Re: [PATCH v3] powerpc xmon: use `dcbf` inplace of `dcbi` instruction for 64bit Book3S

From: Christophe Leroy <christophe.leroy@c-s.fr>
To: Balamuruhan S <bala24@linux.ibm.com>, mpe@ellerman.id.au
Cc: ravi.bangoria@linux.ibm.com, jniethe5@gmail.com,
	paulus@samba.org, sandipan@linux.ibm.com,
	naveen.n.rao@linux.vnet.ibm.com, linuxppc-dev@lists.ozlabs.org
Subject: Re: [PATCH v3] powerpc xmon: use `dcbf` inplace of `dcbi` instruction for 64bit Book3S
Date: Mon, 30 Mar 2020 10:13:31 +0200	[thread overview]
Message-ID: <e63f665d-80e0-f4c3-dbb2-849f43381c20@c-s.fr> (raw)
In-Reply-To: <20200330075954.538773-1-bala24@linux.ibm.com>


Le 30/03/2020 à 09:59, Balamuruhan S a écrit :
> Data Cache Block Invalidate (dcbi) instruction implemented back in
> PowerPC architecture version 2.03. But as per Power Processor Users Manual
> it is obsolete and not supported by POWER8/POWER9 core. Attempt to use of
> this illegal instruction results in a hypervisor emulation assistance
> interrupt. So, ifdef it out the option `i` in xmon for 64bit Book3S.
> 
> 0:mon> fi
> cpu 0x0: Vector: 700 (Program Check) at [c000000003be74a0]
>      pc: c000000000102030: cacheflush+0x180/0x1a0
>      lr: c000000000101f3c: cacheflush+0x8c/0x1a0
>      sp: c000000003be7730
>     msr: 8000000000081033
>    current = 0xc0000000035e5c00
>    paca    = 0xc000000001910000   irqmask: 0x03   irq_happened: 0x01
>      pid   = 1025, comm = bash
> Linux version 5.6.0-rc5-g5aa19adac (root@ltc-wspoon6) (gcc version 7.4.0
> (Ubuntu 7.4.0-1ubuntu1~18.04.1)) #1 SMP Tue Mar 10 04:38:41 CDT 2020
> cpu 0x0: Exception 700 (Program Check) in xmon, returning to main loop
> [c000000003be7c50] c00000000084abb0 __handle_sysrq+0xf0/0x2a0
> [c000000003be7d00] c00000000084b3c0 write_sysrq_trigger+0xb0/0xe0
> [c000000003be7d30] c0000000004d1edc proc_reg_write+0x8c/0x130
> [c000000003be7d60] c00000000040dc7c __vfs_write+0x3c/0x70
> [c000000003be7d80] c000000000410e70 vfs_write+0xd0/0x210
> [c000000003be7dd0] c00000000041126c ksys_write+0xdc/0x130
> [c000000003be7e20] c00000000000b9d0 system_call+0x5c/0x68
> --- Exception: c01 (System Call) at 00007fffa345e420
> SP (7ffff0b08ab0) is in userspace
> 
> Signed-off-by: Balamuruhan S <bala24@linux.ibm.com>

Reviewed-by: Christophe Leroy <christophe.leroy@c-s.fr>

> ---
>   arch/powerpc/xmon/xmon.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> ---
> changes in v3:
> -------------
> Fix Christophe's review comments and rebase it on latest mpe's merge
> tree,
> 	* mention the dcbi obsolete statement based on Power processor
> 	  users manual in commit message.
> 	* make #ifdef in a more simple way.
> changes in v2:
> -------------
> Fix review comments from Segher and Michael,
>          * change incorrect architecture version 2.01 to 2.03 in commit
>            message.
>          * ifdef it out the option `i` for PPC_BOOK3S_64 instead to drop
> 	  it and change the commit message accordingly.
> 
> diff --git a/arch/powerpc/xmon/xmon.c b/arch/powerpc/xmon/xmon.c
> index ea303b7e4e29..7b62d5dcc4a1 100644
> --- a/arch/powerpc/xmon/xmon.c
> +++ b/arch/powerpc/xmon/xmon.c
> @@ -1808,7 +1808,7 @@ static void cacheflush(void)
>   		catch_memory_errors = 1;
>   		sync();
>   
> -		if (cmd != 'i') {
> +		if (cmd != 'i' || IS_ENABLED(CONFIG_PPC_BOOK3S_64)) {
>   			for (; nflush > 0; --nflush, adrs += L1_CACHE_BYTES)
>   				cflush((void *) adrs);
>   		} else {
> 
> base-commit: 1ad3b5ebe084246ad593a22707cd91ef6418c31e
>