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63279eeb7f
The performance monitoring unit (PMU) registers are saved on guest
exit when the guest has set the pmcregs_in_use flag in its lppaca, if
it exists, or unconditionally if it doesn't. If a nested guest is
being run then the hypervisor doesn't, and in most cases can't, know
if the PMU registers are in use since it doesn't know the location of
the lppaca for the nested guest, although it may have one for its
immediate guest. This results in the values of these registers being
lost across nested guest entry and exit in the case where the nested
guest was making use of the performance monitoring facility while it's
nested guest hypervisor wasn't.
Further more the hypervisor could interrupt a guest hypervisor between
when it has loaded up the PMU registers and it calling H_ENTER_NESTED
or between returning from the nested guest to the guest hypervisor and
the guest hypervisor reading the PMU registers, in
kvmhv_p9_guest_entry(). This means that it isn't sufficient to just
save the PMU registers when entering or exiting a nested guest, but
that it is necessary to always save the PMU registers whenever a guest
is capable of running nested guests to ensure the register values
aren't lost in the context switch.
Ensure the PMU register values are preserved by always saving their
value into the vcpu struct when a guest is capable of running nested
guests.
This should have minimal performance impact however any impact can be
avoided by booting a guest with "-machine pseries,cap-nested-hv=false"
on the qemu commandline.
Fixes:
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| arch | ||
| block | ||
| certs | ||
| crypto | ||
| Documentation | ||
| drivers | ||
| fs | ||
| include | ||
| init | ||
| ipc | ||
| kernel | ||
| lib | ||
| LICENSES | ||
| mm | ||
| net | ||
| samples | ||
| scripts | ||
| security | ||
| sound | ||
| tools | ||
| usr | ||
| virt | ||
| .clang-format | ||
| .cocciconfig | ||
| .get_maintainer.ignore | ||
| .gitattributes | ||
| .gitignore | ||
| .mailmap | ||
| COPYING | ||
| CREDITS | ||
| Kbuild | ||
| Kconfig | ||
| MAINTAINERS | ||
| Makefile | ||
| 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.