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Gabriel Krisman Bertazi a98ad3adf6 arm64: Avoid repeated AA64MMFR1_EL1 register read on pagefault path 
[ Upstream commit a89c6bcdac ]

Accessing AA64MMFR1_EL1 is expensive in KVM guests, since it is emulated
in the hypervisor.  In fact, ARM documentation mentions some feature
registers are not supposed to be accessed frequently by the OS, and
therefore should be emulated for guests [1].

Commit 0388f9c743 ("arm64: mm: Implement
arch_wants_old_prefaulted_pte()") introduced a read of this register in
the page fault path.  But, even when the feature of setting faultaround
pages with the old flag is disabled for a given cpu, we are still paying
the cost of checking the register on every pagefault. This results in an
explosion of vmexit events in KVM guests, which directly impacts the
performance of virtualized workloads.  For instance, running kernbench
yields a 15% increase in system time solely due to the increased vmexit
cycles.

This patch avoids the extra cost by using the sanitized cached value.
It should be safe to do so, since this register mustn't change for a
given cpu.

[1] https://developer.arm.com/-/media/Arm%20Developer%20Community/PDF/Learn%20the%20Architecture/Armv8-A%20virtualization.pdf?revision=a765a7df-1a00-434d-b241-357bfda2dd31

Signed-off-by: Gabriel Krisman Bertazi <krisman@suse.de>
Acked-by: Will Deacon <will@kernel.org>
Reviewed-by: Anshuman Khandual <anshuman.khandual@arm.com>
Link: https://lore.kernel.org/r/20230109151955.8292-1-krisman@suse.de
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
History 2023-10-10 21:59:05 +02:00
arch arm64: Avoid repeated AA64MMFR1_EL1 register read on pagefault path 2023-10-10 21:59:05 +02:00
block block: don't add or resize partition on the disk with GENHD_FL_NO_PART 2023-09-19 12:23:03 +02:00
certs certs/blacklist_hashes.c: fix const confusion in certs blacklist 2022-06-22 14:22:01 +02:00
crypto crypto: lrw,xts - Replace strlcpy with strscpy 2023-09-23 11:09:55 +02:00
Documentation perf/smmuv3: Enable HiSilicon Erratum 162001900 quirk for HIP08/09 2023-09-23 11:09:55 +02:00
drivers spi: zynqmp-gqspi: fix clock imbalance on probe failure 2023-10-10 21:59:04 +02:00
fs NFSv4: Fix a state manager thread deadlock regression 2023-10-10 21:59:04 +02:00
include netfilter: nf_tables: fix kdoc warnings after gc rework 2023-10-06 13:18:24 +02:00
init x86/mm: Initialize text poking earlier 2023-08-08 19:58:33 +02:00
io_uring io_uring/fs: remove sqe->rw_flags checking from LINKAT 2023-10-06 13:18:22 +02:00
ipc ipc/sem: Fix dangling sem_array access in semtimedop race 2022-12-08 11:28:45 +01:00
kernel ring-buffer: Fix bytes info in per_cpu buffer stats 2023-10-10 21:59:05 +02:00
lib kobject: Add sanity check for kset->kobj.ktype in kset_register() 2023-09-23 11:09:59 +02:00
LICENSES LICENSES/dual/CC-BY-4.0: Git rid of "smart quotes" 2021-07-15 06:31:24 -06:00
mm mm/vmalloc: add a safer version of find_vm_area() for debug 2023-09-19 12:22:50 +02:00
net netfilter: nf_tables: fix kdoc warnings after gc rework 2023-10-06 13:18:24 +02:00
samples samples/hw_breakpoint: fix building without module unloading 2023-09-23 11:10:01 +02:00
scripts kconfig: fix possible buffer overflow 2023-09-19 12:22:56 +02:00
security Smack:- Use overlay inode label in smack_inode_copy_up() 2023-10-06 13:18:20 +02:00
sound ASoC: tegra: Fix redundant PLLA and PLLA_OUT0 updates 2023-10-10 21:59:04 +02:00
tools bpf: Fix BTF_ID symbol generation collision in tools/ 2023-10-06 13:18:23 +02:00
usr usr/include/Makefile: add linux/nfc.h to the compile-test coverage 2022-02-01 17:27:15 +01:00
virt KVM: Grab a reference to KVM for VM and vCPU stats file descriptors 2023-08-03 10:22:40 +02:00
.clang-format clang-format: Update with the latest for_each macro list 2021-05-12 23:32:39 +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 .gitignore: ignore only top-level modules.builtin 2021-05-02 00:43:35 +09:00
.mailmap mailmap: add Andrej Shadura 2021-10-18 20:22:03 -10:00
COPYING COPYING: state that all contributions really are covered by this file 2020-02-10 13:32:20 -08:00
CREDITS MAINTAINERS: Move Daniel Drake to credits 2021-09-21 08:34:58 +03:00
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 iio: stx104: Move to addac subdirectory 2023-08-26 14:23:27 +02:00
Makefile Linux 5.15.134 2023-10-06 13:18:24 +02:00
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.