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

Mark Rutland
2016-12-13T10:53:54Z

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.