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Xiaoyao Li ccb2280ec2 x86/kvm: Use separate percpu variable to track the enabling of asyncpf 
Refer to commit fd10cde929 ("KVM paravirt: Add async PF initialization
to PV guest") and commit 344d9588a9 ("KVM: Add PV MSR to enable
asynchronous page faults delivery"). It turns out that at the time when
asyncpf was introduced, the purpose was defining the shared PV data 'struct
kvm_vcpu_pv_apf_data' with the size of 64 bytes. However, it made a mistake
and defined the size to 68 bytes, which failed to make fit in a cache line
and made the code inconsistent with the documentation.

Below justification quoted from Sean[*]

  KVM (the host side) has *never* read kvm_vcpu_pv_apf_data.enabled, and
  the documentation clearly states that enabling is based solely on the
  bit in the synthetic MSR.

  So rather than update the documentation, fix the goof by removing the
  enabled filed and use the separate percpu variable instread.
  KVM-as-a-host obviously doesn't enforce anything or consume the size,
  and changing the header will only affect guests that are rebuilt against
  the new header, so there's no chance of ABI breakage between KVM and its
  guests. The only possible breakage is if some other hypervisor is
  emulating KVM's async #PF (LOL) and relies on the guest to set
  kvm_vcpu_pv_apf_data.enabled. But (a) I highly doubt such a hypervisor
  exists, (b) that would arguably be a violation of KVM's "spec", and
  (c) the worst case scenario is that the guest would simply lose async
  #PF functionality.

[*] https://lore.kernel.org/all/ZS7ERnnRqs8Fl0ZF@google.com/T/#u

Suggested-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Xiaoyao Li <xiaoyao.li@intel.com>
Link: https://lore.kernel.org/r/20231025055914.1201792-2-xiaoyao.li@intel.com
[sean: use true/false instead of 1/0 for booleans]
Signed-off-by: Sean Christopherson <seanjc@google.com>
History 2024-02-06 10:58:56 -08:00
arch x86/kvm: Use separate percpu variable to track the enabling of asyncpf 2024-02-06 10:58:56 -08:00
block block: Fix WARNING in _copy_from_iter 2024-01-23 08:56:55 -07:00
certs This update includes the following changes: 2023-11-02 16:15:30 -10:00
crypto crypto: scomp - fix req->dst buffer overflow 2023-12-29 11:25:56 +08:00
Documentation x86/kvm: Use separate percpu variable to track the enabling of asyncpf 2024-02-06 10:58:56 -08:00
drivers cxl fixes for 6.8-rc2 2024-01-28 13:55:56 -08:00
fs Bug fixes for 6.8-rc2: 2024-01-27 09:17:01 -08:00
include - Make sure 32-bit syscall registers are properly sign-extended 2024-01-28 09:45:11 -08:00
init init: Kconfig: Disable -Wstringop-overflow for GCC-11 2024-01-21 17:45:31 -06:00
io_uring io_uring: enable audit and restrict cred override for IORING_OP_FIXED_FD_INSTALL 2024-01-23 15:25:14 -07:00
ipc shm: Slim down dependencies 2023-12-20 19:26:31 -05:00
kernel - Prevent an inconsistent futex operation leading to stale state 2024-01-28 10:38:16 -08:00
lib RISC-V Patches for the 6.8 Merge Window, Part 4 2024-01-20 11:06:04 -08:00
LICENSES LICENSES: Add the copyleft-next-0.3.1 license 2022-11-08 15:44:01 +01:00
mm memblock: fix crash when reserved memory is not added to memory 2024-01-28 09:41:39 -08:00
net Including fixes from bpf, netfilter and WiFi. 2024-01-25 10:58:35 -08:00
rust Rust changes for v6.8 2024-01-11 13:05:41 -08:00
samples samples/cgroup: add .gitignore file for generated samples 2024-01-24 11:52:40 -08:00
scripts Makefile: Enable -Wstringop-overflow globally 2024-01-21 17:45:31 -06:00
security integrity-6.8-rc1 2024-01-24 16:51:59 -08:00
sound sound fixes for 6.8-rc1 2024-01-19 12:30:29 -08:00
tools cxl fixes for 6.8-rc2 2024-01-28 13:55:56 -08:00
usr Kbuild updates for v6.8 2024-01-18 17:57:07 -08:00
virt Generic: 2024-01-17 13:03:37 -08:00
.clang-format clang-format: Update with v6.7-rc4's for_each macro list 2023-12-08 23:54:38 +01:00
.cocciconfig scripts: add Linux .cocciconfig for coccinelle 2016-07-22 12:13:39 +02:00
.editorconfig Add .editorconfig file for basic formatting 2023-12-28 16:22:47 +09:00
.get_maintainer.ignore get_maintainer: add Alan to .get_maintainer.ignore 2022-08-20 15:17:44 -07:00
.gitattributes .gitattributes: set diff driver for Rust source code files 2023-05-31 17:48:25 +02:00
.gitignore Add .editorconfig file for basic formatting 2023-12-28 16:22:47 +09:00
.mailmap Char/Misc and other Driver changes for 6.8-rc1 2024-01-17 16:47:17 -08:00
.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 Including fixes from bpf and netfilter. 2024-01-18 17:33:50 -08:00
Kbuild Kbuild updates for v6.1 2022-10-10 12:00:45 -07:00
Kconfig kbuild: ensure full rebuild when the compiler is updated 2020-05-12 13:28:33 +09:00
MAINTAINERS platform-drivers-x86 for v6.8-2 2024-01-27 09:48:55 -08:00
Makefile Linux 6.8-rc2 2024-01-28 17:01:12 -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.