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Dave Martin d8ad71fa38 arm64: fpsimd: Fix TIF_FOREIGN_FPSTATE after invalidating cpu regs 
fpsimd_last_state.st is set to NULL as a way of indicating that
current's FPSIMD registers are no longer loaded in the cpu.  In
particular, this is done when the kernel temporarily uses or
clobbers the FPSIMD registers for its own purposes, as in CPU PM or
kernel-mode NEON, resulting in them being populated with garbage
data not belonging to a task.

Commit 17eed27b02 ("arm64/sve: KVM: Prevent guests from using
SVE") factors this operation out as a new helper
fpsimd_flush_cpu_state() to make it clearer what is being done
here, and on SVE systems this helper is now used, via
kvm_fpsimd_flush_cpu_state(), to invalidate the registers after KVM
has run a vcpu.  The reason for this is that KVM does not yet
understand how to restore the full host SVE registers itself after
loading the guest FPSIMD context into them.

This exposes a particular problem: if fpsimd_last_state.st is set
to NULL without also setting TIF_FOREIGN_FPSTATE, the kernel may
continue to think that current's FPSIMD registers are live even
though they have actually been clobbered.

Prior to the aforementioned commit, the only path where
fpsimd_last_state.st is set to NULL without setting
TIF_FOREIGN_FPSTATE is when kernel_neon_begin() is called by a
kernel thread (where current->mm can be NULL).  This does not
matter, because the only harm is that at context-switch time
fpsimd_thread_switch() may unnecessarily save the FPSIMD registers
back to current's thread_struct (even though kernel threads are not
considered to have any FPSIMD context of their own and the
registers will never be reloaded).

Note that although CPU_PM_ENTER lacks the TIF_FOREIGN_FPSTATE
setting, every CPU passing through that path must subsequently pass
through CPU_PM_EXIT before it can re-enter the kernel proper.
CPU_PM_EXIT sets the flag.

The sve_flush_cpu_state() function added by commit 17eed27b02
also lacks the proper maintenance of TIF_FOREIGN_FPSTATE.  This may
cause the bits of a host task's SVE registers that do not alias the
FPSIMD register file to spontaneously appear zeroed if a KVM vcpu
runs in the same task in the meantime.  Although this effect is
hidden by the fact that the non-FPSIMD bits of the SVE registers
are zeroed by a syscall anyway, it is doubtless a bad idea to rely
on these different code paths interacting correctly under future
maintenance.

This patch makes TIF_FOREIGN_FPSTATE an unconditional side-effect
of fpsimd_flush_cpu_state(), and removes the set_thread_flag()
calls that become redundant as a result.  This ensures that
TIF_FOREIGN_FPSTATE cannot remain clear if the FPSIMD state in the
FPSIMD registers is invalid.

Signed-off-by: Dave Martin <Dave.Martin@arm.com>
Reviewed-by: Christoffer Dall <christoffer.dall@arm.com>
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will.deacon@arm.com>
Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
 		2018-05-25 12:27:53 +01:00
Documentation media fixes for v4.17-rc4 2018-05-04 05:38:51 -10:00
LICENSES LICENSES: Add MPL-1.1 license 2018-01-06 10:59:44 -07:00
arch arm64: fpsimd: Fix TIF_FOREIGN_FPSTATE after invalidating cpu regs 2018-05-25 12:27:53 +01:00
block blk-mq: fix sysfs inflight counter 2018-04-26 09:02:01 -06:00
certs certs/blacklist_nohashes.c: fix const confusion in certs blacklist 2018-02-21 15:35:43 -08:00
crypto crypto: drbg - set freed buffers to NULL 2018-04-21 00:57:00 +08:00
drivers IOMMU Fixes for Linux v4.17-rc4 2018-05-06 05:42:24 -10:00
firmware kbuild: remove all dummy assignments to obj- 2017-11-18 11:46:06 +09:00
fs First pull request for 4.17-rc 2018-05-04 20:51:10 -10:00
include KVM fixes for v4.17-rc4 2018-05-06 05:46:29 -10:00
init Merge branch 'x86-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 2018-04-15 16:12:35 -07:00
ipc ipc/shm: fix use-after-free of shm file via remap_file_pages() 2018-04-13 17:10:27 -07:00
kernel Merge branch 'timers-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 2018-05-06 05:35:23 -10:00
lib swiotlb: fix inversed DMA_ATTR_NO_WARN test 2018-05-02 14:48:55 +02:00
mm for-linus-20180504 2018-05-04 20:41:44 -10:00
net Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net 2018-05-03 18:57:03 -10:00
samples bpf: sockmap sample use clang flag, -target bpf 2018-04-23 23:42:21 +02:00
scripts Kbuild fixes for v4.17 2018-05-04 21:15:25 -10:00
security Merge branch 'userns-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/ebiederm/user-namespace 2018-04-24 17:58:51 -07:00
sound ALSA: pcm: Check PCM state at xfern compat ioctl 2018-05-02 08:54:54 +02:00
tools ACPI fix for 4.17-rc4 2018-05-04 05:43:33 -10:00
usr kbuild: rename built-in.o to built-in.a 2018-03-26 02:01:19 +09:00
virt KVM/arm fixes for 4.17, take #2 2018-05-05 23:05:31 +02:00
.clang-format clang-format: add configuration file 2018-04-11 10:28:35 -07:00
.cocciconfig scripts: add Linux .cocciconfig for coccinelle 2016-07-22 12:13:39 +02:00
.get_maintainer.ignore
…
.gitattributes .gitattributes: set git diff driver for C source code files 2016-10-07 18:46:30 -07:00
.gitignore Kbuild updates for v4.17 (2nd) 2018-04-15 17:21:30 -07:00
.mailmap Merge candidates for 4.17 merge window 2018-04-06 17:35:43 -07:00
COPYING COPYING: use the new text with points to the license files 2018-03-23 12:41:45 -06:00
CREDITS MAINTAINERS/CREDITS: Drop METAG ARCHITECTURE 2018-03-05 16:34:24 +00:00
Kbuild Kbuild updates for v4.15 2017-11-17 17:45:29 -08:00
Kconfig License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
MAINTAINERS Kbuild fixes for v4.17 2018-05-04 21:15:25 -10:00
Makefile Linux 4.17-rc4 2018-05-06 16:57:38 -10:00
README Docs: Added a pointer to the formatted docs to README 2018-03-21 09:02:53 -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.
See Documentation/00-INDEX for a list of what is contained in each file.

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.