Subject: Re: [PATCH v2 12/24] kvm: arm64: Bootstrap PSCI SMC handler in nVHE EL2

From: Marc Zyngier <[email-masked]>
Date: Mon, 23 Nov 2020 17:55:21 +0000

On Mon, 16 Nov 2020 20:43:06 +0000,
David Brazdil <[email-masked]> wrote:
> 
> Add a handler of PSCI SMCs in nVHE hyp code. The handler is initialized
> with the version used by the host's PSCI driver and the function IDs it
> was configured with. If the SMC function ID matches one of the
> configured PSCI calls (for v0.1) or falls into the PSCI function ID
> range (for v0.2+), the SMC is handled by the PSCI handler. For now, all
> SMCs return PSCI_RET_NOT_SUPPORTED.
> 
> Signed-off-by: David Brazdil <[email-masked]>
> ---
>  arch/arm64/include/asm/kvm_hyp.h     |   4 ++
>  arch/arm64/kvm/arm.c                 |  14 ++++
>  arch/arm64/kvm/hyp/nvhe/Makefile     |   2 +-
>  arch/arm64/kvm/hyp/nvhe/hyp-main.c   |   6 +-
>  arch/arm64/kvm/hyp/nvhe/psci-relay.c | 104 +++++++++++++++++++++++++++
>  5 files changed, 128 insertions(+), 2 deletions(-)
>  create mode 100644 arch/arm64/kvm/hyp/nvhe/psci-relay.c
> 
> diff --git a/arch/arm64/include/asm/kvm_hyp.h b/arch/arm64/include/asm/kvm_hyp.h
> index a3289071f3d8..95a2bbbcc7e1 100644
> --- a/arch/arm64/include/asm/kvm_hyp.h
> +++ b/arch/arm64/include/asm/kvm_hyp.h
> @@ -96,6 +96,10 @@ void deactivate_traps_vhe_put(void);
>  
>  u64 __guest_enter(struct kvm_vcpu *vcpu);
>  
> +#ifdef __KVM_NVHE_HYPERVISOR__
> +bool kvm_host_psci_handler(struct kvm_cpu_context *host_ctxt);
> +#endif
> +
>  void __noreturn hyp_panic(void);
>  #ifdef __KVM_NVHE_HYPERVISOR__
>  void __noreturn __hyp_do_panic(bool restore_host, u64 spsr, u64 elr, u64 par);
> diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c
> index cdd7981ea560..7d2270eeecfb 100644
> --- a/arch/arm64/kvm/arm.c
> +++ b/arch/arm64/kvm/arm.c
> @@ -19,6 +19,7 @@
>  #include <linux/kvm_irqfd.h>
>  #include <linux/irqbypass.h>
>  #include <linux/sched/stat.h>
> +#include <linux/psci.h>
>  #include <trace/events/kvm.h>
>  
>  #define CREATE_TRACE_POINTS
> @@ -1514,6 +1515,18 @@ static void init_cpu_logical_map(void)
>  		CHOOSE_NVHE_SYM(__cpu_logical_map)[cpu] = cpu_logical_map(cpu);
>  }
>  
> +static void init_psci_relay(void)
> +{
> +	extern u32 kvm_nvhe_sym(kvm_host_psci_version);
> +	extern u32 kvm_nvhe_sym(kvm_host_psci_function_id)[PSCI_FN_MAX];

nit: I'd rather have these outside of the function body.

> +	int i;
> +
> +	CHOOSE_NVHE_SYM(kvm_host_psci_version) = psci_ops.get_version
> +		? psci_ops.get_version() : PSCI_VERSION(0, 0);

nit: please write this with an if/else construct, it will read a lot
better.

> +	for (i = 0; i < PSCI_FN_MAX; ++i)
> +		CHOOSE_NVHE_SYM(kvm_host_psci_function_id)[i] = psci_get_function_id(i);

Either pick kvm_nvhe_sym(), or CHOOSE_NVHE_SYM(). Having both used
together is just an annoyance (and in this case there is nothing to
choose, really).

> +}
> +
>  static int init_common_resources(void)
>  {
>  	return kvm_set_ipa_limit();
> @@ -1693,6 +1706,7 @@ static int init_hyp_mode(void)
>  	}
>  
>  	init_cpu_logical_map();
> +	init_psci_relay();
>  
>  	return 0;
>  
> diff --git a/arch/arm64/kvm/hyp/nvhe/Makefile b/arch/arm64/kvm/hyp/nvhe/Makefile
> index 2d842e009a40..bf62c8e42ab2 100644
> --- a/arch/arm64/kvm/hyp/nvhe/Makefile
> +++ b/arch/arm64/kvm/hyp/nvhe/Makefile
> @@ -7,7 +7,7 @@ asflags-y := -D__KVM_NVHE_HYPERVISOR__
>  ccflags-y := -D__KVM_NVHE_HYPERVISOR__
>  
>  obj-y := timer-sr.o sysreg-sr.o debug-sr.o switch.o tlb.o hyp-init.o host.o \
> -	 hyp-main.o hyp-smp.o
> +	 hyp-main.o hyp-smp.o psci-relay.o
>  obj-y += ../vgic-v3-sr.o ../aarch32.o ../vgic-v2-cpuif-proxy.o ../entry.o \
>  	 ../fpsimd.o ../hyp-entry.o
>  
> diff --git a/arch/arm64/kvm/hyp/nvhe/hyp-main.c b/arch/arm64/kvm/hyp/nvhe/hyp-main.c
> index 71a17af05953..df4acb40dd39 100644
> --- a/arch/arm64/kvm/hyp/nvhe/hyp-main.c
> +++ b/arch/arm64/kvm/hyp/nvhe/hyp-main.c
> @@ -120,7 +120,11 @@ static void skip_host_instruction(void)
>  
>  static void handle_host_smc(struct kvm_cpu_context *host_ctxt)
>  {
> -	default_host_smc_handler(host_ctxt);
> +	bool handled;
> +
> +	handled = kvm_host_psci_handler(host_ctxt);
> +	if (!handled)
> +		default_host_smc_handler(host_ctxt);
>  
>  	/*
>  	 * Unlike HVC, the return address of an SMC is the instruction's PC.
> diff --git a/arch/arm64/kvm/hyp/nvhe/psci-relay.c b/arch/arm64/kvm/hyp/nvhe/psci-relay.c
> new file mode 100644
> index 000000000000..d75d3f896bfd
> --- /dev/null
> +++ b/arch/arm64/kvm/hyp/nvhe/psci-relay.c
> @@ -0,0 +1,104 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +/*
> + * Copyright (C) 2020 - Google LLC
> + * Author: David Brazdil <[email-masked]>
> + */
> +
> +#include <asm/kvm_asm.h>
> +#include <asm/kvm_hyp.h>
> +#include <asm/kvm_mmu.h>
> +#include <kvm/arm_hypercalls.h>
> +#include <linux/arm-smccc.h>
> +#include <linux/psci.h>
> +#include <kvm/arm_psci.h>
> +#include <uapi/linux/psci.h>
> +
> +/* Config options set by the host. */
> +u32 __ro_after_init kvm_host_psci_version = PSCI_VERSION(0, 0);
> +u32 __ro_after_init kvm_host_psci_function_id[PSCI_FN_MAX];
> +
> +static u64 get_psci_func_id(struct kvm_cpu_context *host_ctxt)
> +{
> +	return host_ctxt->regs.regs[0];
> +}
> +
> +static bool is_psci_0_1_call(u64 func_id)
> +{
> +	unsigned int i;
> +
> +	for (i = 0; i < ARRAY_SIZE(kvm_host_psci_function_id); ++i) {
> +		if (func_id == kvm_host_psci_function_id[i])
> +			return true;
> +	}
> +	return false;
> +}
> +
> +static bool is_psci_0_2_call(u64 func_id)
> +{
> +	/* SMCCC reserves IDs 0x00-1F with the given 32/64-bit base for PSCI. */
> +	return (PSCI_0_2_FN(0) <= func_id && func_id <= PSCI_0_2_FN(31)) ||
> +	       (PSCI_0_2_FN64(0) <= func_id && func_id <= PSCI_0_2_FN64(31));
> +}
> +
> +static bool is_psci_call(u64 func_id)
> +{
> +	switch (kvm_host_psci_version) {
> +	case PSCI_VERSION(0, 0):
> +		return false;
> +	case PSCI_VERSION(0, 1):
> +		return is_psci_0_1_call(func_id);
> +	default:
> +		return is_psci_0_2_call(func_id);
> +	}
> +}
> +
> +static unsigned long psci_0_1_handler(u64 func_id, struct kvm_cpu_context *host_ctxt)
> +{
> +	return PSCI_RET_NOT_SUPPORTED;
> +}
> +
> +static unsigned long psci_0_2_handler(u64 func_id, struct kvm_cpu_context *host_ctxt)
> +{
> +	switch (func_id) {
> +	default:
> +		return PSCI_RET_NOT_SUPPORTED;
> +	}
> +}
> +
> +static unsigned long psci_1_0_handler(u64 func_id, struct kvm_cpu_context *host_ctxt)
> +{
> +	switch (func_id) {
> +	default:
> +		return psci_0_2_handler(func_id, host_ctxt);
> +	}
> +}
> +
> +bool kvm_host_psci_handler(struct kvm_cpu_context *host_ctxt)
> +{
> +	u64 func_id = get_psci_func_id(host_ctxt);
> +	unsigned long ret;
> +
> +	if (!is_psci_call(func_id))
> +		return false;
> +
> +	switch (kvm_host_psci_version) {
> +	case PSCI_VERSION(0, 0):
> +		ret = PSCI_RET_NOT_SUPPORTED;

But isn't that way too late? No PSCI means that we cannot control the
way CPUs boot at all. I think we should completely fail the whole
Protected KVM business if we don't have PSCI.

> +		break;
> +	case PSCI_VERSION(0, 1):
> +		ret = psci_0_1_handler(func_id, host_ctxt);
> +		break;
> +	case PSCI_VERSION(0, 2):
> +		ret = psci_0_2_handler(func_id, host_ctxt);
> +		break;
> +	default:
> +		ret = psci_1_0_handler(func_id, host_ctxt);
> +		break;
> +	}
> +
> +	host_ctxt->regs.regs[0] = ret;
> +	host_ctxt->regs.regs[1] = 0;
> +	host_ctxt->regs.regs[2] = 0;
> +	host_ctxt->regs.regs[3] = 0;
> +	return true;
> +}
> -- 
> 2.29.2.299.gdc1121823c-goog
> 
> 

Thanks,

	M.

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

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