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Sean Christopherson 7649412af3 KVM: x86: Load guest/host PKRU outside of the fastpath run loop 
Move KVM's swapping of PKRU outside of the fastpath loop, as there is no
KVM code anywhere in the fastpath that accesses guest/userspace memory,
i.e. that can consume protection keys.

As documented by commit 1be0e61c1f ("KVM, pkeys: save/restore PKRU when
guest/host switches"), KVM just needs to ensure the host's PKRU is loaded
when KVM (or the kernel at-large) may access userspace memory.  And at the
time of commit 1be0e61c1f, KVM didn't have a fastpath, and PKU was
strictly contained to VMX, i.e. there was no reason to swap PKRU outside
of vmx_vcpu_run().

Over time, the "need" to swap PKRU close to VM-Enter was likely falsely
solidified by the association with XFEATUREs in commit 37486135d3
("KVM: x86: Fix pkru save/restore when guest CR4.PKE=0, move it to x86.c"),
and XFEATURE swapping was in turn moved close to VM-Enter/VM-Exit as a
KVM hack-a-fix ution for an #MC handler bug by commit 1811d979c7
("x86/kvm: move kvm_load/put_guest_xcr0 into atomic context").

Deferring the PKRU loads shaves ~40 cycles off the fastpath for Intel,
and ~60 cycles for AMD.  E.g. using INVD in KVM-Unit-Test's vmexit.c,
with extra hacks to enable CR4.PKE and PKRU=(-1u & ~0x3), latency numbers
for AMD Turin go from ~1560 => ~1500, and for Intel Emerald Rapids, go
from ~810 => ~770.

Reviewed-by: Rick Edgecombe <rick.p.edgecombe@intel.com>
Reviewed-by: Jon Kohler <jon@nutanix.com>
Link: https://patch.msgid.link/20251118222328.2265758-5-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>
History 2025-11-19 05:41:11 -08:00
arch KVM: x86: Load guest/host PKRU outside of the fastpath run loop 2025-11-19 05:41:11 -08:00
block block-6.18-20251016 2025-10-17 08:31:26 -07:00
certs sign-file,extract-cert: use pkcs11 provider for OPENSSL MAJOR >= 3 2024-09-20 19:52:48 +03:00
crypto This push contains the following changes: 2025-10-10 08:56:16 -07:00
Documentation Rust 'rustfmt' cleanup 2025-10-18 10:05:13 -10:00
drivers Hi, 2025-10-18 08:38:28 -10:00
fs Description for this pull request: 2025-10-18 07:23:59 -10:00
include hid-for-linus-2025101701 2025-10-18 08:18:18 -10:00
init printk changes for 6.18 2025-10-04 11:13:11 -07:00
io_uring io_uring/rw: check for NULL io_br_sel when putting a buffer 2025-10-15 13:38:53 -06:00
ipc namespace-6.18-rc1 2025-09-29 11:20:29 -07:00
kernel - Make sure the check for lost pelt idle time is done unconditionally to 2025-10-19 04:59:43 -10:00
lib lib/test_kho: use kho_preserve_vmalloc instead of storing addresses in fdt 2025-10-07 13:48:56 -07:00
LICENSES LICENSES: Replace the obsolete address of the FSF in the GFDL-1.2 2025-07-24 11:15:39 +02:00
mm slab: reset slab->obj_ext when freeing and it is OBJEXTS_ALLOC_FAIL 2025-10-16 15:16:45 +02:00
net bpf-fixes 2025-10-18 08:00:43 -10:00
rust rust: bitmap: fix formatting 2025-10-17 13:02:22 +02:00
samples Char/Misc/IIO/Binder changes for 6.18-rc1 2025-10-04 16:26:32 -07:00
scripts Kbuild fixes for 6.18 #1 2025-10-11 15:47:12 -07:00
security integrity-v6.18 2025-10-05 10:48:33 -07:00
sound ALSA: hda/realtek: Fix mute led for HP Omen 17-cb0xxx 2025-10-17 16:37:21 +02:00
tools hid-for-linus-2025101701 2025-10-18 08:18:18 -10:00
usr gen_init_cpio: Ignore fsync() returning EINVAL on pipes 2025-10-07 09:53:05 -07:00
virt KVM x86 fixes for 6.18: 2025-10-18 10:25:43 +02:00
.clang-format memblock: drop for_each_free_mem_pfn_range_in_zone_from() 2025-09-14 08:49:03 +03:00
.clippy.toml rust: clean Rust 1.88.0's warning about clippy::disallowed_macros configuration 2025-05-07 00:11:47 +02:00
.cocciconfig scripts: add Linux .cocciconfig for coccinelle 2016-07-22 12:13:39 +02:00
.editorconfig .editorconfig: remove trim_trailing_whitespace option 2024-06-13 16:47:52 +02:00
.get_maintainer.ignore MAINTAINERS: remove Alyssa Rosenzweig 2025-09-18 21:17:31 +02:00
.gitattributes .gitattributes: set diff driver for Rust source code files 2023-05-31 17:48:25 +02:00
.gitignore .gitignore: ignore compile_commands.json globally 2025-08-12 15:53:55 -07:00
.mailmap Including fixes from CAN 2025-10-16 09:41:21 -07:00
.pylintrc tools: docs: parse-headers.py: move it from sphinx dir 2025-08-29 15:54:42 -06:00
.rustfmt.toml rust: add .rustfmt.toml 2022-09-28 09:02:20 +02:00
COPYING COPYING: state that all contributions really are covered by this file 2020-02-10 13:32:20 -08:00
CREDITS USB/Thunderbolt changes for 6.18-rc1 2025-10-04 16:07:08 -07:00
Kbuild sched: Make migrate_{en,dis}able() inline 2025-09-25 09:57:16 +02:00
Kconfig io_uring: Rename KConfig to Kconfig 2025-02-19 14:53:27 -07:00
MAINTAINERS Including fixes from CAN 2025-10-16 09:41:21 -07:00
Makefile Linux 6.18-rc2 2025-10-19 15:19:16 -10:00
README README: Fix spelling 2024-03-18 03:36:32 -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 reStructuredText 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.