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263d6287da
When a VCPU is created, the kvm_vcpu struct is initialized to zero in
kvm_vm_ioctl_create_vcpu(). On VHE systems, the first time
vcpu.arch.mdcr_el2 is loaded on hardware is in vcpu_load(), before it is
set to a sensible value in kvm_arm_setup_debug() later in the run loop. The
result is that KVM executes for a short time with MDCR_EL2 set to zero.
This has several unintended consequences:
* Setting MDCR_EL2.HPMN to 0 is constrained unpredictable according to ARM
DDI 0487G.a, page D13-3820. The behavior specified by the architecture
in this case is for the PE to behave as if MDCR_EL2.HPMN is set to a
value less than or equal to PMCR_EL0.N, which means that an unknown
number of counters are now disabled by MDCR_EL2.HPME, which is zero.
* The host configuration for the other debug features controlled by
MDCR_EL2 is temporarily lost. This has been harmless so far, as Linux
doesn't use the other fields, but that might change in the future.
Let's avoid both issues by initializing the VCPU's mdcr_el2 field in
kvm_vcpu_vcpu_first_run_init(), thus making sure that the MDCR_EL2 register
has a consistent value after each vcpu_load().
Fixes:
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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.