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Michael Ellerman b91eb51824 powerpc/64s: Fix crash in load_fp_state() due to fpexc_mode 
The recent commit 01eb01877f ("powerpc/64s: Fix restore_math
unnecessarily changing MSR") changed some of the handling of floating
point/vector restore.

In particular it caused current->thread.fpexc_mode to be copied into
the current MSR (via msr_check_and_set()), rather than just into
regs->msr (which is moved into MSR on return to userspace).

This can lead to a crash in the kernel if we take a floating point
exception when restoring FPSCR:

  Oops: Exception in kernel mode, sig: 8 [#1]
  LE PAGE_SIZE=64K MMU=Radix SMP NR_CPUS=2048 NUMA PowerNV
  Modules linked in:
  CPU: 3 PID: 101213 Comm: ld64.so.2 Not tainted 5.9.0-rc1-00098-g18445bf405cb-dirty #9
  NIP:  c00000000000fbb4 LR: c00000000001a7ac CTR: c000000000183570
  REGS: c0000016b7cfb3b0 TRAP: 0700   Not tainted  (5.9.0-rc1-00098-g18445bf405cb-dirty)
  MSR:  900000000290b933 <SF,HV,VEC,VSX,EE,FP,ME,IR,DR,RI,LE>  CR: 44002444  XER: 00000000
  CFAR: c00000000001a7a8 IRQMASK: 1
  GPR00: c00000000001ae40 c0000016b7cfb640 c0000000011b7f00 c000001542a0f740
  GPR04: c000001542a0f720 c000001542a0eb00 0000000000000900 c000001542a0eb00
  GPR08: 000000000000000a 0000000000002000 9000000000009033 0000000000000000
  GPR12: 0000000000004000 c0000017ffffd900 0000000000000001 c000000000df5a58
  GPR16: c000000000e19c18 c0000000010e1123 0000000000000001 c000000000e1a638
  GPR20: 0000000000000000 c0000000044b1d00 0000000000000000 c000001542a0f2a0
  GPR24: 00000016c7fe0000 c000001542a0f720 c000000001c93da0 c000000000fe5f28
  GPR28: c000001542a0f720 0000000000800000 c0000016b7cfbe90 0000000002802900
  NIP load_fp_state+0x4/0x214
  LR  restore_math+0x17c/0x1f0
  Call Trace:
    0xc0000016b7cfb680 (unreliable)
    __switch_to+0x330/0x460
    __schedule+0x318/0x920
    schedule+0x74/0x140
    schedule_timeout+0x318/0x3f0
    wait_for_completion+0xc8/0x210
    call_usermodehelper_exec+0x234/0x280
    do_coredump+0xedc/0x13c0
    get_signal+0x1d4/0xbe0
    do_notify_resume+0x1a0/0x490
    interrupt_exit_user_prepare+0x1c4/0x230
    interrupt_return+0x14/0x1c0
  Instruction dump:
  ebe10168 e88101a0 7c8ff120 382101e0 e8010010 7c0803a6 4e800020 790605c4
  782905c4 7c0008a8 7c0008a8 c8030200 <fffe058e> 48000088 c8030000 c8230010

Fix it by only loading the fpexc_mode value into regs->msr.

Also add a comment to explain that although VSX is subject to the
value of fpexc_mode, we don't have to handle that separately because
we only allow VSX to be enabled if FP is also enabled.

Fixes: 01eb01877f ("powerpc/64s: Fix restore_math unnecessarily changing MSR")
Reported-by: Milton Miller <miltonm@us.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Reviewed-by: Nicholas Piggin <npiggin@gmail.com>
Link: https://lore.kernel.org/r/20200825093424.3967813-1-mpe@ellerman.id.au
2020-08-27 17:41:39 +10:00
arch powerpc/64s: Fix crash in load_fp_state() due to fpexc_mode 2020-08-27 17:41:39 +10:00
block block-5.9-2020-08-14 2020-08-15 20:36:42 -07:00
certs .gitignore: add SPDX License Identifier 2020-03-25 11:50:48 +01:00
crypto Merge branch 'linus' of git://git.kernel.org/pub/scm/linux/kernel/git/herbert/crypto-2.6 2020-08-14 13:09:15 -07:00
Documentation Documentation/powerpc: fix malformed table in syscall64-abi 2020-08-27 17:40:55 +10:00
drivers video: fbdev: controlfb: Fix build for COMPILE_TEST=y && PPC_PMAC=n 2020-08-27 17:40:50 +10:00
fs io_uring-5.9-2020-08-15 2020-08-16 10:55:12 -07:00
include Revert "powerpc/64s: Remove PROT_SAO support" 2020-08-24 14:12:53 +10:00
init OpenRISC updates for 5.9 2020-08-14 14:04:53 -07:00
ipc ipc/shm.c: remove the superfluous break 2020-08-12 10:58:02 -07:00
kernel io_uring-5.9-2020-08-15 2020-08-16 10:55:12 -07:00
lib iomap: constify ioreadX() iomem argument (as in generic implementation) 2020-08-14 19:56:57 -07:00
LICENSES LICENSES: Rename other to deprecated 2019-05-03 06:34:32 -06:00
mm Revert "powerpc/64s: Remove PROT_SAO support" 2020-08-24 14:12:53 +10:00
net 9p pull request for inclusion in 5.9 2020-08-15 08:34:36 -07:00
samples Kbuild updates for v5.9 2020-08-09 14:10:26 -07:00
scripts Kconfig updates for v5.9 2020-08-14 11:04:45 -07:00
security Merge branch 'akpm' (patches from Andrew) 2020-08-12 11:24:12 -07:00
sound sound fixes for 5.9-rc1 2020-08-14 15:58:57 -07:00
tools selftests/powerpc: Update PROT_SAO test to skip ISA 3.1 2020-08-24 14:12:54 +10:00
usr Merge branch 'work.fdpic' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs 2020-08-07 13:29:39 -07:00
virt Merge branch 'akpm' (patches from Andrew) 2020-08-12 11:24:12 -07:00
.clang-format block: add bio_for_each_bvec_all() 2020-05-25 11:25:24 +02:00
.cocciconfig
.get_maintainer.ignore Opt out of scripts/get_maintainer.pl 2019-05-16 10:53:40 -07:00
.gitattributes .gitattributes: use 'dts' diff driver for dts files 2019-12-04 19:44:11 -08:00
.gitignore .gitignore: Add ZSTD-compressed files 2020-07-31 11:50:49 +02:00
.mailmap mailmap: add entry for Greg Kurz 2020-08-14 19:56:56 -07:00
COPYING COPYING: state that all contributions really are covered by this file 2020-02-10 13:32:20 -08:00
CREDITS CREDITS: Replace HTTP links with HTTPS ones 2020-07-23 14:53:58 -06:00
Kbuild kbuild: rename hostprogs-y/always to hostprogs/always-y 2020-02-04 01:53:07 +09:00
Kconfig kbuild: ensure full rebuild when the compiler is updated 2020-05-12 13:28:33 +09:00
MAINTAINERS perf tools changes for v5.9: 2nd batch 2020-08-15 11:17:15 -07:00
Makefile Linux 5.9-rc1 2020-08-16 13:04:57 -07:00
README Drop all 00-INDEX files from Documentation/ 2018-09-09 15:08:58 -06:00

README 

Linux kernel
============

There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.  The formatted documentation can also be read online at:

    https://www.kernel.org/doc/html/latest/

There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.