linux-kernel - Re: [PATCH v4 2/9] riscv: smp: fail booting up smp if inconsistent vlen is detected

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Date: Wed, 24 Apr 2024 22:01:15 +0200
From: Alexandre Ghiti <alex@...ti.fr>
To: Andy Chiu <andy.chiu@...ive.com>, Paul Walmsley
 <paul.walmsley@...ive.com>, Palmer Dabbelt <palmer@...belt.com>,
 Albert Ou <aou@...s.berkeley.edu>, Conor Dooley
 <conor.dooley@...rochip.com>, Heiko Stuebner <heiko@...ech.de>,
 Guo Ren <guoren@...nel.org>, Conor Dooley <conor@...nel.org>,
 Rob Herring <robh@...nel.org>,
 Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
 Jonathan Corbet <corbet@....net>, Evan Green <evan@...osinc.com>,
 Clément Léger <cleger@...osinc.com>,
 Shuah Khan <shuah@...nel.org>
Cc: linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org,
 Palmer Dabbelt <palmer@...osinc.com>, Vincent Chen
 <vincent.chen@...ive.com>, Greentime Hu <greentime.hu@...ive.com>,
 devicetree@...r.kernel.org, linux-doc@...r.kernel.org,
 linux-kselftest@...r.kernel.org
Subject: Re: [PATCH v4 2/9] riscv: smp: fail booting up smp if inconsistent
 vlen is detected

Hi Andy,

On 12/04/2024 08:48, Andy Chiu wrote:
> Currently we only support Vector for SMP platforms, that is, all SMP
> cores have the same vlenb. If we happen to detect a mismatching vlen, it
> is better to just fail bootting it up to prevent further race/scheduling
> issues.
>
> Also, move .Lsecondary_park forward and chage `tail smp_callin` into a
> regular call in the early assembly. So a core would be parked right
> after a return from smp_callin. Note that a successful smp_callin
> does not return.
>
> Fixes: 7017858eb2d7 ("riscv: Introduce riscv_v_vsize to record size of Vector context")
> Reported-by: Conor Dooley <conor.dooley@...rochip.com>
> Closes: https://lore.kernel.org/linux-riscv/20240228-vicinity-cornstalk-4b8eb5fe5730@spud/
> Signed-off-by: Andy Chiu <andy.chiu@...ive.com>
> ---
> Changelog v4:
>   - update comment also in the assembly code (Yunhui)
> Changelog v2:
>   - update commit message to explain asm code change (Conor)
> ---
>   arch/riscv/kernel/head.S    | 19 ++++++++++++-------
>   arch/riscv/kernel/smpboot.c | 14 +++++++++-----
>   2 files changed, 21 insertions(+), 12 deletions(-)
>
> diff --git a/arch/riscv/kernel/head.S b/arch/riscv/kernel/head.S
> index 4236a69c35cb..a00f7523cb91 100644
> --- a/arch/riscv/kernel/head.S
> +++ b/arch/riscv/kernel/head.S
> @@ -165,9 +165,20 @@ secondary_start_sbi:
>   #endif
>   	call .Lsetup_trap_vector
>   	scs_load_current
> -	tail smp_callin
> +	call smp_callin
>   #endif /* CONFIG_SMP */
>   
> +.align 2
> +.Lsecondary_park:
> +	/*
> +	 * Park this hart if we:
> +	 *  - have too many harts on CONFIG_RISCV_BOOT_SPINWAIT
> +	 *  - receive an early trap, before setup_trap_vector finished
> +	 *  - fail in smp_callin(), as a successful one wouldn't return
> +	 */
> +	wfi
> +	j .Lsecondary_park
> +
>   .align 2
>   .Lsetup_trap_vector:
>   	/* Set trap vector to exception handler */
> @@ -181,12 +192,6 @@ secondary_start_sbi:
>   	csrw CSR_SCRATCH, zero
>   	ret
>   
> -.align 2
> -.Lsecondary_park:
> -	/* We lack SMP support or have too many harts, so park this hart */
> -	wfi
> -	j .Lsecondary_park
> -
>   SYM_CODE_END(_start)
>   
>   SYM_CODE_START(_start_kernel)
> diff --git a/arch/riscv/kernel/smpboot.c b/arch/riscv/kernel/smpboot.c
> index d41090fc3203..673437ccc13d 100644
> --- a/arch/riscv/kernel/smpboot.c
> +++ b/arch/riscv/kernel/smpboot.c
> @@ -214,6 +214,15 @@ asmlinkage __visible void smp_callin(void)
>   	struct mm_struct *mm = &init_mm;
>   	unsigned int curr_cpuid = smp_processor_id();
>   
> +	if (has_vector()) {
> +		/*
> +		 * Return as early as possible so the hart with a mismatching
> +		 * vlen won't boot.
> +		 */
> +		if (riscv_v_setup_vsize())
> +			return;
> +	}
> +
>   	/* All kernel threads share the same mm context.  */
>   	mmgrab(mm);
>   	current->active_mm = mm;
> @@ -226,11 +235,6 @@ asmlinkage __visible void smp_callin(void)
>   	numa_add_cpu(curr_cpuid);
>   	set_cpu_online(curr_cpuid, 1);
>   
> -	if (has_vector()) {
> -		if (riscv_v_setup_vsize())
> -			elf_hwcap &= ~COMPAT_HWCAP_ISA_V;
> -	}
> -
>   	riscv_user_isa_enable();
>   
>   	/*
>

So this should go into -fixes, would you mind sending a single patch for 
this fix?

Your patch 8 is actually already fixed by Clement's patch 
https://lore.kernel.org/linux-riscv/20240409143839.558784-1-cleger@rivosinc.com/ 
and I already mentioned this one to Palmer.

Thanks,

Alex