From c9debbd1a5b84014d8651da82ca30651d83ca322 Mon Sep 17 00:00:00 2001 From: Vaibhav Jain Date: Fri, 18 May 2018 15:12:23 +0530 Subject: cxl: Disable prefault_mode in Radix mode commit b6c84ba22ff3a198eb8d5552cf9b8fda1d792e54 upstream. Currently we see a kernel-oops reported on Power-9 while attaching a context to an AFU, with radix-mode and sysfs attr 'prefault_mode' set to anything other than 'none'. The backtrace of the oops is of this form: Unable to handle kernel paging request for data at address 0x00000080 Faulting instruction address: 0xc00800000bcf3b20 cpu 0x1: Vector: 300 (Data Access) at [c00000037f003800] pc: c00800000bcf3b20: cxl_load_segment+0x178/0x290 [cxl] lr: c00800000bcf39f0: cxl_load_segment+0x48/0x290 [cxl] sp: c00000037f003a80 msr: 9000000000009033 dar: 80 dsisr: 40000000 current = 0xc00000037f280000 paca = 0xc0000003ffffe600 softe: 3 irq_happened: 0x01 pid = 3529, comm = afp_no_int cxl_prefault+0xfc/0x248 [cxl] process_element_entry_psl9+0xd8/0x1a0 [cxl] cxl_attach_dedicated_process_psl9+0x44/0x130 [cxl] native_attach_process+0xc0/0x130 [cxl] afu_ioctl+0x3f4/0x5e0 [cxl] do_vfs_ioctl+0xdc/0x890 ksys_ioctl+0x68/0xf0 sys_ioctl+0x40/0xa0 system_call+0x58/0x6c The issue is caused as on Power-8 the AFU attr 'prefault_mode' was used to improve initial storage fault performance by prefaulting process segments. However on Power-9 with radix mode we don't have Storage-Segments that we can prefault. Also prefaulting process Pages will be too costly and fine-grained. Hence, since the prefaulting mechanism doesn't makes sense of radix-mode, this patch updates prefault_mode_store() to not allow any other value apart from CXL_PREFAULT_NONE when radix mode is enabled. Fixes: f24be42aab37 ("cxl: Add psl9 specific code") Cc: stable@vger.kernel.org # v4.12+ Signed-off-by: Vaibhav Jain Acked-by: Frederic Barrat Acked-by: Andrew Donnellan Signed-off-by: Michael Ellerman Signed-off-by: Greg Kroah-Hartman --- Documentation/ABI/testing/sysfs-class-cxl | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) (limited to 'Documentation/ABI') diff --git a/Documentation/ABI/testing/sysfs-class-cxl b/Documentation/ABI/testing/sysfs-class-cxl index 640f65e79ef1..267920a1874b 100644 --- a/Documentation/ABI/testing/sysfs-class-cxl +++ b/Documentation/ABI/testing/sysfs-class-cxl @@ -69,7 +69,9 @@ Date: September 2014 Contact: linuxppc-dev@lists.ozlabs.org Description: read/write Set the mode for prefaulting in segments into the segment table - when performing the START_WORK ioctl. Possible values: + when performing the START_WORK ioctl. Only applicable when + running under hashed page table mmu. + Possible values: none: No prefaulting (default) work_element_descriptor: Treat the work element descriptor as an effective address and -- cgit v1.2.3