linux-dev/arch/powerpc/kernel/syscall_64.c, branch linus/master

powerpc/syscall: Rename syscall_64.c into interrupt.c

2021-02-11T12:35:10Z

syscall_64.c will be reused almost as is for PPC32. As this file also contains functions to handle other types of interrupts rename it interrupt.c Signed-off-by: Christophe Leroy Reviewed-by: Nicholas Piggin Signed-off-by: Michael Ellerman Link: https://lore.kernel.org/r/cddc2deaa8f049d3ec419738e69804934919b935.1612796617.git.christophe.leroy@csgroup.eu

powerpc/64: move account_stolen_time into its own function

2021-02-08T13:10:49Z

This will be used by interrupt entry as well. Signed-off-by: Nicholas Piggin Signed-off-by: Michael Ellerman Link: https://lore.kernel.org/r/20210130130852.2952424-38-npiggin@gmail.com

powerpc/64s: move context tracking exit to interrupt exit path

2021-02-08T13:10:49Z

The interrupt handler wrapper functions are not the ideal place to maintain context tracking because after they return, the low level exit code must then determine if there are interrupts to replay, or if the task should be preempted, etc. Those paths (e.g., schedule_user) include their own exception_enter/exit pairs to fix this up but it's a bit hacky (see schedule_user() comments). Ideally context tracking will go to user mode only when there are no more interrupts or context switches or other exit processing work to handle. 64e can not do this because it does not use the C interrupt exit code. Signed-off-by: Nicholas Piggin Signed-off-by: Michael Ellerman Link: https://lore.kernel.org/r/20210130130852.2952424-36-npiggin@gmail.com

powerpc/64: context tracking remove _TIF_NOHZ

2021-02-08T13:02:12Z

Add context tracking to the system call handler explicitly, and remove _TIF_NOHZ. This improves system call performance when nohz_full is enabled. On a POWER9, gettid scv system call cost on a nohz_full CPU improves from 1129 cycles to 1004 cycles and on a housekeeping CPU from 550 cycles to 430 cycles. Signed-off-by: Nicholas Piggin Signed-off-by: Michael Ellerman Link: https://lore.kernel.org/r/20210130130852.2952424-31-npiggin@gmail.com

powerpc: convert interrupt handlers to use wrappers

2021-02-08T13:02:12Z

Signed-off-by: Nicholas Piggin Signed-off-by: Michael Ellerman Link: https://lore.kernel.org/r/20210130130852.2952424-29-npiggin@gmail.com

powerpc/64s: interrupt exit improve bounding of interrupt recursion

2021-02-08T13:02:07Z

When replaying pending soft-masked interrupts when an interrupt returns to an irqs-enabled context, there is a special case required if this was an asynchronous interrupt to avoid unbounded interrupt recursion. This case was not tested for in the case the asynchronous interrupt hit in user context, because a subsequent nested interrupt would by definition hit in kernel mode, which then exits via the kernel path which does test this case. There is no reason to allow this for such interrupts. While recursion is bounded at the next level, it's simpler and uses less stack to apply the replay logic consistently. This also expands the comment which was really pretty poor and didn't explain the problem (I can say that because I wrote it). Signed-off-by: Nicholas Piggin Signed-off-by: Michael Ellerman Link: https://lore.kernel.org/r/20210130130852.2952424-2-npiggin@gmail.com

powerpc/book3s64/pkeys: Optimize KUAP and KUEP feature disabled case

2020-12-03T14:01:28Z

If FTR_BOOK3S_KUAP is disabled, kernel will continue to run with the same AMR value with which it was entered. Hence there is a high chance that we can return without restoring the AMR value. This also helps the case when applications are not using the pkey feature. In this case, different applications will have the same AMR values and hence we can avoid restoring AMR in this case too. Also avoid isync() if not really needed. Do the same for IAMR. null-syscall benchmark results: With smap/smep disabled: Without patch: 957.95 ns 2778.17 cycles With patch: 858.38 ns 2489.30 cycles With smap/smep enabled: Without patch: 1017.26 ns 2950.36 cycles With patch: 1021.51 ns 2962.44 cycles Signed-off-by: Aneesh Kumar K.V Signed-off-by: Michael Ellerman Link: https://lore.kernel.org/r/20201127044424.40686-23-aneesh.kumar@linux.ibm.com

powerpc/book3s64/pkeys: Store/restore userspace AMR/IAMR correctly on entry and exit from kernel

2020-12-03T14:01:25Z

This prepare kernel to operate with a different value than userspace AMR/IAMR. For this, AMR/IAMR need to be saved and restored on entry and return from the kernel. With KUAP we modify kernel AMR when accessing user address from the kernel via copy_to/from_user interfaces. We don't need to modify IAMR value in similar fashion. If MMU_FTR_PKEY is enabled we need to save AMR/IAMR in pt_regs on entering kernel from userspace. If not we can assume that AMR/IAMR is not modified from userspace. We need to save AMR if we have MMU_FTR_BOOK3S_KUAP feature enabled and we are interrupted within kernel. This is required so that if we get interrupted within copy_to/from_user we continue with the right AMR value. If we hae MMU_FTR_BOOK3S_KUEP enabled we need to restore IAMR on return to userspace beause kernel will be running with a different IAMR value. Signed-off-by: Aneesh Kumar K.V Reviewed-by: Sandipan Das Signed-off-by: Michael Ellerman Link: https://lore.kernel.org/r/20201127044424.40686-11-aneesh.kumar@linux.ibm.com

powerpc: Only include kup-radix.h for 64-bit Book3S

2020-11-19T12:47:20Z

In kup.h we currently include kup-radix.h for all 64-bit builds, which includes Book3S and Book3E. The latter doesn't make sense, Book3E never uses the Radix MMU. This has worked up until now, but almost by accident, and the recent uaccess flush changes introduced a build breakage on Book3E because of the bad structure of the code. So disentangle things so that we only use kup-radix.h for Book3S. This requires some more stubs in kup.h and fixing an include in syscall_64.c. Signed-off-by: Michael Ellerman

Merge branch 'scv' support into next

2020-07-23T07:43:44Z

From Nick's cover letter: Linux powerpc new system call instruction and ABI System Call Vectored (scv) ABI ============================== The scv instruction is introduced with POWER9 / ISA3, it comes with an rfscv counter-part. The benefit of these instructions is performance (trading slower SRR0/1 with faster LR/CTR registers, and entering the kernel with MSR[EE] and MSR[RI] left enabled, which can reduce MSR updates. The scv instruction has 128 levels (not enough to cover the Linux system call space). Assignment and advertisement ---------------------------- The proposal is to assign scv levels conservatively, and advertise them with HWCAP feature bits as we add support for more. Linux has not enabled FSCR[SCV] yet, so executing the scv instruction will cause the kernel to log a "SCV facility unavilable" message, and deliver a SIGILL with ILL_ILLOPC to the process. Linux has defined a HWCAP2 bit PPC_FEATURE2_SCV for SCV support, but does not set it. This change allocates the zero level ('scv 0'), advertised with PPC_FEATURE2_SCV, which will be used to provide normal Linux system calls (equivalent to 'sc'). Attempting to execute scv with other levels will cause a SIGILL to be delivered the same as before, but will not log a "SCV facility unavailable" message (because the processor facility is enabled). Calling convention ------------------ The proposal is for scv 0 to provide the standard Linux system call ABI with the following differences from sc convention[1]: - LR is to be volatile across scv calls. This is necessary because the scv instruction clobbers LR. From previous discussion, this should be possible to deal with in GCC clobbers and CFI. - cr1 and cr5-cr7 are volatile. This matches the C ABI and would allow the kernel system call exit to avoid restoring the volatile cr registers (although we probably still would anyway to avoid information leaks). - Error handling: The consensus among kernel, glibc, and musl is to move to using negative return values in r3 rather than CR0[SO]=1 to indicate error, which matches most other architectures, and is closer to a function call. Notes ----- - r0,r4-r8 are documented as volatile in the ABI, but the kernel patch as submitted currently preserves them. This is to leave room for deciding which way to go with these. Some small benefit was found by preserving them[1] but I'm not convinced it's worth deviating from the C function call ABI just for this. Release code should follow the ABI. Previous discussions: https://lists.ozlabs.org/pipermail/linuxppc-dev/2020-April/208691.html https://lists.ozlabs.org/pipermail/linuxppc-dev/2020-April/209268.html [1] https://github.com/torvalds/linux/blob/master/Documentation/powerpc/syscall64-abi.rst [2] https://lists.ozlabs.org/pipermail/linuxppc-dev/2020-April/209263.html