Re: [v3 PATCH 2/5] powerpc/pseries: Fix endainness while restoring of r3 in MCE handler.

From: Nicholas Piggin <npiggin@gmail.com>
To: Mahesh J Salgaonkar <mahesh@linux.vnet.ibm.com>
Cc: linuxppc-dev <linuxppc-dev@ozlabs.org>,
	stable@vger.kernel.org,
	"Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>,
	Michael Ellerman <mpe@ellerman.id.au>,
	Laurent Dufour <ldufour@linux.vnet.ibm.com>
Subject: Re: [v3 PATCH 2/5] powerpc/pseries: Fix endainness while restoring of r3 in MCE handler.
Date: Fri, 8 Jun 2018 11:33:14 +1000	[thread overview]
Message-ID: <20180608113314.02fca098@roar.ozlabs.ibm.com> (raw)
In-Reply-To: <152839249913.25118.1191250274945665204.stgit@jupiter.in.ibm.com>

On Thu, 07 Jun 2018 22:58:33 +0530
Mahesh J Salgaonkar <mahesh@linux.vnet.ibm.com> wrote:

> From: Mahesh Salgaonkar <mahesh@linux.vnet.ibm.com>
> 
> During Machine Check interrupt on pseries platform, register r3 points
> RTAS extended event log passed by hypervisor. Since hypervisor uses r3
> to pass pointer to rtas log, it stores the original r3 value at the
> start of the memory (first 8 bytes) pointed by r3. Since hypervisor
> stores this info and rtas log is in BE format, linux should make
> sure to restore r3 value in correct endian format.
> 
> Without this patch when MCE handler, after recovery, returns to code that
> that caused the MCE may end up with Data SLB access interrupt for invalid
> address followed by kernel panic or hang.
> 
> [   62.878965] Severe Machine check interrupt [Recovered]
> [   62.878968]   NIP [d00000000ca301b8]: init_module+0x1b8/0x338 [bork_kernel]
> [   62.878969]   Initiator: CPU
> [   62.878970]   Error type: SLB [Multihit]
> [   62.878971]     Effective address: d00000000ca70000
> cpu 0xa: Vector: 380 (Data SLB Access) at [c0000000fc7775b0]
>     pc: c0000000009694c0: vsnprintf+0x80/0x480
>     lr: c0000000009698e0: vscnprintf+0x20/0x60
>     sp: c0000000fc777830
>    msr: 8000000002009033
>    dar: a803a30c000000d0
>   current = 0xc00000000bc9ef00
>   paca    = 0xc00000001eca5c00	 softe: 3	 irq_happened: 0x01
>     pid   = 8860, comm = insmod
> [c0000000fc7778b0] c0000000009698e0 vscnprintf+0x20/0x60
> [c0000000fc7778e0] c00000000016b6c4 vprintk_emit+0xb4/0x4b0
> [c0000000fc777960] c00000000016d40c vprintk_func+0x5c/0xd0
> [c0000000fc777980] c00000000016cbb4 printk+0x38/0x4c
> [c0000000fc7779a0] d00000000ca301c0 init_module+0x1c0/0x338 [bork_kernel]
> [c0000000fc777a40] c00000000000d9c4 do_one_initcall+0x54/0x230
> [c0000000fc777b00] c0000000001b3b74 do_init_module+0x8c/0x248
> [c0000000fc777b90] c0000000001b2478 load_module+0x12b8/0x15b0
> [c0000000fc777d30] c0000000001b29e8 sys_finit_module+0xa8/0x110
> [c0000000fc777e30] c00000000000b204 system_call+0x58/0x6c
> --- Exception: c00 (System Call) at 00007fff8bda0644
> SP (7fffdfbfe980) is in userspace
> 
> This patch fixes this issue.

LGTM

Reviewed-by: Nicholas Piggin <npiggin@gmail.com>

> 
> Fixes: a08a53ea4c97 ("powerpc/le: Enable RTAS events support")
> Cc: stable@vger.kernel.org
> Signed-off-by: Mahesh Salgaonkar <mahesh@linux.vnet.ibm.com>
> ---
>  arch/powerpc/platforms/pseries/ras.c |    2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/powerpc/platforms/pseries/ras.c b/arch/powerpc/platforms/pseries/ras.c
> index 5e1ef9150182..2edc673be137 100644
> --- a/arch/powerpc/platforms/pseries/ras.c
> +++ b/arch/powerpc/platforms/pseries/ras.c
> @@ -360,7 +360,7 @@ static struct rtas_error_log *fwnmi_get_errinfo(struct pt_regs *regs)
>  	}
>  
>  	savep = __va(regs->gpr[3]);
> -	regs->gpr[3] = savep[0];	/* restore original r3 */
> +	regs->gpr[3] = be64_to_cpu(savep[0]);	/* restore original r3 */
>  
>  	/* If it isn't an extended log we can use the per cpu 64bit buffer */
>  	h = (struct rtas_error_log *)&savep[1];
>