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SubjectRe: [PATCH v3 7/8] arm64: exception: handle asynchronous SError interrupt
Hi,

On Thu, Mar 30, 2017 at 06:31:07PM +0800, Xie XiuQi wrote:
> diff --git a/arch/arm64/include/asm/esr.h b/arch/arm64/include/asm/esr.h
> index f20c64a..22f9c90 100644
> --- a/arch/arm64/include/asm/esr.h
> +++ b/arch/arm64/include/asm/esr.h
> @@ -106,6 +106,20 @@
> #define ESR_ELx_AR (UL(1) << 14)
> #define ESR_ELx_CM (UL(1) << 8)
>
> +#define ESR_Elx_DFSC_SEI (0x11)

We should probably have a definition for the uncategorized DFSC value,
too.

[...]

> index 43512d4..d8a7306 100644
> --- a/arch/arm64/kernel/entry.S
> +++ b/arch/arm64/kernel/entry.S
> @@ -69,7 +69,14 @@
> #define BAD_FIQ 2
> #define BAD_ERROR 3
>
> + .arch_extension ras

Generally, arch_extension is a warning sign that code isn't going to
work with contemporary assemblers, which we likely need to support.

> +
> .macro kernel_entry, el, regsize = 64
> +#ifdef CONFIG_ARM64_ESB
> + .if \el == 0
> + esb

Here, I think that we'll need to macro this such that we can build with
existing toolchains.

e.g. in <asm/assembler.h> we need something like:

#define HINT_IMM_ESB 16

.macro ESB
hint #HINT_IMM_ESB
.endm

> + .endif
> +#endif
> sub sp, sp, #S_FRAME_SIZE
> .if \regsize == 32
> mov w0, w0 // zero upper 32 bits of x0
> @@ -208,6 +215,7 @@ alternative_else_nop_endif
> #endif
>
> .if \el == 0
> + msr daifset, #0xF // Set flags

Elsewhere in head.S we use helpers to fiddle with DAIF bits.

Please be consistent with that. Add an enable_all macro if we need one.

> ldr x23, [sp, #S_SP] // load return stack pointer
> msr sp_el0, x23
> #ifdef CONFIG_ARM64_ERRATUM_845719
> @@ -226,6 +234,15 @@ alternative_else_nop_endif
>
> msr elr_el1, x21 // set up the return data
> msr spsr_el1, x22
> +
> +#ifdef CONFIG_ARM64_ESB
> + .if \el == 0
> + esb // Error Synchronization Barrier
> + mrs x21, disr_el1 // Check for deferred error

We'll need an <asm/sysreg.h> definition for this register. With that, we
can use mrs_s here.

> + tbnz x21, #31, el1_sei
> + .endif
> +#endif
> +
> ldp x0, x1, [sp, #16 * 0]
> ldp x2, x3, [sp, #16 * 1]
> ldp x4, x5, [sp, #16 * 2]
> @@ -318,7 +335,7 @@ ENTRY(vectors)
> ventry el1_sync_invalid // Synchronous EL1t
> ventry el1_irq_invalid // IRQ EL1t
> ventry el1_fiq_invalid // FIQ EL1t
> - ventry el1_error_invalid // Error EL1t
> + ventry el1_error // Error EL1t
>
> ventry el1_sync // Synchronous EL1h
> ventry el1_irq // IRQ EL1h
> @@ -328,7 +345,7 @@ ENTRY(vectors)
> ventry el0_sync // Synchronous 64-bit EL0
> ventry el0_irq // IRQ 64-bit EL0
> ventry el0_fiq_invalid // FIQ 64-bit EL0
> - ventry el0_error_invalid // Error 64-bit EL0
> + ventry el0_error // Error 64-bit EL0
>
> #ifdef CONFIG_COMPAT
> ventry el0_sync_compat // Synchronous 32-bit EL0
> @@ -508,12 +525,31 @@ el1_preempt:
> ret x24
> #endif
>
> + .align 6
> +el1_error:
> + kernel_entry 1
> +el1_sei:
> + /*
> + * asynchronous SError interrupt from kernel
> + */
> + mov x0, sp
> + mrs x1, esr_el1

I don't think this is correct if we branched here from kernel_exit.
Surely we want the DISR_EL1 value, and ESR_EL1 is unrelated?

> + mov x2, #1 // exception level of SEI generated
> + b do_sei

You don't need to figure out the EL here. In do_sei() we can determine
the exception level from the regs (e.g. using user_mode(regs)).

> +ENDPROC(el1_error)
> +
> +
> /*
> * EL0 mode handlers.
> */
> .align 6
> el0_sync:
> kernel_entry 0
> +#ifdef CONFIG_ARM64_ESB
> + mrs x26, disr_el1
> + tbnz x26, #31, el0_sei // check DISR.A
> + msr daifclr, #0x4 // unmask SEI
> +#endif

Why do we duplicate this across the EL0 handlers, rather than making it
common in the el0 kernel_entry code?

> mrs x25, esr_el1 // read the syndrome register
> lsr x24, x25, #ESR_ELx_EC_SHIFT // exception class
> cmp x24, #ESR_ELx_EC_SVC64 // SVC in 64-bit state
> @@ -688,8 +724,38 @@ el0_inv:
> ENDPROC(el0_sync)
>
> .align 6
> +el0_error:
> + kernel_entry 0
> +el0_sei:
> + /*
> + * asynchronous SError interrupt from userspace
> + */
> + ct_user_exit
> + mov x0, sp
> + mrs x1, esr_el1

As with el1_sei, I don't think this is correct if we branched to
el0_sei. As far as I am aware, ESR_EL1 will contain whatever exception
we took, and the value we want is in DISR_EL1.

> + mov x2, #0

This EL parameter can go.

> + bl do_sei
> + b ret_to_user
> +ENDPROC(el0_error)
> +
> + .align 6
> el0_irq:
> kernel_entry 0
> +#ifdef CONFIG_ARM64_ESB
> + mrs x26, disr_el1
> + tbz x26, #31, el0_irq_naked // check DISR.A
> +
> + mov x0, sp
> + mrs x1, esr_el1
> + mov x2, 0
> +
> + /*
> + * The SEI generated at EL0 is not affect this irq context,
> + * so after sei handler, we continue process this irq.
> + */
> + bl do_sei
> + msr daifclr, #0x4 // unmask SEI

This rough pattern is duplicated several times across the EL0 entry
paths. I think it should be made common.

> +#endif
> el0_irq_naked:
> enable_dbg
> #ifdef CONFIG_TRACE_IRQFLAGS
> diff --git a/arch/arm64/kernel/traps.c b/arch/arm64/kernel/traps.c
> index b6d6727..99be6d8 100644
> --- a/arch/arm64/kernel/traps.c
> +++ b/arch/arm64/kernel/traps.c
> @@ -643,6 +643,34 @@ asmlinkage void bad_mode(struct pt_regs *regs, int reason, unsigned int esr)
> handler[reason], smp_processor_id(), esr,
> esr_get_class_string(esr));
>
> + die("Oops - bad mode", regs, 0);
> + local_irq_disable();
> + panic("bad mode");
> +}
> +
> +static const char *sei_context[] = {
> + "userspace", /* EL0 */
> + "kernel", /* EL1 */
> +};

This should go. It's only used in one place, and would be clearer with
the strings inline. More on that below.

> +
> +static const char *sei_severity[] = {

Please name this for what it actually represents:

static const char *esr_aet_str[] = {

> + [0 ... ESR_ELx_AET_MAX] = "Unknown",

For consistency with esr_class_str, please make this:

[0 ... ESR_ELx_AET_MAX] = "UNRECOGNIZED AET",

... which makes it clear that this isn't some AET value which reports an
"Unknown" status.

> + [ESR_ELx_AET_UC] = "Uncontainable",
> + [ESR_ELx_AET_UEU] = "Unrecoverable",
> + [ESR_ELx_AET_UEO] = "Restartable",
> + [ESR_ELx_AET_UER] = "Recoverable",
> + [ESR_ELx_AET_CE] = "Corrected",
> +};
> +
> +DEFINE_PER_CPU(int, sei_in_process);

A previous patch added definition of this.

> +asmlinkage void do_sei(struct pt_regs *regs, unsigned int esr, int el)
> +{
> + int aet = ESR_ELx_AET(esr);

The AET field is only valid when the DFSC is 0b010001, so we need to
check that before we interpret AET.

> + console_verbose();
> +
> + pr_crit("Asynchronous SError interrupt detected on CPU%d, %s, %s\n",
> + smp_processor_id(), sei_context[el], sei_severity[aet]);

We should dump the full ESR_ELx value, regardless of what automated
decoding we do, so that we have a chance of debugging issues in the
field.

It would also be nice to align with how bad_mode reports this today.
Please make this:

pr_crit("SError detected on CPU%d while in %s mode: code: 0x%08x -- %s\n",
smp_processor_id(), user_mode(regs) ? "user" : "kernel",
esr, esr_aet_str[aet]);

... though it might be best to dump the raw SPSR rather than trying to
say user/kernel, so that we can distinguish EL1/EL2 with VHE, etc.

> +
> /*
> * In firmware first mode, we could assume firmware will only generate one
> * of cper records at a time. There is no risk for one cpu to parse ghes table.
> @@ -653,9 +681,31 @@ asmlinkage void bad_mode(struct pt_regs *regs, int reason, unsigned int esr)
> this_cpu_dec(sei_in_process);
> }
>
> - die("Oops - bad mode", regs, 0);
> + if (el == 0 && IS_ENABLED(CONFIG_ARM64_ESB) &&

Please use user_mode(regs), and get rid of the el parameter to this
function entirely.

> + cpus_have_cap(ARM64_HAS_RAS_EXTN)) {
> + siginfo_t info;
> + void __user *pc = (void __user *)instruction_pointer(regs);
> +
> + if (aet >= ESR_ELx_AET_UEO)
> + return;

We need to check the DFSC first, and 0b111 is a reserved value (which
the ARM ARM doesn't define the recoverability of), so I don't think this
is correct.

We should probably test the DSFC, then switch on the AET value, so as to
handle only the cases we are aware of.

> +
> + if (aet == ESR_ELx_AET_UEU) {
> + info.si_signo = SIGILL;
> + info.si_errno = 0;
> + info.si_code = ILL_ILLOPC;
> + info.si_addr = pc;

An unrecoverable error is not necessarily a particular bad instruction,
so I'm not sure this makes sense.

Thanks,
Mark.

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