[PATCH] ARM: soft-reboot into same mode that we entered the kernel

[mark.rutland@arm.com (Mark Rutland)]

Hi,

On Fri, Dec 09, 2016 at 07:49:37PM +0000, Russell King wrote:
> When we soft-reboot (eg, kexec) from one kernel into the next, we need
> to ensure that we enter the new kernel in the same processor mode as
> when we were entered, so that (eg) the new kernel can install its own
> hypervisor - the old kernel's hypervisor will have been overwritten.
> 
> In order to do this, we need to pass a flag to cpu_reset() so it knows
> what to do, and we need to modify the kernel's own hypervisor stub to
> allow it to handle a soft-reboot.
> 
> As we are always guaranteed to install our own hypervisor if we're
> entered in HYP32 mode, and KVM will have moved itself out of the way
> on kexec/normal reboot, we can assume that our hypervisor is in place
> when we want to kexec, so changing our hypervisor API should not be a
> problem.
> 
> Tested-by: Keerthy <j-keerthy@ti.com>
> Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
> ---
> Mark,
> 
> Any opinions on this?
> 
> Thanks.

The above sounds like the right thing to do, but I'm not familiar enough
with the 32-bit hyp + kvm code to say much about the implementation.

Hopefully Dave, Marc, or Christoffer have thoughts.

Otherwise, I only have a couple of minor comments below.

> 
>  arch/arm/include/asm/proc-fns.h |  4 ++--
>  arch/arm/kernel/hyp-stub.S      | 36 ++++++++++++++++++++++++++++++------
>  arch/arm/kernel/reboot.c        | 12 ++++++++++--
>  arch/arm/mm/proc-v7.S           | 12 ++++++++----
>  4 files changed, 50 insertions(+), 14 deletions(-)
> 
> diff --git a/arch/arm/include/asm/proc-fns.h b/arch/arm/include/asm/proc-fns.h
> index 8877ad5ffe10..f2e1af45bd6f 100644
> --- a/arch/arm/include/asm/proc-fns.h
> +++ b/arch/arm/include/asm/proc-fns.h
> @@ -43,7 +43,7 @@ extern struct processor {
>  	/*
>  	 * Special stuff for a reset
>  	 */
> -	void (*reset)(unsigned long addr) __attribute__((noreturn));
> +	void (*reset)(unsigned long addr, bool hvc) __attribute__((noreturn));
>  	/*
>  	 * Idle the processor
>  	 */
> @@ -88,7 +88,7 @@ extern void cpu_set_pte_ext(pte_t *ptep, pte_t pte);
>  #else
>  extern void cpu_set_pte_ext(pte_t *ptep, pte_t pte, unsigned int ext);
>  #endif
> -extern void cpu_reset(unsigned long addr) __attribute__((noreturn));
> +extern void cpu_reset(unsigned long addr, bool hvc) __attribute__((noreturn));
>  
>  /* These three are private to arch/arm/kernel/suspend.c */
>  extern void cpu_do_suspend(void *);
> diff --git a/arch/arm/kernel/hyp-stub.S b/arch/arm/kernel/hyp-stub.S
> index 15d073ae5da2..cab1ac36939d 100644
> --- a/arch/arm/kernel/hyp-stub.S
> +++ b/arch/arm/kernel/hyp-stub.S
> @@ -22,6 +22,9 @@
>  #include <asm/assembler.h>
>  #include <asm/virt.h>
>  
> +#define HVC_GET_VECTORS -1
> +#define HVC_SOFT_RESTART 1
> +
>  #ifndef ZIMAGE
>  /*
>   * For the kernel proper, we need to find out the CPU boot mode long after
> @@ -202,9 +205,18 @@ ARM_BE8(orr	r7, r7, #(1 << 25))     @ HSCTLR.EE
>  ENDPROC(__hyp_stub_install_secondary)
>  
>  __hyp_stub_do_trap:
> -	cmp	r0, #-1
> -	mrceq	p15, 4, r0, c12, c0, 0	@ get HVBAR
> -	mcrne	p15, 4, r0, c12, c0, 0	@ set HVBAR
> +	cmp	r0, #HVC_GET_VECTORS
> +	bne	1f
> +	mrc	p15, 4, r0, c12, c0, 0	@ get HVBAR
> +	b	__hyp_stub_exit
> +
> +1:	teq	r0, #HVC_SOFT_RESTART
> +	bne	1f
> +	mov	r0, r3
> +	bx	r0
> +
> +1:	mcrne	p15, 4, r0, c12, c0, 0	@ set HVBAR
> +__hyp_stub_exit:
>  	__ERET
>  ENDPROC(__hyp_stub_do_trap)
>  
> @@ -231,14 +243,26 @@ ENDPROC(__hyp_stub_do_trap)
>   * initialisation entry point.
>   */
>  ENTRY(__hyp_get_vectors)
> -	mov	r0, #-1
> +	mov	r0, #HVC_GET_VECTORS
> +	__HVC(0)
> +	ret	lr
>  ENDPROC(__hyp_get_vectors)
> -	@ fall through
> +
>  ENTRY(__hyp_set_vectors)
> +	tst	r0, #31
> +	bne	1f
>  	__HVC(0)
> -	ret	lr
> +1:	ret	lr
>  ENDPROC(__hyp_set_vectors)

Why the new check? This looks unrelated to the rest of the patch.

> +ENTRY(__hyp_soft_restart)
> +	mov	r3, r0
> +	mov	r0, #HVC_SOFT_RESTART
> +	__HVC(0)
> +	mov	r0, r3
> +	ret	lr
> +ENDPROC(__hyp_soft_restart)
> +
>  #ifndef ZIMAGE
>  .align 2
>  .L__boot_cpu_mode_offset:
> diff --git a/arch/arm/kernel/reboot.c b/arch/arm/kernel/reboot.c
> index 3fa867a2aae6..f0e3c7f1ea21 100644
> --- a/arch/arm/kernel/reboot.c
> +++ b/arch/arm/kernel/reboot.c
> @@ -12,10 +12,11 @@
>  
>  #include <asm/cacheflush.h>
>  #include <asm/idmap.h>
> +#include <asm/virt.h>
>  
>  #include "reboot.h"
>  
> -typedef void (*phys_reset_t)(unsigned long);
> +typedef void (*phys_reset_t)(unsigned long, bool);
>  
>  /*
>   * Function pointers to optional machine specific functions
> @@ -36,6 +37,7 @@ static u64 soft_restart_stack[16];
>  static void __soft_restart(void *addr)
>  {
>  	phys_reset_t phys_reset;
> +	bool hvc = false;
>  
>  	/* Take out a flat memory mapping. */
>  	setup_mm_for_reboot();
> @@ -51,7 +53,13 @@ static void __soft_restart(void *addr)
>  
>  	/* Switch to the identity mapping. */
>  	phys_reset = (phys_reset_t)virt_to_idmap(cpu_reset);
> -	phys_reset((unsigned long)addr);
> +
> +#ifdef CONFIG_ARM_VIRT_EXT
> +	/* original stub should be restored by kvm */
> +	hvc = is_hyp_mode_available();
> +#endif

When !CONFIG_ARM_VIRT_EXT, is_hyp_mode_available() is defined so as to
always be false, so we can drop the ifdef here.

> +
> +	phys_reset((unsigned long)addr, hvc);
>  
>  	/* Should never get here. */
>  	BUG();
> diff --git a/arch/arm/mm/proc-v7.S b/arch/arm/mm/proc-v7.S
> index d00d52c9de3e..1846ca4255d0 100644
> --- a/arch/arm/mm/proc-v7.S
> +++ b/arch/arm/mm/proc-v7.S
> @@ -53,11 +53,15 @@ ENDPROC(cpu_v7_proc_fin)
>  	.align	5
>  	.pushsection	.idmap.text, "ax"
>  ENTRY(cpu_v7_reset)
> -	mrc	p15, 0, r1, c1, c0, 0		@ ctrl register
> -	bic	r1, r1, #0x1			@ ...............m
> - THUMB(	bic	r1, r1, #1 << 30 )		@ SCTLR.TE (Thumb exceptions)
> -	mcr	p15, 0, r1, c1, c0, 0		@ disable MMU
> +	mrc	p15, 0, r2, c1, c0, 0		@ ctrl register
> +	bic	r2, r2, #0x1			@ ...............m
> + THUMB(	bic	r2, r2, #1 << 30 )		@ SCTLR.TE (Thumb exceptions)
> +	mcr	p15, 0, r2, c1, c0, 0		@ disable MMU
>  	isb
> +#ifdef CONFIG_ARM_VIRT_EXT
> +	teq	r1, #0
> +	bne	__hyp_soft_restart
> +#endif
>  	bx	r0
>  ENDPROC(cpu_v7_reset)
>  	.popsection
> -- 
> 2.7.4

Thanks,
Mark.