Re: [kvm-unit-tests RFC PATCH 09/19] arm/arm64: Zero secondary CPUs' stack

[Nikos Nikoleris <nikos.nikoleris@arm.com>]

On 09/08/2022 10:15, Alexandru Elisei wrote:
> For the boot CPU, the entire stack is zeroed in the entry code. For the
> secondaries, only struct thread_info, which lives at the bottom of the
> stack, is zeroed in thread_info_init().
>

That's a good point.

> Be consistent and zero the entire stack for the secondaries. This should
> also improve reproducibility of the testsuite, as all the stacks now start
> with the same contents, which is zero. And now that all the stacks are
> zeroed in the entry code, there is no need to explicitely zero struct
> thread_info in thread_info_init().
>

Wouldn't it make more sense to call memset(sp, 0, THREAD_SIZE); from 
thread_stack_alloc() instead and avoid doing this in assembly? Do we 
expect anyone to jump to secondary_entry without calling 
thread_stack_alloc() first?

Thanks,

Nikos

> Signed-off-by: Alexandru Elisei <alexandru.elisei@arm.com>
> ---
>   arm/cstart.S          | 6 ++++++
>   arm/cstart64.S        | 3 +++
>   lib/arm/processor.c   | 1 -
>   lib/arm64/processor.c | 1 -
>   4 files changed, 9 insertions(+), 2 deletions(-)
> 
> diff --git a/arm/cstart.S b/arm/cstart.S
> index 39260e0fa470..39e70f40986a 100644
> --- a/arm/cstart.S
> +++ b/arm/cstart.S
> @@ -151,7 +151,13 @@ secondary_entry:
>   	 */
>   	ldr	r1, =secondary_data
>   	ldr	r0, [r1]
> +	mov	r2, r0
> +	lsr	r2, #THREAD_SHIFT
> +	lsl	r2, #THREAD_SHIFT
> +	add	r3, r2, #THREAD_SIZE
> +	zero_range r2, r3, r4, r5
>   	mov	sp, r0
> +
>   	bl	exceptions_init
>   	bl	enable_vfp
>   
> diff --git a/arm/cstart64.S b/arm/cstart64.S
> index d62360cf3859..54773676d1d5 100644
> --- a/arm/cstart64.S
> +++ b/arm/cstart64.S
> @@ -156,6 +156,9 @@ secondary_entry:
>   	/* set the stack */
>   	adrp	x0, secondary_data
>   	ldr	x0, [x0, :lo12:secondary_data]
> +	and	x1, x0, #THREAD_MASK
> +	add	x2, x1, #THREAD_SIZE
> +	zero_range x1, x2
>   	mov	sp, x0
>   
>   	/* finish init in C code */
> diff --git a/lib/arm/processor.c b/lib/arm/processor.c
> index 9d5759686b73..ceff1c0a1bd2 100644
> --- a/lib/arm/processor.c
> +++ b/lib/arm/processor.c
> @@ -117,7 +117,6 @@ void do_handle_exception(enum vector v, struct pt_regs *regs)
>   
>   void thread_info_init(struct thread_info *ti, unsigned int flags)
>   {
> -	memset(ti, 0, sizeof(struct thread_info));
>   	ti->cpu = mpidr_to_cpu(get_mpidr());
>   	ti->flags = flags;
>   }
> diff --git a/lib/arm64/processor.c b/lib/arm64/processor.c
> index 831207c16587..268b2858f0be 100644
> --- a/lib/arm64/processor.c
> +++ b/lib/arm64/processor.c
> @@ -232,7 +232,6 @@ void install_vector_handler(enum vector v, vector_fn fn)
>   
>   static void __thread_info_init(struct thread_info *ti, unsigned int flags)
>   {
> -	memset(ti, 0, sizeof(struct thread_info));
>   	ti->cpu = mpidr_to_cpu(get_mpidr());
>   	ti->flags = flags;
>   }
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