Re: [PATCH v2 06/24] kvm: arm64: Move hyp-init params to a per-CPU struct

[Marc Zyngier <maz@kernel.org>]

On Mon, 16 Nov 2020 20:43:00 +0000,
David Brazdil <dbrazdil@google.com> wrote:
> 
> Once we start initializing KVM on newly booted cores before the rest of
> the kernel, parameters to __do_hyp_init will need to be provided by EL2
> rather than EL1. At that point it will not be possible to pass its four
> arguments directly because PSCI_CPU_ON only supports one context
> argument.
> 
> Refactor __do_hyp_init to accept its parameters in a struct. This
> prepares the code for KVM booting cores as well as removes any limits on
> the number of __do_hyp_init arguments.
> 
> Signed-off-by: David Brazdil <dbrazdil@google.com>
> ---
>  arch/arm64/include/asm/kvm_asm.h   |  7 +++++++
>  arch/arm64/include/asm/kvm_hyp.h   |  4 ++++
>  arch/arm64/kernel/asm-offsets.c    |  4 ++++
>  arch/arm64/kvm/arm.c               | 26 ++++++++++++++------------
>  arch/arm64/kvm/hyp/nvhe/hyp-init.S | 21 ++++++++++-----------
>  arch/arm64/kvm/hyp/nvhe/hyp-main.c |  2 ++
>  6 files changed, 41 insertions(+), 23 deletions(-)
> 
> diff --git a/arch/arm64/include/asm/kvm_asm.h b/arch/arm64/include/asm/kvm_asm.h
> index 54387ccd1ab2..01904e88cead 100644
> --- a/arch/arm64/include/asm/kvm_asm.h
> +++ b/arch/arm64/include/asm/kvm_asm.h
> @@ -150,6 +150,13 @@ extern void *__vhe_undefined_symbol;
>  
>  #endif
>  
> +struct kvm_nvhe_init_params {
> +	unsigned long tpidr_el2;
> +	unsigned long vector_hyp_va;
> +	unsigned long stack_hyp_va;
> +	phys_addr_t pgd_pa;
> +};
> +
>  /* Translate a kernel address @ptr into its equivalent linear mapping */
>  #define kvm_ksym_ref(ptr)						\
>  	({								\
> diff --git a/arch/arm64/include/asm/kvm_hyp.h b/arch/arm64/include/asm/kvm_hyp.h
> index 6b664de5ec1f..a3289071f3d8 100644
> --- a/arch/arm64/include/asm/kvm_hyp.h
> +++ b/arch/arm64/include/asm/kvm_hyp.h
> @@ -15,6 +15,10 @@
>  DECLARE_PER_CPU(struct kvm_cpu_context, kvm_hyp_ctxt);
>  DECLARE_PER_CPU(unsigned long, kvm_hyp_vector);
>  
> +#ifdef __KVM_NVHE_HYPERVISOR__
> +DECLARE_PER_CPU(struct kvm_nvhe_init_params, kvm_init_params);
> +#endif

I'm not sure we should bother with this #ifdefery. Having the
declaration present at all times doesn't really hurt, since it is only
defined in the HYP code. Cutting down on the conditionals would
certainly help readability.

> +
>  #define read_sysreg_elx(r,nvh,vh)					\
>  	({								\
>  		u64 reg;						\
> diff --git a/arch/arm64/kernel/asm-offsets.c b/arch/arm64/kernel/asm-offsets.c
> index 7d32fc959b1a..4435ad8be938 100644
> --- a/arch/arm64/kernel/asm-offsets.c
> +++ b/arch/arm64/kernel/asm-offsets.c
> @@ -110,6 +110,10 @@ int main(void)
>    DEFINE(CPU_APGAKEYLO_EL1,	offsetof(struct kvm_cpu_context, sys_regs[APGAKEYLO_EL1]));
>    DEFINE(HOST_CONTEXT_VCPU,	offsetof(struct kvm_cpu_context, __hyp_running_vcpu));
>    DEFINE(HOST_DATA_CONTEXT,	offsetof(struct kvm_host_data, host_ctxt));
> +  DEFINE(NVHE_INIT_TPIDR_EL2,	offsetof(struct kvm_nvhe_init_params, tpidr_el2));
> +  DEFINE(NVHE_INIT_VECTOR_HYP_VA,	offsetof(struct kvm_nvhe_init_params, vector_hyp_va));
> +  DEFINE(NVHE_INIT_STACK_HYP_VA,	offsetof(struct kvm_nvhe_init_params, stack_hyp_va));
> +  DEFINE(NVHE_INIT_PGD_PA,	offsetof(struct kvm_nvhe_init_params, pgd_pa));
>  #endif
>  #ifdef CONFIG_CPU_PM
>    DEFINE(CPU_CTX_SP,		offsetof(struct cpu_suspend_ctx, sp));
> diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c
> index c0ffb019ca8b..4838556920fb 100644
> --- a/arch/arm64/kvm/arm.c
> +++ b/arch/arm64/kvm/arm.c
> @@ -50,6 +50,7 @@ DECLARE_KVM_HYP_PER_CPU(unsigned long, kvm_hyp_vector);
>  
>  static DEFINE_PER_CPU(unsigned long, kvm_arm_hyp_stack_page);
>  unsigned long kvm_arm_hyp_percpu_base[NR_CPUS];
> +DECLARE_KVM_NVHE_PER_CPU(struct kvm_nvhe_init_params, kvm_init_params);
>  
>  /* The VMID used in the VTTBR */
>  static atomic64_t kvm_vmid_gen = ATOMIC64_INIT(1);
> @@ -1347,10 +1348,7 @@ static int kvm_map_vectors(void)
>  
>  static void cpu_init_hyp_mode(void)
>  {
> -	phys_addr_t pgd_ptr;
> -	unsigned long hyp_stack_ptr;
> -	unsigned long vector_ptr;
> -	unsigned long tpidr_el2;
> +	struct kvm_nvhe_init_params *params = this_cpu_ptr_nvhe_sym(kvm_init_params);
>  	struct arm_smccc_res res;
>  
>  	/* Switch from the HYP stub to our own HYP init vector */
> @@ -1361,13 +1359,18 @@ static void cpu_init_hyp_mode(void)
>  	 * kernel's mapping to the linear mapping, and store it in tpidr_el2
>  	 * so that we can use adr_l to access per-cpu variables in EL2.
>  	 */
> -	tpidr_el2 = (unsigned long)this_cpu_ptr_nvhe_sym(__per_cpu_start) -
> -		    (unsigned long)kvm_ksym_ref(CHOOSE_NVHE_SYM(__per_cpu_start));
> +	params->tpidr_el2 = (unsigned long)this_cpu_ptr_nvhe_sym(__per_cpu_start) -
> +			    (unsigned long)kvm_ksym_ref(CHOOSE_NVHE_SYM(__per_cpu_start));
>  
> -	pgd_ptr = kvm_mmu_get_httbr();
> -	hyp_stack_ptr = __this_cpu_read(kvm_arm_hyp_stack_page) + PAGE_SIZE;
> -	hyp_stack_ptr = kern_hyp_va(hyp_stack_ptr);
> -	vector_ptr = (unsigned long)kern_hyp_va(kvm_ksym_ref(__kvm_hyp_host_vector));
> +	params->vector_hyp_va = (unsigned long)kern_hyp_va(kvm_ksym_ref(__kvm_hyp_host_vector));
> +	params->stack_hyp_va = kern_hyp_va(__this_cpu_read(kvm_arm_hyp_stack_page) + PAGE_SIZE);
> +	params->pgd_pa = kvm_mmu_get_httbr();

Note to self: rename this to kvm_mmu_get_hyp_pgd() (another AArch32-ism).

> +
> +	/*
> +	 * Flush the init params from the data cache because the struct will
> +	 * be read while the MMU is off.
> +	 */
> +	__flush_dcache_area(params, sizeof(*params));

nit: please use kvm_flush_dcache_to_poc(), as it clearly indicates to
which point we are flushing.

Thanks,

	M.

-- 
Without deviation from the norm, progress is not possible.

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