Patchwork [v5,09/18] x86/split_lock: Handle #AC exception for split lock

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Submitter Fenghua Yu
Date March 13, 2019, 12:49 a.m.
Message ID <20190313004955.GA31710@romley-ivt3.sc.intel.com>
Download mbox | patch
Permalink /patch/747827/
State New
Headers show

Comments

Fenghua Yu - March 13, 2019, 12:49 a.m.
On Tue, Mar 12, 2019 at 04:51:22PM -0700, Dave Hansen wrote:
> On 3/12/19 4:00 PM, Fenghua Yu wrote:
> I don't see any feature checking here.  Don't we need to see if this MSR
> is supported?
> 
> Shouldn't the code here on systems that don't support split lock
> disabling be the same as on CONFIG_CPU_SUP_INTEL=n systems?

You are right. Is the following #AC handler code better?
Dave Hansen - March 13, 2019, 4:22 p.m.
On 3/12/19 5:49 PM, Fenghua Yu wrote:
> On Tue, Mar 12, 2019 at 04:51:22PM -0700, Dave Hansen wrote:
>> On 3/12/19 4:00 PM, Fenghua Yu wrote:
>> I don't see any feature checking here.  Don't we need to see if this MSR
>> is supported?
>>
>> Shouldn't the code here on systems that don't support split lock
>> disabling be the same as on CONFIG_CPU_SUP_INTEL=n systems?
> 
> You are right. Is the following #AC handler code better?

Fenghua, I'd really appreciate if you could take a deep breath and slow
down.  The most important thing is getting the right patch out and being
as respectful as possible with reviewer bandwidth.

> @@ -293,7 +294,37 @@ DO_ERROR(X86_TRAP_OLD_MF, SIGFPE,           0, NULL, "coprocessor segment overru
>  DO_ERROR(X86_TRAP_TS,     SIGSEGV,          0, NULL, "invalid TSS",         invalid_TSS)
>  DO_ERROR(X86_TRAP_NP,     SIGBUS,           0, NULL, "segment not present", segment_not_present)
>  DO_ERROR(X86_TRAP_SS,     SIGBUS,           0, NULL, "stack segment",       stack_segment)
> -DO_ERROR(X86_TRAP_AC,     SIGBUS,  BUS_ADRALN, NULL, "alignment check",     alignment_check)
> +dotraplinkage void do_alignment_check(struct pt_regs *regs, long error_code)

Is this really an appropriate place to stick this function?  Without any
whitespace, and even pushing out the "#undef" that was here before?

> +{
> +	unsigned int trapnr = X86_TRAP_AC;
> +	char str[] = "alignment check";
> +	int signr = SIGBUS;
> +
> +	RCU_LOCKDEP_WARN(!rcu_is_watching(), "entry code didn't wake RCU");
> +
> +	if (notify_die(DIE_TRAP, str, regs, error_code, trapnr, signr) !=
> +			NOTIFY_STOP) {

Please unindent this code block.

> +		cond_local_irq_enable(regs);
> +		if (!user_mode(regs)) {

Comments please.

The comment about #AC being impossible in the kernel without the split
lock detection feature belongs here, not below.

> +			if (!this_cpu_has(X86_FEATURE_SPLIT_LOCK_DETECT))
> +				return;

Is this consistent with the code that was here before?  Basically, if we
are in the kernel, get an #AC and end up here, we just return from this
function?  Is that what DO_ERROR() did?

> +			/*
> +			 * Only split lock can generate #AC from kernel. Warn
> +			 * and disable #AC for split lock on current CPU.
> +			 */
> +			msr_clear_bit(MSR_TEST_CTL,
> +				      TEST_CTL_ENABLE_SPLIT_LOCK_DETECT_SHIFT);
> +			WARN_ONCE(1, "A split lock issue is detected.\n");

Is it an issue?  I'd probably say: "split lock operation detected"

> +
> +
> +			return;

Extra whitespace.

> +		}
> +		/* Handle #AC generated from user code. */
> +		do_trap(X86_TRAP_AC, SIGBUS, "alignment check", regs,
> +			error_code, BUS_ADRALN, NULL);
> +	}
> +}
>  #undef IP

Patch

diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c
index d26f9e9c3d83..5296021509c7 100644
--- a/arch/x86/kernel/traps.c
+++ b/arch/x86/kernel/traps.c
@@ -61,6 +61,7 @@ 
 #include <asm/mpx.h>
 #include <asm/vm86.h>
 #include <asm/umip.h>
+#include <asm/cpu.h>
 
 #ifdef CONFIG_X86_64
 #include <asm/x86_init.h>
@@ -293,7 +294,37 @@  DO_ERROR(X86_TRAP_OLD_MF, SIGFPE,           0, NULL, "coprocessor segment overru
 DO_ERROR(X86_TRAP_TS,     SIGSEGV,          0, NULL, "invalid TSS",         invalid_TSS)
 DO_ERROR(X86_TRAP_NP,     SIGBUS,           0, NULL, "segment not present", segment_not_present)
 DO_ERROR(X86_TRAP_SS,     SIGBUS,           0, NULL, "stack segment",       stack_segment)
-DO_ERROR(X86_TRAP_AC,     SIGBUS,  BUS_ADRALN, NULL, "alignment check",     alignment_check)
+dotraplinkage void do_alignment_check(struct pt_regs *regs, long error_code)
+{
+	unsigned int trapnr = X86_TRAP_AC;
+	char str[] = "alignment check";
+	int signr = SIGBUS;
+
+	RCU_LOCKDEP_WARN(!rcu_is_watching(), "entry code didn't wake RCU");
+
+	if (notify_die(DIE_TRAP, str, regs, error_code, trapnr, signr) !=
+			NOTIFY_STOP) {
+		cond_local_irq_enable(regs);
+		if (!user_mode(regs)) {
+			if (!this_cpu_has(X86_FEATURE_SPLIT_LOCK_DETECT))
+				return;
+
+			/*
+			 * Only split lock can generate #AC from kernel. Warn
+			 * and disable #AC for split lock on current CPU.
+			 */
+			msr_clear_bit(MSR_TEST_CTL,
+				      TEST_CTL_ENABLE_SPLIT_LOCK_DETECT_SHIFT);
+			WARN_ONCE(1, "A split lock issue is detected.\n");
+
+
+			return;
+		}
+		/* Handle #AC generated from user code. */
+		do_trap(X86_TRAP_AC, SIGBUS, "alignment check", regs,
+			error_code, BUS_ADRALN, NULL);
+	}
+}
 #undef IP
 
 #ifdef CONFIG_VMAP_STACK