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Suzuki K Poulose da64ec3259 arm64: nofpsmid: Handle TIF_FOREIGN_FPSTATE flag cleanly 
commit 52f73c383b upstream.

We detect the absence of FP/SIMD after an incapable CPU is brought up,
and by then we have kernel threads running already with TIF_FOREIGN_FPSTATE set
which could be set for early userspace applications (e.g, modprobe triggered
from initramfs) and init. This could cause the applications to loop forever in
do_nofity_resume() as we never clear the TIF flag, once we now know that
we don't support FP.

Fix this by making sure that we clear the TIF_FOREIGN_FPSTATE flag
for tasks which may have them set, as we would have done in the normal
case, but avoiding touching the hardware state (since we don't support any).

Also to make sure we handle the cases seemlessly we categorise the
helper functions to two :
 1) Helpers for common core code, which calls into take appropriate
    actions without knowing the current FPSIMD state of the CPU/task.

    e.g fpsimd_restore_current_state(), fpsimd_flush_task_state(),
        fpsimd_save_and_flush_cpu_state().

    We bail out early for these functions, taking any appropriate actions
    (e.g, clearing the TIF flag) where necessary to hide the handling
    from core code.

 2) Helpers used when the presence of FP/SIMD is apparent.
    i.e, save/restore the FP/SIMD register state, modify the CPU/task
    FP/SIMD state.
    e.g,

    fpsimd_save(), task_fpsimd_load() - save/restore task FP/SIMD registers

    fpsimd_bind_task_to_cpu()  \
                                - Update the "state" metadata for CPU/task.
    fpsimd_bind_state_to_cpu() /

    fpsimd_update_current_state() - Update the fp/simd state for the current
                                    task from memory.

    These must not be called in the absence of FP/SIMD. Put in a WARNING
    to make sure they are not invoked in the absence of FP/SIMD.

KVM also uses the TIF_FOREIGN_FPSTATE flag to manage the FP/SIMD state
on the CPU. However, without FP/SIMD support we trap all accesses and
inject undefined instruction. Thus we should never "load" guest state.
Add a sanity check to make sure this is valid.

Fixes: 82e0191a1a ("arm64: Support systems without FP/ASIMD")
Cc: Will Deacon <will@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Reviewed-by: Ard Biesheuvel <ardb@kernel.org>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Acked-by: Marc Zyngier <maz@kernel.org>
Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Signed-off-by: Will Deacon <will@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
History 2020-02-14 16:53:04 -05:00
arch arm64: nofpsmid: Handle TIF_FOREIGN_FPSTATE flag cleanly 2020-02-14 16:53:04 -05:00
block compat: scsi: sg: fix v3 compat read/write interface 2020-02-11 04:37:17 -08:00
certs certs: Add wrapper function to check blacklisted binary hash 2019-11-12 12:25:50 +11:00
crypto crypto: api - Fix race condition in crypto_spawn_alg 2020-02-11 04:37:01 -08:00
Documentation PM / devfreq: Add new name attribute for sysfs 2020-02-04 18:18:01 +00:00
drivers iommu/arm-smmu-v3: Populate VMID field for CMDQ_OP_TLBI_NH_VA 2020-02-14 16:53:02 -05:00
fs NFSv4.0: nfs4_do_fsinfo() should not do implicit lease renewals 2020-02-14 16:52:59 -05:00
include RDMA/uverbs: Verify MR access flags 2020-02-14 16:52:56 -05:00
init Revert "um: Enable CONFIG_CONSTRUCTORS" 2020-02-01 09:33:00 +00:00
ipc ipc/msg.c: consolidate all xxxctl_down() functions 2020-02-11 04:36:39 -08:00
kernel sched/uclamp: Fix a bug in propagating uclamp value in new cgroups 2020-02-14 16:53:03 -05:00
lib lib/test_kasan.c: fix memory leak in kmalloc_oob_krealloc_more() 2020-02-11 04:36:45 -08:00
LICENSES LICENSES: Rename other to deprecated 2019-05-03 06:34:32 -06:00
mm mm/mmu_gather: invalidate TLB correctly on batch allocation failure and flush 2020-02-11 04:37:14 -08:00
net bpf, sockmap: Check update requirements after locking 2020-02-14 16:53:00 -05:00
samples samples/bpf: Reintroduce missed build targets 2020-02-11 04:37:00 -08:00
scripts scripts/find-unused-docs: Fix massive false positives 2020-02-11 04:36:53 -08:00
security broken ping to ipv6 linklocal addresses on debian buster 2020-02-11 04:37:16 -08:00
sound ASoC: Intel: skl_hda_dsp_common: Fix global-out-of-bounds bug 2020-02-11 04:37:21 -08:00
tools tools/power/acpi: fix compilation error 2020-02-14 16:53:02 -05:00
usr gen_initramfs_list.sh: fix 'bad variable name' error 2020-01-04 00:00:48 +09:00
virt KVM: arm64: Treat emulated TVAL TimerValue as a signed 32-bit integer 2020-02-14 16:53:04 -05:00
.clang-format clang-format: Update with the latest for_each macro list 2019-08-31 10:00:51 +02:00
.cocciconfig scripts: add Linux .cocciconfig for coccinelle 2016-07-22 12:13:39 +02:00
.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 modpost: dump missing namespaces into a single modules.nsdeps file 2019-11-11 20:10:01 +09:00
.mailmap MAINTAINERS: update my email address 2020-01-11 14:33:39 -08:00
COPYING COPYING: use the new text with points to the license files 2018-03-23 12:41:45 -06:00
CREDITS Linux 5.4-rc4 2019-10-29 04:43:29 -06:00
Kbuild kbuild: do not descend to ./Kbuild when cleaning 2019-08-21 21:03:58 +09:00
Kconfig docs: kbuild: convert docs to ReST and rename to *.rst 2019-06-14 14:21:21 -06:00
MAINTAINERS MAINTAINERS: correct entries for ISDN/mISDN section 2020-02-11 04:36:38 -08:00
Makefile Linux 5.5.3 2020-02-11 04:37:31 -08:00
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.