Le 18/05/2018 à 11:42, Vaibhav Jain a écrit :

From: Vaibhav Jain vaibhav@linux.ibm.com

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

<snip> [c00000037f003af0] c00800000bcf4424 cxl_prefault+0xfc/0x248 [cxl] [c00000037f003b50] c00800000bcf8a40 process_element_entry_psl9+0xd8/0x1a0 [cxl] [c00000037f003b90] c00800000bcf944c cxl_attach_dedicated_process_psl9+0x44/0x130 [cxl] [c00000037f003bd0] c00800000bcf5448 native_attach_process+0xc0/0x130 [cxl] [c00000037f003c50] c00800000bcf16cc afu_ioctl+0x3f4/0x5e0 [cxl] [c00000037f003d00] c00000000039d98c do_vfs_ioctl+0xdc/0x890 [c00000037f003da0] c00000000039e1a8 ksys_ioctl+0x68/0xf0 [c00000037f003df0] c00000000039e270 sys_ioctl+0x40/0xa0 [c00000037f003e30] c00000000000b320 system_call+0x58/0x6c --- Exception: c01 (System Call) at 0000000010053bb0

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.

Cc: stable@vger.kernel.org Fixes: f24be42aab37 ("cxl: Add psl9 specific code") Signed-off-by: Vaibhav Jain vaibhav@linux.ibm.com

---

Thanks! Acked-by: Frederic Barrat fbarrat@linux.vnet.ibm.com

Change-log:

Resend -> Updated the commit description to add more info on the issue seen [Andrew]

---

Documentation/ABI/testing/sysfs-class-cxl | 4 +++- drivers/misc/cxl/sysfs.c | 16 ++++++++++++---- 2 files changed, 15 insertions(+), 5 deletions(-)

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
  

diff --git a/drivers/misc/cxl/sysfs.c b/drivers/misc/cxl/sysfs.c index 4b5a4c5d3c01..629e2e156412 100644 --- a/drivers/misc/cxl/sysfs.c +++ b/drivers/misc/cxl/sysfs.c @@ -353,12 +353,20 @@ static ssize_t prefault_mode_store(struct device *device, struct cxl_afu *afu = to_cxl_afu(device); enum prefault_modes mode = -1;

• if (!strncmp(buf, "work_element_descriptor", 23))

• mode = CXL_PREFAULT_WED;
  

• if (!strncmp(buf, "all", 3))

• mode = CXL_PREFAULT_ALL;
  

  if (!strncmp(buf, "none", 4)) mode = CXL_PREFAULT_NONE;

• else {

• if (!radix_enabled()) {
  

• 	/* only allowed when not in radix mode */
  

• 	if (!strncmp(buf, "work_element_descriptor", 23))
  

• 		mode = CXL_PREFAULT_WED;
  

• 	if (!strncmp(buf, "all", 3))
  

• 		mode = CXL_PREFAULT_ALL;
  

• } else {
  

• 	dev_err(device, "Cannot prefault with radix enabled\n");
  

• }
  

• }

  if (mode == -1) return -EINVAL;