On 2020-12-28 10:49, Marc Zyngier wrote:
It recently came to light that there is a need to be able to override
some CPU features very early on, before the kernel is fully up and
running. The reasons for this range from specific feature support
(such as using Protected KVM on VHE HW, which is the main motivation
for this work) to errata workaround (a feature is broken on a CPU and
needs to be turned off, or rather not enabled).
This series tries to offer a limited framework for this kind of
problems, by allowing a set of options to be passed on the
command-line and altering the feature set that the cpufeature
subsystem exposes to the rest of the kernel. Note that this doesn't
change anything for code that directly uses the CPU ID registers.
The series completely changes the way a VHE-capable arm64 boots, by
*always* booting non-VHE first, and then upgrading to VHE when deemed
capable. Although this sounds scary, this is actually simple to
implement (and I wish I had though of it five years ago). The "upgrade
to VHE" path is then conditioned on the VHE feature not being disabled
from the command-line.
Said command-line parsing borrows a lot from the kaslr code, and
subsequently allows the "nokaslr" option to be moved to the new
infrastructure (though it all looks a bit... odd).
This has been tested on multiple VHE and non-VHE systems.
FWIW, I've just fixed a number of issues with this series, ranging
from compilation issues when CONFIG_RANDOMIZE_BASE is not set,
SPE setup bugs, and boot hangs when kaslr kicks in.
It all should be fixed now, and I have pushed an updated series
at [1], for those of you who really can't wait to try new stuff
while you could just ignore it all.
Thanks,
M.
[1]
https://git.kernel.org/pub/scm/linux/kernel/git/maz/arm-platforms.git/log/?h=hack/arm64-early-cpufeature
--
Jazz is not dead. It just smells funny...
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