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[PATCH V4 6/6] Add API to query supported rseq cs flags

Prakash Sangappa posted 6 patches 7 months, 1 week ago
There is a newer version of this series
[PATCH V4 6/6] Add API to query supported rseq cs flags
Posted by Prakash Sangappa 7 months, 1 week ago 
For the API, add a new flag to sys_rseq 'flags' argument called
RSEQ_FLAG_QUERY_CS_FLAGS.

When this flag is passed it returns a bit mask of all the supported
rseq cs flags in the user provided rseq struct's 'flags' member.

Suggested-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Signed-off-by: Prakash Sangappa <prakash.sangappa@oracle.com>
---
 include/uapi/linux/rseq.h |  1 +
 kernel/rseq.c             | 17 +++++++++++++++++
 2 files changed, 18 insertions(+)

diff --git a/include/uapi/linux/rseq.h b/include/uapi/linux/rseq.h
index 015534f064af..44baea9dd10a 100644
--- a/include/uapi/linux/rseq.h
+++ b/include/uapi/linux/rseq.h
@@ -20,6 +20,7 @@ enum rseq_cpu_id_state {
 
 enum rseq_flags {
 	RSEQ_FLAG_UNREGISTER = (1 << 0),
+	RSEQ_FLAG_QUERY_CS_FLAGS = (1 << 1),
 };
 
 enum rseq_cs_flags_bit {
diff --git a/kernel/rseq.c b/kernel/rseq.c
index c4bc52f8ba9c..997f7ca722ca 100644
--- a/kernel/rseq.c
+++ b/kernel/rseq.c
@@ -576,6 +576,23 @@ SYSCALL_DEFINE4(rseq, struct rseq __user *, rseq, u32, rseq_len,
 		return 0;
 	}
 
+	/*
+	 * return supported rseq_cs flags
+	 * It is an or of all the rseq_cs_flags;
+	 */
+	if (flags & RSEQ_FLAG_QUERY_CS_FLAGS) {
+		u32 rseq_csflags = RSEQ_CS_FLAG_NO_RESTART_ON_PREEMPT |
+				   RSEQ_CS_FLAG_NO_RESTART_ON_SIGNAL  |
+				   RSEQ_CS_FLAG_NO_RESTART_ON_MIGRATE |
+				   RSEQ_CS_FLAG_DELAY_RESCHED |
+				   RSEQ_CS_FLAG_RESCHEDULED;
+		if (!rseq)
+			return -EINVAL;
+		if (copy_to_user(&rseq->flags, &rseq_csflags, sizeof(u32)))
+			return -EFAULT;
+		return 0;
+	}
+
 	if (unlikely(flags))
 		return -EINVAL;
 
-- 
2.43.5
Re: [PATCH V4 6/6] Add API to query supported rseq cs flags
Posted by Mathieu Desnoyers 6 months, 4 weeks ago 
On 2025-05-13 17:45, Prakash Sangappa wrote:
> For the API, add a new flag to sys_rseq 'flags' argument called
> RSEQ_FLAG_QUERY_CS_FLAGS.
> 
> When this flag is passed it returns a bit mask of all the supported
> rseq cs flags in the user provided rseq struct's 'flags' member.
> 
> Suggested-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
> Signed-off-by: Prakash Sangappa <prakash.sangappa@oracle.com>
> ---
>   include/uapi/linux/rseq.h |  1 +
>   kernel/rseq.c             | 17 +++++++++++++++++
>   2 files changed, 18 insertions(+)
> 
> diff --git a/include/uapi/linux/rseq.h b/include/uapi/linux/rseq.h
> index 015534f064af..44baea9dd10a 100644
> --- a/include/uapi/linux/rseq.h
> +++ b/include/uapi/linux/rseq.h
> @@ -20,6 +20,7 @@ enum rseq_cpu_id_state {
>   
>   enum rseq_flags {
>   	RSEQ_FLAG_UNREGISTER = (1 << 0),
> +	RSEQ_FLAG_QUERY_CS_FLAGS = (1 << 1),
>   };
>   
>   enum rseq_cs_flags_bit {
> diff --git a/kernel/rseq.c b/kernel/rseq.c
> index c4bc52f8ba9c..997f7ca722ca 100644
> --- a/kernel/rseq.c
> +++ b/kernel/rseq.c
> @@ -576,6 +576,23 @@ SYSCALL_DEFINE4(rseq, struct rseq __user *, rseq, u32, rseq_len,
>   		return 0;
>   	}
>   
> +	/*
> +	 * return supported rseq_cs flags
> +	 * It is an or of all the rseq_cs_flags;
> +	 */
> +	if (flags & RSEQ_FLAG_QUERY_CS_FLAGS) {
> +		u32 rseq_csflags = RSEQ_CS_FLAG_NO_RESTART_ON_PREEMPT |
> +				   RSEQ_CS_FLAG_NO_RESTART_ON_SIGNAL  |
> +				   RSEQ_CS_FLAG_NO_RESTART_ON_MIGRATE |

Those 3 flags (above) are already or'd by RSEQ_CS_NO_RESTART_FLAGS,
and they are all deprecated. See rseq_warn_flags().

So I would not return them within the set of supported
rseq flags.

Thanks,

Mathieu



> +				   RSEQ_CS_FLAG_DELAY_RESCHED |
> +				   RSEQ_CS_FLAG_RESCHEDULED;
> +		if (!rseq)
> +			return -EINVAL;
> +		if (copy_to_user(&rseq->flags, &rseq_csflags, sizeof(u32)))
> +			return -EFAULT;
> +		return 0;
> +	}
> +
>   	if (unlikely(flags))
>   		return -EINVAL;
>   


-- 
Mathieu Desnoyers
EfficiOS Inc.
https://www.efficios.com
Re: [PATCH V4 6/6] Add API to query supported rseq cs flags
Posted by Prakash Sangappa 6 months, 4 weeks ago 

> On May 23, 2025, at 12:57 PM, Mathieu Desnoyers <mathieu.desnoyers@efficios.com> wrote:
> 
> On 2025-05-13 17:45, Prakash Sangappa wrote:
>> For the API, add a new flag to sys_rseq 'flags' argument called
>> RSEQ_FLAG_QUERY_CS_FLAGS.
>> When this flag is passed it returns a bit mask of all the supported
>> rseq cs flags in the user provided rseq struct's 'flags' member.
>> Suggested-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
>> Signed-off-by: Prakash Sangappa <prakash.sangappa@oracle.com>
>> ---
>>  include/uapi/linux/rseq.h |  1 +
>>  kernel/rseq.c             | 17 +++++++++++++++++
>>  2 files changed, 18 insertions(+)
>> diff --git a/include/uapi/linux/rseq.h b/include/uapi/linux/rseq.h
>> index 015534f064af..44baea9dd10a 100644
>> --- a/include/uapi/linux/rseq.h
>> +++ b/include/uapi/linux/rseq.h
>> @@ -20,6 +20,7 @@ enum rseq_cpu_id_state {
>>    enum rseq_flags {
>>   RSEQ_FLAG_UNREGISTER = (1 << 0),
>> + RSEQ_FLAG_QUERY_CS_FLAGS = (1 << 1),
>>  };
>>    enum rseq_cs_flags_bit {
>> diff --git a/kernel/rseq.c b/kernel/rseq.c
>> index c4bc52f8ba9c..997f7ca722ca 100644
>> --- a/kernel/rseq.c
>> +++ b/kernel/rseq.c
>> @@ -576,6 +576,23 @@ SYSCALL_DEFINE4(rseq, struct rseq __user *, rseq, u32, rseq_len,
>>   return 0;
>>   }
>>  + /*
>> + * return supported rseq_cs flags
>> + * It is an or of all the rseq_cs_flags;
>> + */
>> + if (flags & RSEQ_FLAG_QUERY_CS_FLAGS) {
>> + u32 rseq_csflags = RSEQ_CS_FLAG_NO_RESTART_ON_PREEMPT |
>> +   RSEQ_CS_FLAG_NO_RESTART_ON_SIGNAL  |
>> +   RSEQ_CS_FLAG_NO_RESTART_ON_MIGRATE |
> 
> Those 3 flags (above) are already or'd by RSEQ_CS_NO_RESTART_FLAGS,
> and they are all deprecated. See rseq_warn_flags().
> 
> So I would not return them within the set of supported
> rseq flags.

WIll remove those from the supported flags.

Thanks 
-Prakash.

> 
> Thanks,
> 
> Mathieu
> 
> 
> 
>> +   RSEQ_CS_FLAG_DELAY_RESCHED |
>> +   RSEQ_CS_FLAG_RESCHEDULED;
>> + if (!rseq)
>> + return -EINVAL;
>> + if (copy_to_user(&rseq->flags, &rseq_csflags, sizeof(u32)))
>> + return -EFAULT;
>> + return 0;
>> + }
>> +
>>   if (unlikely(flags))
>>   return -EINVAL;
>>  
> 
> 
> -- 
> Mathieu Desnoyers
> EfficiOS Inc.
> https://www.efficios.com

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