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Sean Christopherson f91b4038b6 KVM: nVMX: Attempt to load PERF_GLOBAL_CTRL on nVMX xfer iff it exists 
[ Upstream commit 4496a6f9b4 ]

Attempt to load PERF_GLOBAL_CTRL during nested VM-Enter/VM-Exit if and
only if the MSR exists (according to the guest vCPU model).  KVM has very
misguided handling of VM_{ENTRY,EXIT}_LOAD_IA32_PERF_GLOBAL_CTRL and
attempts to force the nVMX MSR settings to match the vPMU model, i.e. to
hide/expose the control based on whether or not the MSR exists from the
guest's perspective.

KVM's modifications fail to handle the scenario where the vPMU is hidden
from the guest _after_ being exposed to the guest, e.g. by userspace
doing multiple KVM_SET_CPUID2 calls, which is allowed if done before any
KVM_RUN.  nested_vmx_pmu_refresh() is called if and only if there's a
recognized vPMU, i.e. KVM will leave the bits in the allow state and then
ultimately reject the MSR load and WARN.

KVM should not force the VMX MSRs in the first place.  KVM taking control
of the MSRs was a misguided attempt at mimicking what commit 5f76f6f5ff
("KVM: nVMX: Do not expose MPX VMX controls when guest MPX disabled",
2018-10-01) did for MPX.  However, the MPX commit was a workaround for
another KVM bug and not something that should be imitated (and it should
never been done in the first place).

In other words, KVM's ABI _should_ be that userspace has full control
over the MSRs, at which point triggering the WARN that loading the MSR
must not fail is trivial.

The intent of the WARN is still valid; KVM has consistency checks to
ensure that vmcs12->{guest,host}_ia32_perf_global_ctrl is valid.  The
problem is that '0' must be considered a valid value at all times, and so
the simple/obvious solution is to just not actually load the MSR when it
does not exist.  It is userspace's responsibility to provide a sane vCPU
model, i.e. KVM is well within its ABI and Intel's VMX architecture to
skip the loads if the MSR does not exist.

Fixes: 03a8871add ("KVM: nVMX: Expose load IA32_PERF_GLOBAL_CTRL VM-{Entry,Exit} control")
Cc: stable@vger.kernel.org
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20220722224409.1336532-5-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
History 2022-08-17 15:16:14 +02:00
arch KVM: nVMX: Attempt to load PERF_GLOBAL_CTRL on nVMX xfer iff it exists 2022-08-17 15:16:14 +02:00
block block: don't allow the same type rq_qos add more than once 2022-08-17 15:16:10 +02:00
certs certs: make system keyring depend on x509 parser 2022-07-24 12:53:55 -07:00
crypto crypto: blake2s - remove shash module 2022-08-17 15:16:07 +02:00
Documentation x86/bugs: Enable STIBP for IBPB mitigated RETBleed 2022-08-17 15:16:05 +02:00
drivers ACPI: CPPC: Do not prevent CPPC from working in the future 2022-08-17 15:16:13 +02:00
fs btrfs: join running log transaction when logging new name 2022-08-17 15:16:12 +02:00
include ACPI: CPPC: Do not prevent CPPC from working in the future 2022-08-17 15:16:13 +02:00
init stack: Declare {randomize_,}kstack_offset to fix Sparse warnings 2022-08-17 15:14:14 +02:00
io_uring io_uring: Don't require reinitable percpu_ref 2022-08-17 15:14:20 +02:00
ipc ipc: Free mq_sysctls if ipc namespace creation failed 2022-06-22 17:47:41 -05:00
kernel locking/csd_lock: Change csdlock_debug from early_param to __setup 2022-08-17 15:16:09 +02:00
lib crypto: blake2s - remove shash module 2022-08-17 15:16:07 +02:00
LICENSES LICENSES/LGPL-2.1: Add LGPL-2.1-or-later as valid identifiers 2021-12-16 14:33:10 +01:00
mm mm/mmap.c: fix missing call to vm_unacct_memory in mmap_region 2022-08-17 15:15:40 +02:00
net net/9p: Initialize the iounit field during fid creation 2022-08-17 15:16:09 +02:00
samples sample: bpf: xdp_router_ipv4: Allow the kernel to send arp requests 2022-08-17 15:14:25 +02:00
scripts scripts/faddr2line: Fix vmlinux detection on arm64 2022-08-17 15:16:01 +02:00
security selinux: Add boundary check in put_entry() 2022-08-17 15:14:06 +02:00
sound ASoC: mchp-spdifrx: disable end of block interrupt on failures 2022-08-17 15:15:57 +02:00
tools tools/thermal: Fix possible path truncations 2022-08-17 15:16:02 +02:00
usr Not a lot of material this cycle. Many singleton patches against various 2022-05-27 11:22:03 -07:00
virt KVM: Don't set Accessed/Dirty bits for ZERO_PAGE 2022-08-17 15:15:21 +02:00
.clang-format clang-format: Fix space after for_each macros 2022-05-20 19:27:16 +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 kbuild: split the second line of *.mod into *.usyms 2022-05-08 03:16:59 +09:00
.mailmap ARM: SoC fixes for 5.19, part 4 2022-07-27 09:43:07 -07:00
COPYING COPYING: state that all contributions really are covered by this file 2020-02-10 13:32:20 -08:00
CREDITS MAINTAINERS: mark ARM/PALM TREO SUPPORT orphan 2022-07-07 15:17:00 +02:00
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 io_uring: move to separate directory 2022-08-17 15:14:20 +02:00
Makefile io_uring: move to separate directory 2022-08-17 15:14:20 +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.