace to add conditional check before trying to use FEAT_FP16 feature specific instructions. Reviewed-by: Linus Walleij Signed-off-by: Amit Daniel Kachhap Signed-off-by: Russell King (Oracle)

printk: Userspace format indexing support

2021-07-19T09:57:48+00:00

We have a number of systems industry-wide that have a subset of their functionality that works as follows: 1. Receive a message from local kmsg, serial console, or netconsole; 2. Apply a set of rules to classify the message; 3. Do something based on this classification (like scheduling a remediation for the machine), rinse, and repeat. As a couple of examples of places we have this implemented just inside Facebook, although this isn't a Facebook-specific problem, we have this inside our netconsole processing (for alarm classification), and as part of our machine health checking. We use these messages to determine fairly important metrics around production health, and it's important that we get them right. While for some kinds of issues we have counters, tracepoints, or metrics with a stable interface which can reliably indicate the issue, in order to react to production issues quickly we need to work with the interface which most kernel developers naturally use when developing: printk. Most production issues come from unexpected phenomena, and as such usually the code in question doesn't have easily usable tracepoints or other counters available for the specific problem being mitigated. We have a number of lines of monitoring defence against problems in production (host metrics, process metrics, service metrics, etc), and where it's not feasible to reliably monitor at another level, this kind of pragmatic netconsole monitoring is essential. As one would expect, monitoring using printk is rather brittle for a number of reasons -- most notably that the message might disappear entirely in a new version of the kernel, or that the message may change in some way that the regex or other classification methods start to silently fail. One factor that makes this even harder is that, under normal operation, many of these messages are never expected to be hit. For example, there may be a rare hardware bug which one wants to detect if it was to ever happen again, but its recurrence is not likely or anticipated. This precludes using something like checking whether the printk in question was printed somewhere fleetwide recently to determine whether the message in question is still present or not, since we don't anticipate that it should be printed anywhere, but still need to monitor for its future presence in the long-term. This class of issue has happened on a number of occasions, causing unhealthy machines with hardware issues to remain in production for longer than ideal. As a recent example, some monitoring around blk_update_request fell out of date and caused semi-broken machines to remain in production for longer than would be desirable. Searching through the codebase to find the message is also extremely fragile, because many of the messages are further constructed beyond their callsite (eg. btrfs_printk and other module-specific wrappers, each with their own functionality). Even if they aren't, guessing the format and formulation of the underlying message based on the aesthetics of the message emitted is not a recipe for success at scale, and our previous issues with fleetwide machine health checking demonstrate as much. This provides a solution to the issue of silently changed or deleted printks: we record pointers to all printk format strings known at compile time into a new .printk_index section, both in vmlinux and modules. At runtime, this can then be iterated by looking at /printk/index/, which emits the following format, both readable by humans and able to be parsed by machines: $ head -1 vmlinux; shuf -n 5 vmlinux # filename:line function "format" <5> block/blk-settings.c:661 disk_stack_limits "%s: Warning: Device %s is misaligned\n" <4> kernel/trace/trace.c:8296 trace_create_file "Could not create tracefs '%s' entry\n" <6> arch/x86/kernel/hpet.c:144 _hpet_print_config "hpet: %s(%d):\n" <6> init/do_mounts.c:605 prepare_namespace "Waiting for root device %s...\n" <6> drivers/acpi/osl.c:1410 acpi_no_auto_serialize_setup "ACPI: auto-serialization disabled\n" This mitigates the majority of cases where we have a highly-specific printk which we want to match on, as we can now enumerate and check whether the format changed or the printk callsite disappeared entirely in userspace. This allows us to catch changes to printks we monitor earlier and decide what to do about it before it becomes problematic. There is no additional runtime cost for printk callers or printk itself, and the assembly generated is exactly the same. Signed-off-by: Chris Down Cc: Petr Mladek Cc: Jessica Yu Cc: Sergey Senozhatsky Cc: John Ogness Cc: Steven Rostedt Cc: Greg Kroah-Hartman Cc: Johannes Weiner Cc: Kees Cook Reviewed-by: Petr Mladek Tested-by: Petr Mladek Reported-by: kernel test robot Acked-by: Andy Shevchenko Acked-by: Jessica Yu # for module.{c,h} Signed-off-by: Petr Mladek Link: https://lore.kernel.org/r/e42070983637ac5e384f17fbdbe86d19c7b212a5.1623775748.git.chris@chrisdown.name