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SubjectRe: [PATCH v1 13/24] kvm: arm64: Add CPU entry point in nVHE hyp
On 2020-11-09 11:32, David Brazdil wrote:
> When nVHE hyp starts interception host's PSCI CPU_ON SMCs, it will need
> to install KVM on the newly booted CPU before returning to the host.
> Add
> an entry point which expects the same kvm_nvhe_init_params struct as
> the
> __kvm_hyp_init HVC in the CPU_ON context argument (x0).
>
> The entry point initializes EL2 state with the same init_el2_state
> macro
> used by the kernel's entry point. It then initializes KVM using the
> same
> helper function used in the __kvm_hyp_init HVC.
>
> When done, the entry point branches to a function provided in the init
> params.
>
> Signed-off-by: David Brazdil <dbrazdil@google.com>
> ---
> arch/arm64/include/asm/kvm_asm.h | 1 +
> arch/arm64/kernel/asm-offsets.c | 1 +
> arch/arm64/kvm/hyp/nvhe/hyp-init.S | 30 ++++++++++++++++++++++++++++++
> 3 files changed, 32 insertions(+)
>
> diff --git a/arch/arm64/include/asm/kvm_asm.h
> b/arch/arm64/include/asm/kvm_asm.h
> index 893327d1e449..efb4872bb29f 100644
> --- a/arch/arm64/include/asm/kvm_asm.h
> +++ b/arch/arm64/include/asm/kvm_asm.h
> @@ -155,6 +155,7 @@ struct kvm_nvhe_init_params {
> unsigned long tpidr_el2;
> unsigned long hyp_stack_ptr;
> unsigned long vector_ptr;
> + unsigned long psci_cpu_entry_fn;
> };
>
> /* Translate a kernel address @ptr into its equivalent linear mapping
> */
> diff --git a/arch/arm64/kernel/asm-offsets.c
> b/arch/arm64/kernel/asm-offsets.c
> index 0cbb86135c7c..ffc84e68ad97 100644
> --- a/arch/arm64/kernel/asm-offsets.c
> +++ b/arch/arm64/kernel/asm-offsets.c
> @@ -114,6 +114,7 @@ int main(void)
> DEFINE(NVHE_INIT_TPIDR_EL2, offsetof(struct kvm_nvhe_init_params,
> tpidr_el2));
> DEFINE(NVHE_INIT_STACK_PTR, offsetof(struct kvm_nvhe_init_params,
> hyp_stack_ptr));
> DEFINE(NVHE_INIT_VECTOR_PTR, offsetof(struct kvm_nvhe_init_params,
> vector_ptr));
> + DEFINE(NVHE_INIT_PSCI_CPU_ENTRY_FN, offsetof(struct
> kvm_nvhe_init_params, psci_cpu_entry_fn));
> #endif
> #ifdef CONFIG_CPU_PM
> DEFINE(CPU_CTX_SP, offsetof(struct cpu_suspend_ctx, sp));
> diff --git a/arch/arm64/kvm/hyp/nvhe/hyp-init.S
> b/arch/arm64/kvm/hyp/nvhe/hyp-init.S
> index 1697d25756e9..f999a35b2c8c 100644
> --- a/arch/arm64/kvm/hyp/nvhe/hyp-init.S
> +++ b/arch/arm64/kvm/hyp/nvhe/hyp-init.S
> @@ -6,6 +6,7 @@
>
> #include <linux/arm-smccc.h>
> #include <linux/linkage.h>
> +#include <linux/irqchip/arm-gic-v3.h>

This should probably be included from the file that provides
init_el2_state.

>
> #include <asm/alternative.h>
> #include <asm/assembler.h>
> @@ -159,6 +160,35 @@ alternative_else_nop_endif
> ret
> SYM_CODE_END(___kvm_hyp_init)
>
> +SYM_CODE_START(__kvm_hyp_cpu_entry)
> + msr SPsel, #1 // We want to use SP_EL{1,2}
> +
> + /*
> + * Check that the core was booted in EL2. Loop indefinitely if not
> + * because it cannot be safely given to the host without installing
> KVM.
> + */
> + mrs x1, CurrentEL
> + cmp x1, #CurrentEL_EL2
> + b.ne .

This is a bit brutal. Consider using a WFE/WFI loop as we have in other
places already (see __secondary_too_slow for example).

> +
> + /* Initialize EL2 CPU state to sane values. */
> + mov x29, x0
> + init_el2_state nvhe
> + mov x0, x29
> +
> + /*
> + * Load hyp VA of C entry function. Must do so before switching on
> the
> + * MMU because the struct pointer is PA and not identity-mapped in
> hyp.
> + */
> + ldr x29, [x0, #NVHE_INIT_PSCI_CPU_ENTRY_FN]
> +
> + /* Enable MMU, set vectors and stack. */
> + bl ___kvm_hyp_init
> +
> + /* Leave idmap. */
> + br x29

To a point I made against an earlier patch: psci_cpu_entry_fn seems to
be a HYP
VA, and really needs to be documented as such, because this is pretty
hard to
follow otherwise.

> +SYM_CODE_END(__kvm_hyp_cpu_entry)
> +
> SYM_CODE_START(__kvm_handle_stub_hvc)
> cmp x0, #HVC_SOFT_RESTART
> b.ne 1f

Thanks,

M.
--
Jazz is not dead. It just smells funny...

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