Re: [RFC 1/4] arm64: kvm: add a cpu tear-down function

[Marc Zyngier]

Hi Takahiro,

On 23/03/15 11:53, AKASHI Takahiro wrote:
> Cpu must be put back into its initial state, at least, in the
> following cases in order to shutdown the system and/or re-initialize cpus
> later on:
> 1) kexec/kdump
> 2) cpu hotplug (offline)
> 3) removing kvm as a module
> 
> To address those issues in later patches, this patch adds a tear-down
> function, kvm_cpu_reset(), that disables D-cache & MMU and restore a vector
> table to the initial stub at EL2.

Thanks for having a look at this.

> Signed-off-by: AKASHI Takahiro <takahiro.akashi@xxxxxxxxxx>
> ---
>  arch/arm/kvm/arm.c                |   18 ++++++++++++++++
>  arch/arm/kvm/mmu.c                |   16 +++++++++++++++
>  arch/arm64/include/asm/kvm_asm.h  |    3 +++
>  arch/arm64/include/asm/kvm_host.h |   10 +++++++++
>  arch/arm64/include/asm/kvm_mmu.h  |    3 +++
>  arch/arm64/include/asm/virt.h     |   11 ++++++++++
>  arch/arm64/kvm/hyp-init.S         |   41 +++++++++++++++++++++++++++++++++++++
>  arch/arm64/kvm/hyp.S              |   29 ++++++++++++++++++++++----
>  8 files changed, 127 insertions(+), 4 deletions(-)
> 
> diff --git a/arch/arm/kvm/arm.c b/arch/arm/kvm/arm.c
> index 5560f74..35c8bc0 100644
> --- a/arch/arm/kvm/arm.c
> +++ b/arch/arm/kvm/arm.c
> @@ -897,6 +897,24 @@ static void cpu_init_hyp_mode(void *dummy)
>  	__cpu_init_hyp_mode(boot_pgd_ptr, pgd_ptr, hyp_stack_ptr, vector_ptr);
>  }
>  
> +void kvm_cpu_reset(void *dummy)

Given that the notifier introduced in patch #2 lives in the same file,
this could be made static, couldn't it?

> +{
> +	phys_addr_t boot_pgd_ptr;
> +	phys_addr_t phys_idmap_start;
> +	unsigned long reset_func;
> +	unsigned long vector_ptr;
> +
> +	if (__hyp_get_vectors() == hyp_default_vectors)
> +		return;
> +
> +	reset_func = kvm_reset_func_entry();
> +	boot_pgd_ptr = kvm_mmu_get_boot_httbr();
> +	phys_idmap_start = kvm_get_idmap_start();
> +	vector_ptr = kvm_get_stub_vectors();

Isn't that hyp_default_vectors already?

> +	__cpu_reset_hyp_mode(reset_func,
> +			     boot_pgd_ptr, phys_idmap_start, vector_ptr);
> +}
> +
>  static int hyp_init_cpu_notify(struct notifier_block *self,
>  			       unsigned long action, void *cpu)
>  {
> diff --git a/arch/arm/kvm/mmu.c b/arch/arm/kvm/mmu.c
> index 3e6859b..428f41c 100644
> --- a/arch/arm/kvm/mmu.c
> +++ b/arch/arm/kvm/mmu.c
> @@ -1490,6 +1490,22 @@ phys_addr_t kvm_get_idmap_vector(void)
>  	return hyp_idmap_vector;
>  }
>  
> +phys_addr_t kvm_get_idmap_start(void)
> +{
> +	return hyp_idmap_start;
> +}
> +
> +phys_addr_t kvm_get_stub_vectors(void)
> +{
> +	return virt_to_phys(__hyp_stub_vectors);
> +}

As Geoff already mentioned, this doesn't belong in KVM. But I don't
think you need it, as explained above.

> +
> +unsigned long kvm_reset_func_entry(void)
> +{
> +	/* VA of __kvm_hyp_reset in trampline code */
> +	return TRAMPOLINE_VA + (__kvm_hyp_reset - __hyp_idmap_text_start);
> +}

If you need to compute addresses in the trampoline page, it would be
better to have a generic macro that takes a kernel VA, and turns it into
a trampoline VA.

> +
>  int kvm_mmu_init(void)
>  {
>  	int err;
> diff --git a/arch/arm64/include/asm/kvm_asm.h b/arch/arm64/include/asm/kvm_asm.h
> index 4f7310f..97ee2fc 100644
> --- a/arch/arm64/include/asm/kvm_asm.h
> +++ b/arch/arm64/include/asm/kvm_asm.h
> @@ -116,8 +116,11 @@
>  struct kvm;
>  struct kvm_vcpu;
>  
> +extern char __hyp_stub_vectors[];

Not a KVM thing (for the same reason).

> +
>  extern char __kvm_hyp_init[];
>  extern char __kvm_hyp_init_end[];
> +extern char __kvm_hyp_reset[];
>  
>  extern char __kvm_hyp_vector[];
>  
> diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
> index 8ac3c70..97f88fe 100644
> --- a/arch/arm64/include/asm/kvm_host.h
> +++ b/arch/arm64/include/asm/kvm_host.h
> @@ -199,6 +199,7 @@ struct kvm_vcpu *kvm_arm_get_running_vcpu(void);
>  struct kvm_vcpu * __percpu *kvm_get_running_vcpus(void);
>  
>  u64 kvm_call_hyp(void *hypfn, ...);
> +void kvm_call_reset(unsigned long reset_func, ...);

You seem to have a single call signature for this function, and have
defined all the parameters below. You can drop the variadic aspect.

>  void force_vm_exit(const cpumask_t *mask);
>  void kvm_mmu_wp_memory_region(struct kvm *kvm, int slot);
>  
> @@ -223,6 +224,15 @@ static inline void __cpu_init_hyp_mode(phys_addr_t boot_pgd_ptr,
>  		     hyp_stack_ptr, vector_ptr);
>  }
>  
> +static inline void __cpu_reset_hyp_mode(unsigned long reset_func,
> +					phys_addr_t boot_pgd_ptr,
> +					phys_addr_t phys_idmap_start,
> +					unsigned long stub_vector_ptr)
> +{
> +	kvm_call_reset(reset_func, boot_pgd_ptr,
> +		       phys_idmap_start, stub_vector_ptr);
> +}
> +
>  struct vgic_sr_vectors {
>  	void	*save_vgic;
>  	void	*restore_vgic;
> diff --git a/arch/arm64/include/asm/kvm_mmu.h b/arch/arm64/include/asm/kvm_mmu.h
> index 6458b53..36be582 100644
> --- a/arch/arm64/include/asm/kvm_mmu.h
> +++ b/arch/arm64/include/asm/kvm_mmu.h
> @@ -96,6 +96,9 @@ void kvm_mmu_free_memory_caches(struct kvm_vcpu *vcpu);
>  phys_addr_t kvm_mmu_get_httbr(void);
>  phys_addr_t kvm_mmu_get_boot_httbr(void);
>  phys_addr_t kvm_get_idmap_vector(void);
> +phys_addr_t kvm_get_idmap_start(void);
> +phys_addr_t kvm_get_stub_vectors(void);
> +unsigned long kvm_reset_func_entry(void);
>  int kvm_mmu_init(void);
>  void kvm_clear_hyp_idmap(void);
>  
> diff --git a/arch/arm64/include/asm/virt.h b/arch/arm64/include/asm/virt.h
> index 3070096..7fcd087 100644
> --- a/arch/arm64/include/asm/virt.h
> +++ b/arch/arm64/include/asm/virt.h
> @@ -61,6 +61,17 @@
>  #define BOOT_CPU_MODE_EL1	(0xe11)
>  #define BOOT_CPU_MODE_EL2	(0xe12)
>  
> +/*
> + * HVC_RESET - Reset cpu in EL2 to initial state.
> + *
> + * @x0: entry address in trampoline code in va
> + * @x1: identical mapping page table in pa
> + * @x2: start address of identical mapping in pa
> + * @x3: initial stub vector in pa
> + */
> +
> +#define HVC_RESET 5
> +
>  #ifndef __ASSEMBLY__
>  
>  /*
> diff --git a/arch/arm64/kvm/hyp-init.S b/arch/arm64/kvm/hyp-init.S
> index c319116..ca7e6bf 100644
> --- a/arch/arm64/kvm/hyp-init.S
> +++ b/arch/arm64/kvm/hyp-init.S
> @@ -115,6 +115,47 @@ target: /* We're now in the trampoline code, switch page tables */
>  	eret
>  ENDPROC(__kvm_hyp_init)
>  
> +	/*
> +	 * x0: HYP boot pgd
> +	 * x1: HYP phys_idmap_start
> +	 * x2: HYP stub vectors
> +	 */
> +ENTRY(__kvm_hyp_reset)
> +	/* We're in trampoline code in VA */
> +	/* Invalidate the old TLBs */
> +	tlbi	alle2
> +	dsb	sy

Invalidating the TLBs before switching TTBR0_EL2 is unlikely to have the
effect you want.

> +	/* Switch back to boot page tables */
> +	msr	ttbr0_el2, x0
> +	isb

This is the place where you want TLBI to occur.

> +	/* Branch into PA space */
> +	adr	x0, 1f
> +	bfi	x1, x0, #0, #PAGE_SHIFT
> +	br	x1
> +
> +	/* We're now in idmap */
> +1:	/* Invalidate the old TLBs again */
> +	tlbi	alle2
> +	dsb	sy

See? This is the only TLBI that actually makes sense. Now, given that
you are actually disabling the MMU, I'm not sure these TBLIs make much
sense.

> +	/* Disable MMU */
> +	mrs	x0, sctlr_el2
> +	and	x1, x0, #SCTLR_EL2_EE
> +	orr	x0, x0, x1		// preserve endianness of EL2
> +	ldr	x1, =SCTLR_EL2_FLAGS
> +	eor	x1, x1, xzr
> +	bic	x0, x0, x1		// Clear SCTL_M and etc
> +	msr	sctlr_el2, x0
> +	isb
> +
> +	/* Switch back to stub vectors */
> +	msr	vbar_el2, x2
> +
> +	eret
> +ENDPROC(__kvm_hyp_reset)
> +
>  	.ltorg
>  
>  	.popsection
> diff --git a/arch/arm64/kvm/hyp.S b/arch/arm64/kvm/hyp.S
> index fd085ec..aee75f9 100644
> --- a/arch/arm64/kvm/hyp.S
> +++ b/arch/arm64/kvm/hyp.S
> @@ -1136,6 +1136,11 @@ ENTRY(kvm_call_hyp)
>  	ret
>  ENDPROC(kvm_call_hyp)
>  
> +ENTRY(kvm_call_reset)
> +	hvc	#HVC_RESET
> +	ret
> +ENDPROC(kvm_call_reset)
> +
>  .macro invalid_vector	label, target
>  	.align	2
>  \label:
> @@ -1179,10 +1184,10 @@ el1_sync:					// Guest trapped into EL2
>  	cmp	x18, #HVC_GET_VECTORS
>  	b.ne	1f
>  	mrs	x0, vbar_el2
> -	b	2f
> -
> -1:	/* Default to HVC_CALL_HYP. */
> +	b	3f
>  
> +1:	cmp	x18, #HVC_CALL_HYP
> +	b.ne	2f
>  	push	lr, xzr
>  
>  	/*
> @@ -1196,7 +1201,23 @@ el1_sync:					// Guest trapped into EL2
>  	blr	lr
>  
>  	pop	lr, xzr
> -2:	eret
> +	b	3f
> +
> +	/*
> +	 * shuffle the parameters and jump into trampline code.
> +	 */
> +2:	cmp	x18, #HVC_RESET
> +	b.ne	3f
> +
> +	mov	x18, x0
> +	mov	x0, x1
> +	mov	x1, x2
> +	mov	x2, x3
> +	mov	x3, x4
> +	br	x18

I'd rather move the shuffling of the registers before the HVC call.

> +	/* not reach here */
> +
> +3:	eret
>  
>  el1_trap:
>  	/*
> 

Thanks,

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