linux-kernel - Re: [PATCH] riscv: Move user-visible sbi ext ids to uapi

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Message-Id: <1be32bd0-a3d1-4fea-8f22-e050f664907b@lanxincomputing.com>
Date: Wed, 24 Sep 2025 10:35:25 +0800
From: "BillXiang" <xiangwencheng@...xincomputing.com>
To: "Andrew Jones" <ajones@...tanamicro.com>
Cc: <anup@...infault.org>, <kvm-riscv@...ts.infradead.org>, 
	<linux-kernel@...r.kernel.org>, <paul.walmsley@...ive.com>, 
	<palmer@...belt.com>, <aou@...s.berkeley.edu>, <alex@...ti.fr>, 
	<atishp@...osinc.com>
Subject: Re: [PATCH] riscv: Move user-visible sbi ext ids to uapi

On 9/24/2025 4:14 AM, Andrew Jones wrote:
> On Wed, Sep 17, 2025 at 04:52:46PM +0800, BillXiang wrote:
>> Move those sbi ext ids to uapi because they will be forwarded
>> to user space by kvm.
> 
> We don't need to publish the IDs in UAPI since they are already known to
> userspace by reading the SBI spec. Indeed QEMU already defines all of
> these except for the experimental range.>
> What problem are you trying to solve?


I'm working on rust-vmm[1], which auto-generates the ID constants
from uapi/kvm.h via bindgen[2]. Any ID that isn't exported there is
invisible to us. I expect other VMMs besides QEMU will need these
numbers as well, so let's keep one canonical definition in the UAPI
headers for everyone to share.


[1] https://github.com/rust-vmm
[2] https://crates.io/crates/bindgen

> 
> Thanks,
> drew
> 
>>
>> Signed-off-by: BillXiang <xiangwencheng@...xincomputing.com>
>> ---
>>   arch/riscv/include/asm/sbi.h      | 16 +-----------
>>   arch/riscv/include/uapi/asm/sbi.h | 43 +++++++++++++++++++++++++++++++
>>   2 files changed, 44 insertions(+), 15 deletions(-)
>>   create mode 100644 arch/riscv/include/uapi/asm/sbi.h
>>
>> diff --git a/arch/riscv/include/asm/sbi.h b/arch/riscv/include/asm/sbi.h
>> index 341e74238aa0..e196feaabb2e 100644
>> --- a/arch/riscv/include/asm/sbi.h
>> +++ b/arch/riscv/include/asm/sbi.h
>> @@ -10,13 +10,12 @@
>>   #include <linux/types.h>
>>   #include <linux/cpumask.h>
>>   #include <linux/jump_label.h>
>> +#include <uapi/asm/sbi.h>
>>   
>>   #ifdef CONFIG_RISCV_SBI
>>   enum sbi_ext_id {
>>   #ifdef CONFIG_RISCV_SBI_V01
>>   	SBI_EXT_0_1_SET_TIMER = 0x0,
>> -	SBI_EXT_0_1_CONSOLE_PUTCHAR = 0x1,
>> -	SBI_EXT_0_1_CONSOLE_GETCHAR = 0x2,
>>   	SBI_EXT_0_1_CLEAR_IPI = 0x3,
>>   	SBI_EXT_0_1_SEND_IPI = 0x4,
>>   	SBI_EXT_0_1_REMOTE_FENCE_I = 0x5,
>> @@ -37,13 +36,6 @@ enum sbi_ext_id {
>>   	SBI_EXT_NACL = 0x4E41434C,
>>   	SBI_EXT_FWFT = 0x46574654,
>>   
>> -	/* Experimentals extensions must lie within this range */
>> -	SBI_EXT_EXPERIMENTAL_START = 0x08000000,
>> -	SBI_EXT_EXPERIMENTAL_END = 0x08FFFFFF,
>> -
>> -	/* Vendor extensions must lie within this range */
>> -	SBI_EXT_VENDOR_START = 0x09000000,
>> -	SBI_EXT_VENDOR_END = 0x09FFFFFF,
>>   };
>>   
>>   enum sbi_ext_base_fid {
>> @@ -263,12 +255,6 @@ enum sbi_pmu_ctr_type {
>>   #define SBI_PMU_STOP_FLAG_RESET BIT(0)
>>   #define SBI_PMU_STOP_FLAG_TAKE_SNAPSHOT BIT(1)
>>   
>> -enum sbi_ext_dbcn_fid {
>> -	SBI_EXT_DBCN_CONSOLE_WRITE = 0,
>> -	SBI_EXT_DBCN_CONSOLE_READ = 1,
>> -	SBI_EXT_DBCN_CONSOLE_WRITE_BYTE = 2,
>> -};
>> -
>>   /* SBI STA (steal-time accounting) extension */
>>   enum sbi_ext_sta_fid {
>>   	SBI_EXT_STA_STEAL_TIME_SET_SHMEM = 0,
>> diff --git a/arch/riscv/include/uapi/asm/sbi.h b/arch/riscv/include/uapi/asm/sbi.h
>> new file mode 100644
>> index 000000000000..d29ac0abeefe
>> --- /dev/null
>> +++ b/arch/riscv/include/uapi/asm/sbi.h
>> @@ -0,0 +1,43 @@
>> +/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */
>> +/*
>> + * Copyright (C) 2025 Lanxincomputing Corporation or its affiliates.
>> + *
>> + * Authors:
>> + *     BillXiang <xiangwencheng@...xincomputing.com>
>> + */
>> +
>> +#ifndef _UAPI_ASM_RISCV_SBI_H
>> +#define _UAPI_ASM_RISCV_SBI_H
>> +
>> +
>> +enum SBI_EXT_ID {
>> +	/*
>> +	* The CONSOLE_GETCHAR/CONSOLE_PUTCHAR SBI calls cannot be
>> +	* handled in kernel so they will be forwarded to userspace by kvm.
>> +	*/
>> +	SBI_EXT_0_1_CONSOLE_PUTCHAR = 0x1,
>> +	SBI_EXT_0_1_CONSOLE_GETCHAR = 0x2,
>> +	/*
>> +	* Both SBI experimental and vendor extensions are
>> +	* unconditionally forwarded to userspace by kvm.
>> +	*/
>> +	/* Experimentals extensions must lie within this range */
>> +	SBI_EXT_EXPERIMENTAL_START = 0x08000000,
>> +	SBI_EXT_EXPERIMENTAL_END = 0x08FFFFFF,
>> +
>> +	/* Vendor extensions must lie within this range */
>> +	SBI_EXT_VENDOR_START = 0x09000000,
>> +	SBI_EXT_VENDOR_END = 0x09FFFFFF,
>> +};
>> +
>> +/*
>> +* The SBI debug console functions are unconditionally
>> +* forwarded to the userspace by kvm.
>> +*/
>> +enum sbi_ext_dbcn_fid {
>> +	SBI_EXT_DBCN_CONSOLE_WRITE = 0,
>> +	SBI_EXT_DBCN_CONSOLE_READ = 1,
>> +	SBI_EXT_DBCN_CONSOLE_WRITE_BYTE = 2,
>> +};
>> +
>> +#endif /* _UAPI_ASM_RISCV_SBI_H */
>> \ No newline at end of file
>> -- 
>> 2.43.0