Subject: [PATCH v4 12/21] arm64: kernel: Survive corrected RAS errors notified by SError

From: [email-masked] (Will Deacon)
Date: Tue, 31 Oct 2017 13:50:42 +0000

On Thu, Oct 19, 2017 at 03:57:58PM +0100, James Morse wrote:
> Prior to v8.2, SError is an uncontainable fatal exception. The v8.2 RAS
> extensions use SError to notify software about RAS errors, these can be
> contained by the ESB instruction.
> 
> An ACPI system with firmware-first may use SError as its 'SEI'
> notification. Future patches may add code to 'claim' this SError as a
> notification.
> 
> Other systems can distinguish these RAS errors from the SError ESR and
> use the AET bits and additional data from RAS-Error registers to handle
> the error. Future patches may add this kernel-first handling.
> 
> Without support for either of these we will panic(), even if we received
> a corrected error. Add code to decode the severity of RAS errors. We can
> safely ignore contained errors where the CPU can continue to make
> progress. For all other errors we continue to panic().
> 
> Signed-off-by: James Morse <[email-masked]>
> Reviewed-by: Catalin Marinas <[email-masked]>
> 
> ---
> I couldn't come up with a concise way to capture 'can continue to make
> progress', so opted for 'blocking' instead.
> 
>  arch/arm64/include/asm/esr.h   | 10 ++++++++
>  arch/arm64/include/asm/traps.h | 36 ++++++++++++++++++++++++++
>  arch/arm64/kernel/traps.c      | 58 ++++++++++++++++++++++++++++++++++++++----
>  3 files changed, 99 insertions(+), 5 deletions(-)
> 
> diff --git a/arch/arm64/include/asm/esr.h b/arch/arm64/include/asm/esr.h
> index 66ed8b6b9976..8ea52f15bf1c 100644
> --- a/arch/arm64/include/asm/esr.h
> +++ b/arch/arm64/include/asm/esr.h
> @@ -85,6 +85,15 @@
>  #define ESR_ELx_WNR_SHIFT	(6)
>  #define ESR_ELx_WNR		(UL(1) << ESR_ELx_WNR_SHIFT)
>  
> +/* Asynchronous Error Type */
> +#define ESR_ELx_AET		(UL(0x7) << 10)

Can you add a #define for the AET shift in the Srror ISS, please? (we have
other blocks in this file for different abort types). e.g.

/* ISS fields definitions for SError interrupts */
#define ESR_ELx_AER_SHIFT	10

then use it below.

> +#define ESR_ELx_AET_UC		(UL(0) << 10)	/* Uncontainable */
> +#define ESR_ELx_AET_UEU		(UL(1) << 10)	/* Uncorrected Unrecoverable */
> +#define ESR_ELx_AET_UEO		(UL(2) << 10)	/* Uncorrected Restartable */
> +#define ESR_ELx_AET_UER		(UL(3) << 10)	/* Uncorrected Recoverable */
> +#define ESR_ELx_AET_CE		(UL(6) << 10)	/* Corrected */
> +
>  /* Shared ISS field definitions for Data/Instruction aborts */
>  #define ESR_ELx_SET_SHIFT	(11)
>  #define ESR_ELx_SET_MASK	(UL(3) << ESR_ELx_SET_SHIFT)
> @@ -99,6 +108,7 @@
>  #define ESR_ELx_FSC		(0x3F)
>  #define ESR_ELx_FSC_TYPE	(0x3C)
>  #define ESR_ELx_FSC_EXTABT	(0x10)
> +#define ESR_ELx_FSC_SERROR	(0x11)
>  #define ESR_ELx_FSC_ACCESS	(0x08)
>  #define ESR_ELx_FSC_FAULT	(0x04)
>  #define ESR_ELx_FSC_PERM	(0x0C)
> diff --git a/arch/arm64/include/asm/traps.h b/arch/arm64/include/asm/traps.h
> index d131501c6222..8d2a1fff5c6b 100644
> --- a/arch/arm64/include/asm/traps.h
> +++ b/arch/arm64/include/asm/traps.h
> @@ -19,6 +19,7 @@
>  #define __ASM_TRAP_H
>  
>  #include <linux/list.h>
> +#include <asm/esr.h>
>  #include <asm/sections.h>
>  
>  struct pt_regs;
> @@ -58,4 +59,39 @@ static inline int in_entry_text(unsigned long ptr)
>  	return ptr >= (unsigned long)&__entry_text_start &&
>  	       ptr < (unsigned long)&__entry_text_end;
>  }
> +
> +static inline bool arm64_is_ras_serror(u32 esr)
> +{
> +	bool impdef = esr & ESR_ELx_ISV; /* aka IDS */

I think you should add an IDS field along with the AET one I suggested.

> +
> +	if (cpus_have_const_cap(ARM64_HAS_RAS_EXTN))
> +		return !impdef;
> +
> +	return false;
> +}
> +
> +/* Return the AET bits of an SError ESR, or 0/uncontainable/uncategorized */
> +static inline u32 arm64_ras_serror_get_severity(u32 esr)
> +{
> +	u32 aet = esr & ESR_ELx_AET;
> +
> +	if (!arm64_is_ras_serror(esr)) {
> +		/* Not a RAS error, we can't interpret the ESR */
> +		return 0;
> +	}
> +
> +	/*
> +	 * AET is RES0 if 'the value returned in the DFSC field is not
> +	 * [ESR_ELx_FSC_SERROR]'
> +	 */
> +	if ((esr & ESR_ELx_FSC) != ESR_ELx_FSC_SERROR) {
> +		/* No severity information */
> +		return 0;
> +	}

Hmm, this means we can't distinguish impdef or RES0 encodings from
uncontainable errors. Is that desirable?

Also, could we end up in a situation where some CPUs support RAS and some
don't, so arm64_is_ras_serror returns false yet a correctable error is
reported by one the CPUs and we treat it as uncontainable?

> +
> +	return aet;
> +}
> +
> +bool arm64_blocking_ras_serror(struct pt_regs *regs, unsigned int esr);
> +void __noreturn arm64_serror_panic(struct pt_regs *regs, u32 esr);
>  #endif
> diff --git a/arch/arm64/kernel/traps.c b/arch/arm64/kernel/traps.c
> index 773aae69c376..53aeb25158b0 100644
> --- a/arch/arm64/kernel/traps.c
> +++ b/arch/arm64/kernel/traps.c
> @@ -709,17 +709,65 @@ asmlinkage void handle_bad_stack(struct pt_regs *regs)
>  }
>  #endif
>  
> -asmlinkage void do_serror(struct pt_regs *regs, unsigned int esr)
> +void __noreturn arm64_serror_panic(struct pt_regs *regs, u32 esr)
>  {
> -	nmi_enter();
> -
>  	console_verbose();
>  
>  	pr_crit("SError Interrupt on CPU%d, code 0x%08x -- %s\n",
>  		smp_processor_id(), esr, esr_get_class_string(esr));
> -	__show_regs(regs);
> +	if (regs)
> +		__show_regs(regs);
> +
> +	/* KVM may call this this from a preemptible context */
> +	preempt_disable();
> +
> +	/*
> +	 * panic() unmasks interrupts, which unmasks SError. Use nmi_panic()
> +	 * to avoid re-entering panic.
> +	 */
> +	nmi_panic(regs, "Asynchronous SError Interrupt");
> +
> +	cpu_park_loop();
> +	unreachable();
> +}
> +
> +bool arm64_blocking_ras_serror(struct pt_regs *regs, unsigned int esr)
> +{

Since you asked... what about "fatal" instead of "blocking"?

Will