| Message ID | 20201228104958.1848833-1-maz@kernel.org (mailing list archive) |
|---|---|
| Headers | show |
| Series | arm64: Early CPU feature override, and an application to VHE | expand |
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
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. Marc Zyngier (17): arm64: Fix labels in el2_setup macros arm64: Fix outdated TCR setup comment arm64: Turn the MMU-on sequence into a macro arm64: Provide an 'upgrade to VHE' stub hypercall arm64: Initialise as nVHE before switching to VHE arm64: Move VHE-specific SPE setup to mutate_to_vhe() arm64: Simplify init_el2_state to be non-VHE only arm64: Move SCTLR_EL1 initialisation to EL-agnostic code arm64: cpufeature: Add global feature override facility arm64: Extract early FDT mapping from kaslr_early_init() arm64: cpufeature: Add an early command-line cpufeature override facility arm64: Allow ID_AA64MMFR1_EL1.VH to be overridden from the command line arm64: Honor VHE being disabled from the command-line arm64: Add an aliasing facility for the idreg override arm64: Make kvm-arm.mode={nvhe,protected} an alias of id_aa64mmfr1.vh=0 KVM: arm64: Document HVC_VHE_RESTART stub hypercall arm64: Move "nokaslr" over to the early cpufeature infrastructure .../admin-guide/kernel-parameters.txt | 3 + Documentation/virt/kvm/arm/hyp-abi.rst | 9 + arch/arm64/include/asm/assembler.h | 17 ++ arch/arm64/include/asm/cpufeature.h | 5 + arch/arm64/include/asm/el2_setup.h | 60 +++---- arch/arm64/include/asm/setup.h | 11 ++ arch/arm64/include/asm/virt.h | 7 +- arch/arm64/kernel/Makefile | 2 +- arch/arm64/kernel/cpufeature.c | 32 +++- arch/arm64/kernel/head.S | 71 ++------ arch/arm64/kernel/hyp-stub.S | 117 ++++++++++++- arch/arm64/kernel/idreg-override.c | 161 ++++++++++++++++++ arch/arm64/kernel/kaslr.c | 44 +---- arch/arm64/kernel/setup.c | 15 ++ arch/arm64/kvm/arm.c | 3 + arch/arm64/kvm/hyp/nvhe/hyp-init.S | 2 +- arch/arm64/mm/proc.S | 16 +- 17 files changed, 415 insertions(+), 160 deletions(-) create mode 100644 arch/arm64/include/asm/setup.h create mode 100644 arch/arm64/kernel/idreg-override.c