[PATCH 1/1] x86/split_lock: add the source of exception to warning logs

[PATCH 1/1] x86/split_lock: add the source of exception to warning logs

[Dongli Zhang]

Currently to trigger split lock exception at the guest side will print the
below to host logs.

"x86/split lock detection: #AC: CPU 1/KVM/65886 took a split_lock trap at
address: 0x401173"

Although it is more likely the split lock exception is from the guest side,
differentiate if it is from the guest side, or the host userspace
VMM (e.g., QEMU).

Signed-off-by: Dongli Zhang <dongli.zhang@oracle.com>
---
 arch/x86/kernel/cpu/intel.c | 13 +++++++------
 1 file changed, 7 insertions(+), 6 deletions(-)

diff --git a/arch/x86/kernel/cpu/intel.c b/arch/x86/kernel/cpu/intel.c
index a927a8fc9624..22285e7cc138 100644
--- a/arch/x86/kernel/cpu/intel.c
+++ b/arch/x86/kernel/cpu/intel.c
@@ -1155,14 +1155,15 @@ static int splitlock_cpu_offline(unsigned int cpu)
 	return 0;
 }
 
-static void split_lock_warn(unsigned long ip)
+static void split_lock_warn(unsigned long ip, bool is_guest)
 {
 	struct delayed_work *work;
 	int cpu;
 
 	if (!current->reported_split_lock)
-		pr_warn_ratelimited("#AC: %s/%d took a split_lock trap at address: 0x%lx\n",
-				    current->comm, current->pid, ip);
+		pr_warn_ratelimited("#AC: %s/%d (%s) took a split_lock trap at address: 0x%lx\n",
+				    current->comm, current->pid,
+				    is_guest ? "guest" : "user", ip);
 	current->reported_split_lock = 1;
 
 	if (sysctl_sld_mitigate) {
@@ -1194,11 +1195,11 @@ static void split_lock_warn(unsigned long ip)
 bool handle_guest_split_lock(unsigned long ip)
 {
 	if (sld_state == sld_warn) {
-		split_lock_warn(ip);
+		split_lock_warn(ip, true);
 		return true;
 	}
 
-	pr_warn_once("#AC: %s/%d %s split_lock trap at address: 0x%lx\n",
+	pr_warn_once("#AC: %s/%d %s (guest) split_lock trap at address: 0x%lx\n",
 		     current->comm, current->pid,
 		     sld_state == sld_fatal ? "fatal" : "bogus", ip);
 
@@ -1237,7 +1238,7 @@ bool handle_user_split_lock(struct pt_regs *regs, long error_code)
 {
 	if ((regs->flags & X86_EFLAGS_AC) || sld_state == sld_fatal)
 		return false;
-	split_lock_warn(regs->ip);
+	split_lock_warn(regs->ip, false);
 	return true;
 }
 
-- 
2.34.1

Re: [PATCH 1/1] x86/split_lock: add the source of exception to warning logs

[Dave Hansen]

On 2/23/24 01:47, Dongli Zhang wrote:
> @@ -1194,11 +1195,11 @@ static void split_lock_warn(unsigned long ip)
>  bool handle_guest_split_lock(unsigned long ip)
>  {
>  	if (sld_state == sld_warn) {
> -		split_lock_warn(ip);
> +		split_lock_warn(ip, true);
>  		return true;
>  	}

I really despise random true/falses getting passed to functions.

Wouldn't this be a lot easier to read if you just passed the string in:

	split_lock_warn(ip, "guest");

rather than bools plus the ternary form dance?

Re: [PATCH 1/1] x86/split_lock: add the source of exception to warning logs

[Dongli Zhang]

Hi Dave,

On 2/23/24 08:27, Dave Hansen wrote:
> On 2/23/24 01:47, Dongli Zhang wrote:
>> @@ -1194,11 +1195,11 @@ static void split_lock_warn(unsigned long ip)
>>  bool handle_guest_split_lock(unsigned long ip)
>>  {
>>  	if (sld_state == sld_warn) {
>> -		split_lock_warn(ip);
>> +		split_lock_warn(ip, true);
>>  		return true;
>>  	}
> 
> I really despise random true/falses getting passed to functions.
> 
> Wouldn't this be a lot easier to read if you just passed the string in:
> 
> 	split_lock_warn(ip, "guest");
> 
> rather than bools plus the ternary form dance?

Thank you very much!

I will send v2 after waiting if there is no further comment.

Dongli Zhang