linux-dev/arch/powerpc/kernel/interrupt_64.S, branch linus/master

powerpc: Replace PPC64_ELF_ABI_v{1/2} by CONFIG_PPC64_ELF_ABI_V{1/2}

2022-05-19T13:11:29Z

Replace all uses of PPC64_ELF_ABI_v1 and PPC64_ELF_ABI_v2 by resp CONFIG_PPC64_ELF_ABI_V1 and CONFIG_PPC64_ELF_ABI_V2. Signed-off-by: Christophe Leroy Signed-off-by: Michael Ellerman Link: https://lore.kernel.org/r/ba13d59e8c50bc9aa6328f1c7f0c0d0278e0a3a7.1652074503.git.christophe.leroy@csgroup.eu

powerpc/64: remove system call instruction emulation

2022-05-05T14:00:20Z

emulate_step() instruction emulation including sc instruction emulation initially appeared in xmon. It was then moved into sstep.c where kprobes could use it too, and later hw_breakpoint and uprobes started to use it. Until uprobes, the only instruction emulation users were for kernel mode instructions. - xmon only steps / breaks on kernel addresses. - kprobes is kernel only. - hw_breakpoint only emulates kernel instructions, single steps user. At one point, there was support for the kernel to execute sc instructions, although that is long removed and it's not clear whether there were any in-tree users. So system call emulation is not required by the above users. uprobes uses emulate_step and it appears possible to emulate sc instruction in userspace. Userspace system call emulation is broken and it's not clear it ever worked well. The big complication is that userspace takes an interrupt to the kernel to emulate the instruction. The user->kernel interrupt sets up registers and interrupt stack frame expecting to return to userspace, then system call instruction emulation re-directs that stack frame to the kernel, early in the system call interrupt handler. This means the interrupt return code takes the kernel->kernel restore path, which does not restore everything as the system call interrupt handler would expect coming from userspace. regs->iamr appears to get lost for example, because the kernel->kernel return does not restore the user iamr. Accounting such as irqflags tracing and CPU accounting does not get flipped back to user mode as the system call handler expects, so those appear to enter the kernel twice without returning to userspace. These things may be individually fixable with various complication, but it is a big complexity for unclear real benefit. Furthermore, it is not possible to single step a system call instruction since it causes an interrupt. As such, a separate patch disables probing on system call instructions. This patch removes system call emulation and disables stepping system calls. Signed-off-by: Nicholas Piggin [minor commit log edit, and also get rid of '#ifdef CONFIG_PPC64'] Signed-off-by: Naveen N. Rao Signed-off-by: Michael Ellerman Link: https://lore.kernel.org/r/a412e3b3791ed83de18704c8d90f492e7a0049c0.1648648712.git.naveen.n.rao@linux.vnet.ibm.com

powerpc/64s: Mask SRR0 before checking against the masked NIP

2022-01-17T23:25:18Z

Commit 314f6c23dd8d ("powerpc/64s: Mask NIP before checking against SRR0") masked off the low 2 bits of the NIP value in the interrupt stack frame in case they are non-zero and mis-compare against a SRR0 register value of a CPU which always reads back 0 from the 2 low bits which are reserved. This now causes the opposite problem that an implementation which does implement those bits in SRR0 will mis-compare against the masked NIP value in which they have been cleared. QEMU is one such implementation, and this is allowed by the architecture. This can be triggered by sigfuz by setting low bits of PT_NIP in the signal context. Fix this for now by masking the SRR0 bits as well. Cleaner is probably to sanitise these values before putting them in registers or stack, but this is the quick and backportable fix. Fixes: 314f6c23dd8d ("powerpc/64s: Mask NIP before checking against SRR0") Signed-off-by: Nicholas Piggin Signed-off-by: Michael Ellerman Link: https://lore.kernel.org/r/20220117134403.2995059-1-npiggin@gmail.com

powerpc/64s: Use EMIT_WARN_ENTRY for SRR debug warnings

2021-12-24T23:56:01Z

When CONFIG_PPC_RFI_SRR_DEBUG=y we check the SRR values before returning from interrupts. This is done in asm using EMIT_BUG_ENTRY, and passing BUGFLAG_WARNING. However that fails to create an exception table entry for the warning, and so do_program_check() fails the exception table search and proceeds to call _exception(), resulting in an oops like: Oops: Exception in kernel mode, sig: 5 [#1] LE PAGE_SIZE=64K MMU=Radix SMP NR_CPUS=2048 NUMA pSeries Modules linked in: CPU: 2 PID: 1204 Comm: sigreturn_unali Tainted: P 5.16.0-rc2-00194-g91ca3d4f77c5 #12 NIP: c00000000000c5b0 LR: 0000000000000000 CTR: 0000000000000000 ... NIP [c00000000000c5b0] system_call_common+0x150/0x268 LR [0000000000000000] 0x0 Call Trace: [c00000000db73e10] [c00000000000c558] system_call_common+0xf8/0x268 (unreliable) ... Instruction dump: 7cc803a6 888d0931 2c240000 4082001c 38800000 988d0931 e8810170 e8a10178 7c9a03a6 7cbb03a6 7d7a02a6 e9810170 <7f0b6088> 7d7b02a6 e9810178 7f0b6088 We should instead use EMIT_WARN_ENTRY, which creates an exception table entry for the warning, allowing the warning to be correctly recognised, and the code to resume after printing the warning. Note however that because this warning is buried deep in the interrupt return path, we are not able to recover from it (due to MSR_RI being clear), so we still end up in die() with an unrecoverable exception. Fixes: 59dc5bfca0cb ("powerpc/64s: avoid reloading (H)SRR registers if they are still valid") Signed-off-by: Michael Ellerman Link: https://lore.kernel.org/r/20211221135101.2085547-2-mpe@ellerman.id.au

powerpc/64s: Mask NIP before checking against SRR0

2021-12-24T23:55:55Z

When CONFIG_PPC_RFI_SRR_DEBUG=y we check that NIP and SRR0 match when returning from interrupts. This can trigger falsely if NIP has either of its two low bits set via sigreturn or ptrace, while SRR0 has its low two bits masked in hardware. As a quick fix make sure to mask the low bits before doing the check. Fixes: 59dc5bfca0cb ("powerpc/64s: avoid reloading (H)SRR registers if they are still valid") Reported-by: Sachin Sant Signed-off-by: Michael Ellerman Tested-by: Sachin Sant Link: https://lore.kernel.org/r/20211221135101.2085547-1-mpe@ellerman.id.au

powerpc/64/asm: Do not reassign labels

2021-12-23T11:35:12Z

The LLVM integrated assembler really does not like us reassigning things to the same label: :7:9: error: invalid reassignment of non-absolute variable 'fs_label' This happens across a bunch of platforms: https://github.com/ClangBuiltLinux/linux/issues/1043 https://github.com/ClangBuiltLinux/linux/issues/1008 https://github.com/ClangBuiltLinux/linux/issues/920 https://github.com/ClangBuiltLinux/linux/issues/1050 There is no hope of getting this fixed in LLVM (see https://github.com/ClangBuiltLinux/linux/issues/1043#issuecomment-641571200 and https://bugs.llvm.org/show_bug.cgi?id=47798#c1 ) so if we want to build with LLVM_IAS, we need to hack around it ourselves. For us the big problem comes from this: \#define USE_FIXED_SECTION(sname) \ fs_label = start_##sname; \ fs_start = sname##_start; \ use_ftsec sname; \#define USE_TEXT_SECTION() fs_label = start_text; \ fs_start = text_start; \ .text and in particular fs_label. This works around it by not setting those 'variables' and requiring that users of the variables instead track for themselves what section they are in. This isn't amazing, by any stretch, but it gets us further in the compilation. Note that even though users have to keep track of the section, using a wrong one produces an error with both binutils and llvm which prevents from using wrong section at the compile time: llvm error example: AS arch/powerpc/kernel/head_64.o :0: error: Cannot represent a difference across sections make[3]: *** [/home/aik/p/kernels-llvm/llvm/scripts/Makefile.build:388: arch/powerpc/kernel/head_64.o] Error 1 binutils error example: /home/aik/p/kernels-llvm/llvm/arch/powerpc/kernel/exceptions-64s.S: Assembler messages: /home/aik/p/kernels-llvm/llvm/arch/powerpc/kernel/exceptions-64s.S:1974: Error: can't resolve `system_call_common' {.text section} - `start_r eal_vectors' {.head.text.real_vectors section} make[3]: *** [/home/aik/p/kernels-llvm/llvm/scripts/Makefile.build:388: arch/powerpc/kernel/head_64.o] Error 1 Signed-off-by: Daniel Axtens Signed-off-by: Alexey Kardashevskiy Signed-off-by: Michael Ellerman Link: https://lore.kernel.org/r/20211221055904.555763-5-aik@ozlabs.ru

powerpc: flexible GPR range save/restore macros

2021-11-29T12:15:20Z

Introduce macros that operate on a (start, end) range of GPRs, which reduces lines of code and need to do mental arithmetic while reading the code. Signed-off-by: Nicholas Piggin Reviewed-by: Segher Boessenkool Reviewed-by: Christophe Leroy Signed-off-by: Michael Ellerman Link: https://lore.kernel.org/r/20211022061322.2671178-1-npiggin@gmail.com

powerpc/64s: system call scv tabort fix for corrupt irq soft-mask state

2021-09-13T12:34:11Z

If a system call is made with a transaction active, the kernel immediately aborts it and returns. scv system calls disable irqs even earlier in their interrupt handler, and tabort_syscall does not fix this up. This can result in irq soft-mask state being messed up on the next kernel entry, and crashing at BUG_ON(arch_irq_disabled_regs(regs)) in the kernel exit handlers, or possibly worse. This can't easily be fixed in asm because at this point an async irq may have hit, which is soft-masked and marked pending. The pending interrupt has to be replayed before returning to userspace. The fix is to move the tabort_syscall code to C in the main syscall handler, and just skip the system call but otherwise return as usual, which will take care of the pending irqs. This also does a bunch of other things including possible signal delivery to the process, but the doomed transaction should still be aborted when it is eventually returned to. The sc system call path is changed to use the new C function as well to reduce code and path differences. This slows down how quickly system calls are aborted when called while a transaction is active, which could potentially impact TM performance. But making any system call is already bad for performance, and TM is on the way out, so go with simpler over faster. Fixes: 7fa95f9adaee7 ("powerpc/64s: system call support for scv/rfscv instructions") Reported-by: Eirik Fuller Signed-off-by: Nicholas Piggin [mpe: Use #ifdef rather than IS_ENABLED() to fix build error on 32-bit] Signed-off-by: Michael Ellerman Link: https://lore.kernel.org/r/20210903125707.1601269-1-npiggin@gmail.com

powerpc/64e: Fix system call illegal mtmsrd instruction

2021-07-06T09:58:54Z

BookE does not have mtmsrd, switch to use wrteei to enable MSR[EE]. Fixes: dd152f70bdc1 ("powerpc/64s: system call avoid setting MSR[RI] until we set MSR[EE]") Reported-by: Christian Zigotzky Signed-off-by: Nicholas Piggin Signed-off-by: Michael Ellerman Link: https://lore.kernel.org/r/20210706051310.608992-1-npiggin@gmail.com

powerpc/64s: move ret_from_fork etc above __end_soft_masked

2021-06-30T12:21:20Z

Code which runs with interrupts enabled should be moved above __end_soft_masked where possible, because maskable interrupts that hit below that symbol will need to consult the soft mask table, which is an extra cost. Signed-off-by: Nicholas Piggin Signed-off-by: Michael Ellerman Link: https://lore.kernel.org/r/20210630074621.2109197-10-npiggin@gmail.com