Subject: Re: [PATCH v3] powerpc/pseries: Handle UE event for memcpy_mcsafe

From: Michael Ellerman <[email-masked]>
Date: Tue, 24 Mar 2020 16:27:24 +1100

Ganesh Goudar <[email-masked]> writes:
> If we hit UE at an instruction with a fixup entry, flag to
> ignore the event and set nip to continue execution at the
> fixup entry.

You don't explain why we would want to do that. Or what the consequences
are if we *don't* do it.

As such it's unclear if this is an important fix or just a nice-to-have.

> For powernv these changes are already made by
> commit 895e3dceeb97 ("powerpc/mce: Handle UE event for memcpy_mcsafe")

We have masses of code that supposedly abstracts the MCE logic. How did
we end up in the situation where we're having to write the same fix
twice for different platforms?

cheers

> Reviewed-by: Mahesh Salgaonkar <[email-masked]>
> Reviewed-by: Santosh S <[email-masked]>
> Signed-off-by: Ganesh Goudar <[email-masked]>
> ---
> V2: Fixes a trivial checkpatch error in commit msg.
> V3: Use proper subject prefix.
> ---
>  arch/powerpc/platforms/pseries/ras.c | 8 ++++++++
>  1 file changed, 8 insertions(+)
>
> diff --git a/arch/powerpc/platforms/pseries/ras.c b/arch/powerpc/platforms/pseries/ras.c
> index 43710b69e09e..58e2483fbb1a 100644
> --- a/arch/powerpc/platforms/pseries/ras.c
> +++ b/arch/powerpc/platforms/pseries/ras.c
> @@ -10,6 +10,7 @@
>  #include <linux/fs.h>
>  #include <linux/reboot.h>
>  #include <linux/irq_work.h>
> +#include <linux/extable.h>
>  
>  #include <asm/machdep.h>
>  #include <asm/rtas.h>
> @@ -505,6 +506,7 @@ static int mce_handle_error(struct pt_regs *regs, struct rtas_error_log *errp)
>  	int initiator = rtas_error_initiator(errp);
>  	int severity = rtas_error_severity(errp);
>  	u8 error_type, err_sub_type;
> +	const struct exception_table_entry *entry;
>  
>  	if (initiator == RTAS_INITIATOR_UNKNOWN)
>  		mce_err.initiator = MCE_INITIATOR_UNKNOWN;
> @@ -558,6 +560,12 @@ static int mce_handle_error(struct pt_regs *regs, struct rtas_error_log *errp)
>  	switch (mce_log->error_type) {
>  	case MC_ERROR_TYPE_UE:
>  		mce_err.error_type = MCE_ERROR_TYPE_UE;
> +		entry = search_kernel_exception_table(regs->nip);
> +		if (entry) {
> +			mce_err.ignore_event = true;
> +			regs->nip = extable_fixup(entry);
> +			disposition = RTAS_DISP_FULLY_RECOVERED;
> +		}
>  		switch (err_sub_type) {
>  		case MC_ERROR_UE_IFETCH:
>  			mce_err.u.ue_error_type = MCE_UE_ERROR_IFETCH;
> -- 
> 2.17.2