d3466ce4f4
[ Upstream commit b29a2acd36dd7a33c63f260df738fb96baa3d4f8 ]
Performance counters are defined to have width less than 64 bits. The
vPMU code maintains the counters in u64 variables but assumes the value
to fit within the defined width. However, for Intel non-full-width
counters (MSR_IA32_PERFCTRx) the value receieved from the guest is
truncated to 32 bits and then sign-extended to full 64 bits. If a
negative value is set, it's sign-extended to 64 bits, but then in
kvm_pmu_incr_counter() it's incremented, truncated, and compared to the
previous value for overflow detection.
That previous value is not truncated, so it always evaluates bigger than
the truncated new one, and a PMI is injected. If the PMI handler writes
a negative counter value itself, the vCPU never quits the PMI loop.
Turns out that Linux PMI handler actually does write the counter with
the value just read with RDPMC, so when no full-width support is exposed
via MSR_IA32_PERF_CAPABILITIES, and the guest initializes the counter to
a negative value, it locks up.
This has been observed in the field, for example, when the guest configures
atop to use perfevents and runs two instances of it simultaneously.
To address the problem, maintain the invariant that the counter value
always fits in the defined bit width, by truncating the received value
in the respective set_msr methods. For better readability, factor the
out into a helper function, pmc_write_counter(), shared by vmx and svm
parts.
Fixes: 9cd803d496e7 ("KVM: x86: Update vPMCs when retiring instructions")
Cc: stable@vger.kernel.org
Signed-off-by: Roman Kagan <rkagan@amazon.de>
Link: https://lore.kernel.org/all/20230504120042.785651-1-rkagan@amazon.de
Tested-by: Like Xu <likexu@tencent.com>
[sean: tweak changelog, s/set/write in the helper]
Signed-off-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
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.